Structural Stability

We demonstrate how by taking better account of electron correlations in the 3d shell of metal ions in nickel oxide it is possible to improve the description of both electron energy loss spectra and parameters characterizing the structural stability of the material compared with local spin density functional theory.

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Structural Stability and Morphogenesis: An Outline of a Genera! Theory of Models Originally published in 1972 IB Stability structureUe et mor phog£n£se Essai d'une tbJorie g6n6rale des modfeles by WA Benjamin, toe. Ubiaiy of Congress ...

The EMD algorithm is a technique that aims to decompose into their building blocks functions that are the superposition of a (reasonably) small number of components, well separated in the time-frequency plane, each of which can be viewed as approximately harmonic locally, with slowly varying amplitudes and frequencies. The EMD has already shown its usefulness in a wide range of applications including meteorology, structural stability analysis, medical studies. On the other hand, the EMD algorithm contains heuristic and ad hoc elements that make it hard to analyze mathematically. In this paper we describe a method that captures the flavor and philosophy of the EMD approach, albeit using a different approach in constructing the components. The proposed method is a combination of wavelet analysis and reallocation method. We introduce a precise mathematical definition for a class of functions that can be viewed as a superposition of a reasonably small number of approximately harmonic components, and we prove that our method does indeed succeed in decomposing arbitrary functions in this class. We provide several examples, for simulated as well as real data.

Practical components for three-dimensional molecular nanofabrication must be simple to produce, stereopure, rigid, and adaptable. We report a family of DNA tetrahedra, less than 10 nanometers on a side, that can self-assemble in seconds with near-quantitative yield of one diastereomer. They can be connected by programmable DNA linkers. Their triangulated architecture confers structural stability; by compressing a DNA tetrahedron with an atomic force microscope, we have measured the axial compressibility of DNA and observed the buckling of the double helix under high loads.

Vinyl-functionalized MCM-41 samples were prepared by either a postsynthesis grafting (PSG) process or a direct co-condensation synthesis. The structures, stabilities, and reactivities of products from both methods were compared. The mesoscopic order of the hexagonal pore structure of vinyl-grafted MCM-41 (v-gr-MCM-41) resembled that of the MCM-41 host. On the basis of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and bromination kinetics data, the vinyl groups appeared to be nonuniformly distributed in v-gr-MCM-41 prepared by the present PSG process, with a large proportion of vinyl groups on the external surface of the crystallites or inside channels but near the channel openings. The mesoscopic order of products from the direct synthesis (v-MCM-41) depended on the type of alkoxysilane precursor used and on the ratio of vinylsiloxane to alkoxysilane in the reaction mixture. The vinyl groups appeared to be more uniformly distributed in v-MCM-41. Vinyl-grafted MCM-41 exhibited greater hydrothermal stability than unmodified MCM-41 and was capable of absorbing nonpolar solvents from aqueous mixtures or emulsions.

In this paper we report on the activity of Cu-and Ni-containing cerium oxide catalysts for low-temperature water-gas shift (WGS). Bulk catalysts were prepared in nanocrystalline form by the urea co-precipitation-gelation method. Lanthanum dopant (10 at.%) was used as a structural stabilizer of ceria, while the content of Cu or Ni was in the range of 5-15 at.% (2-8 wt.%). At low metal loadings, Cu or Ni were present in the form of highly dispersed oxide clusters, while at high loadings, clusters as well as particles of CuO or NiO (>10 nm in size) were present on ceria. Both Cu and Ni increased the reducibility of ceria, as evidenced by H 2 -TPR experiments. The WGS reaction activity of Ce(La)O x was increased significantly by addition of a small amount (2 wt.%) of Cu or Ni. The catalysts were not activated prior to testing. Steady-state WGS kinetics were measured over the temperature range of 175-300 and 250-300 • C, respectively, for Cu-and Ni-Ce(La)O x . The activation energy of the reaction over Ce(La)O x was 58.5 kJ/mol, while it was 38.2 and 30.4 kJ/mol, respectively, over the 5 at.% Ni-Ce(La)O x and 5 at.% Cu-Ce(La)O x catalysts in CO-rich conditions. A co-operative redox reaction mechanism, involving oxidation of CO adsorbed on the metal cluster by oxygen supplied to the metal interface by ceria, followed by H 2 O capping the oxygen vacancy on ceria, was used to fit the kinetics. Parametric studies were mainly performed with the 5 at.% Cu-(La)O x catalyst. Notably, this material requires no activation and retains high WGS activity and stability at temperatures up to 600 • C. because of its potential use in conjunction with fuel-cell power generation. The fuel-cell technology, an attractive, energy-efficient process, is currently undergoing rapid development for both power plant and transportation applications. In the transportation sector, fuel cells could replace the internal combustion engine in cars, trucks, buses, etc. and meet the most stringent emission regulations.

Techniques from graph theory are applied to analyze the bond networks in proteins and identify the flexible and rigid regions. The bond network consists of distance constraints defined by the covalent and hydrogen bonds and salt bridges in the protein, identified by geometric and energetic criteria. We use an algorithm that counts the degrees of freedom within this constraint network and that identifies all the rigid and flexible substructures in the protein, including overconstrained regions (with more crosslinking bonds than are needed to rigidify the region) and underconstrained or flexible regions, in which dihedral bond rotations can occur. The number of extra constraints or remaining degrees of bond-rotational freedom within a substructure quantifies its relative rigidity/flexibility and provides a flexibility index for each bond in the structure. This novel computational procedure, first used in the analysis of glassy materials, is approximately a million times faster than molecular dynamics simulations and captures the essential conformational flexibility of the protein main and side-chains from analysis of a single, static threedimensional structure. This approach is demonstrated by comparison with experimental measures of flexibility for three proteins in which hinge and loop motion are essential for biological function: HIV protease, adenylate kinase, and dihydrofolate reductase. Proteins 2001;44:150 -165.

Nanometre-scale contact experiments 1-6 and simulations 7-10 demonstrate the potential to probe incipient plasticity-the onset of permanent deformation-in crystals. Such studies also point to the need for an understanding of the mechanisms governing defect nucleation in a broad range of fields and applications. Here we present a fundamental framework for describing incipient plasticity that combines results of atomistic and finite-element modelling, theoretical concepts of structural stability at finite strain, and experimental analysis. We quantify two key features of the nucleation and subsequent evolution of defects. A position-sensitive criterion based on elastic stability determines the location and character of homogeneously nucleated defects. We validate this stability criterion at both the atomistic and the continuum levels. We then propose a detailed interpretation of the experimentally observed sequence of displacement bursts to elucidate the role of secondary defect sources operating locally at stress levels considerably smaller than the ideal strength required for homogeneous nucleation. These findings provide a self-consistent explanation of the discontinuous elastic-plastic response in nanoindentation measurements, and a guide to fundamental studies across many disciplines that seek to quantify and predict the initiation and early stages of plasticity.

Hemicellulose is a complex group of heterogeneous polymers and represents one of the major sources of renewable organic matter. Mannan is one of the major constituent groups of hemicellulose in the wall of higher plants. It comprises linear or branched polymers derived from sugars such as D-mannose, D-galactose, and D-glucose. The principal component of softwood hemicellulose is glucomannan. Structural studies revealed that the galactosyl side chain hydrogen interacts to the mannan backbone intramolecularly and provides structural stability. Differences in the distribution of D-galactosyl units along the mannan structure are found in galactomannans from different sources. Acetyl groups were identified and distributed irregularly in glucomannan. Some of the mannosyl units of galactoglucomannan are partially substituted by O-acetyl groups. Some unusual structures are found in the mannan family from seaweed, showing a complex system of sulfated structure. Endohydrolases and exohydrolases are involved in the breakdown of the mannan backbone to oligosaccharides or fermentable sugars. The main-chain mannan-degrading enzymes include β-mannanase, β-glucosidase, and β-mannosidase. Additional enzymes such as acetyl mannan esterase and αgalactosidase are required to remove side-chain substituents that are attached at various points on mannan, creating more sites for subsequent enzymatic hydrolysis. Mannandegrading enzymes have found applications in the pharmaceutical, food, feed, and pulp and paper industries. This review reports the structure of mannans and some bio-chemical properties and applications of mannan-degrading enzymes.

We study the various linear responses of neutron stars to external relativistic tidal fields. We focus on three different tidal responses, associated to three different tidal coefficients: (i) a gravito-electrictype coefficient Gµ ℓ = [length] 2ℓ+1 measuring the ℓ th -order mass multipolar moment GMa 1 ...a ℓ induced in a star by an external ℓ th -order gravito-electric tidal field Ga 1 ...a ℓ ; (ii) a gravito-magnetictype coefficient Gσ ℓ = [length] 2ℓ+1 measuring the ℓ th spin multipole moment GSa 1 ...a ℓ induced in a star by an external ℓ th -order gravito-magnetic tidal field Ha 1 ...a ℓ ; and (iii) a dimensionless "shape" Love number h ℓ measuring the distortion of the shape of the surface of a star by an external ℓ thorder gravito-electric tidal field. All the dimensionless tidal coefficients Gµ ℓ /R 2ℓ+1 , Gσ ℓ /R 2ℓ+1 and h ℓ (where R is the radius of the star) are found to have a strong sensitivity to the value of the star's "compactness" c ≡ GM/(c 2 0 R) (where we indicate by c0 the speed of light). In particular, Gµ ℓ /R 2ℓ+1 ∼ k ℓ is found to strongly decrease, as c increases, down to a zero value as c is formally extended to the "black-hole limit" (BH) c BH = 1/2. The shape Love number h ℓ is also found to significantly decrease as c increases, though it does not vanish in the formal limit c → c BH , but is rather found to agree with the recently determined shape Love numbers of black holes. The formal vanishing of µ ℓ and σ ℓ as c → c BH is a consequence of the no-hair properties of black holes. This vanishing suggests, but in no way proves, that the effective action describing the gravitational interactions of black holes may not need to be augmented by nonminimal worldline couplings.

The subventricular zone remains mitotically active throughout life in rodents. Studies with tritiated thymidine, which is incorporated into the DNA of mitotic cells, have revealed that the rodent subventricular zone produces neuroblasts that migrate toward the olfactory bulb along the rostral migratory stream. A similar migratory stream has been documented in monkeys by using the thymidine analogue BrdUrd. The same approach showed that neurogenesis occurred in the dentate gyrus of adult primates, including humans. In the present study, experiments combining injections of BrdUrd and the dye 1,1-dioctadecyl-3,3,3,3-tetramethylindo-carbocyanine, with the immunostaining for molecular markers of neurogenesis (polysialylated neural cell adhesion molecule, ␤-tubulin-III, collapsin response mediator protein-4, neuronal nuclear protein) in New World (Saimiri sciureus) and Old World (Macaca fascicularis) monkeys have revealed that new neurons are produced in the amygdala, piriform cortex, and adjoining inferior temporal cortex in adult primates. These newborn neurons expressed the antiapoptotic protein Bcl-2 and formed a more-or-less continuous pathway that extended from the tip of the temporal ventricular horn to the deep portion of the temporal lobe. The production of newborn neurons in the amygdala, piriform cortex, and inferior temporal cortex seems to parallel the continuing addition of neurons in the olfactory bulb. These two concomitant phenomena may ensure structural stability and functional plasticity to the primate olfactory system and temporal lobe. N eurogenesis is known to occur throughout life in specific areas of the mammalian brain, principally the dentate gyrus of the hippocampus and the subventricular zone (SVZ) that lines the lateral ventricles (1, 2). Adult SVZ produces neuroblasts that migrate tangentially toward the olfactory bulb along the socalled rostral migratory stream (RMS) (3, 4). Tangential migration is rare in embryonic brain development, but more than 50% of neurons generated prenatally in rodents seem to migrate tangentially for a certain distance before their final radial implantation (5). Therefore, it can be expected that a majority of neurons produced in mature brain would follow a tangential route to reach implantation level. In any event, the fact that migrating chains have been observed along the entire lateral ventricle system (6, 7) raises the possibility of the existence of migratory streams other than the RMS. Indeed, evidence shows that new neurons are produced in various neocortical regions in monkeys , but these cells seem to be transient .

the wiggler in which the interaction between laser and electron occurs. For a bend magnet located immediately following the wiggler (as shown in ), the stretching of the electron distribution due to time-of-flight effects will be reduced by a factor of 3, resulting in an x-ray pulse duration of ϳ100 fs. In addition, the temporal structure of the electron distribution will give rise to the emission of a single-cycle infrared pulse ( o ϳ 120 m) that is spatially and temporally coherent (12,.

The AXO 4 monazite-type compounds form an extended family that is described in this review in terms of field of stability versus composition. All the substitution possibilities on the cationic and anionic sites leading to the monazite structure are reported. The phosphate, vanadate, chromate, arseniate, sulphate and silicate families are described and the unit-cell parameters of pure compounds and solid solutions are gathered. The stability limits of the monazite-type structure are discussed versus several models generally correlated with geometric criteria. The effects of physicochemical parameters such as pressure, temperature and irradiation on the monazite-type structure stability are also discussed. The structural relationships between the monazite structure and the related structures (zircon, anhydrite, barite, AgMnO 4 , scheelite and monoclinic BiPO 4 , CaSeO 3 , rhabdophane and SrNp(PO 4 ) 2 ) are described.

Variations of extracellular polymeric substances (EPS) and its components with sludge granulation were examined in a lab-scale sequencing batch reactor (SBR) which was fed with sodium nitrate and sodium acetate. Ultrasonication plus cation exchange resin (CER) were used as the EPS extraction method. Results showed that after approximately 90 d cultivation, the sludge in the reactor was almost granulated. The content of extracellular polysaccharides increased from 10.36 mg/g-VSS (volatile suspended solids) at start-up with flocculent sludge to 23.18 mg/g-VSS at 91 d with matured granular sludge, while the content of extracellular proteins were almost unchanged. Polysaccharides were the major components of EPS in anoxic granular sludge, accounting for about 70.6-79.0%, while proteins and DNA accounted for about 16.5-18.9% and 4.6-9.9%, respectively. It is proposed that EPS play a positive role in anoxic sludge granulation and polysaccharides might be strongly involved in aggregation of flocs into granules.

The synthesis of geopolymer matrixes from coal (co-)combustion fly ashes as the sole source of silica and alumina has been studied in order to assess both their capacity to immobilise the potentially toxic elements contained in these coal (co-)combustion by-products and their suitability to be used as cement replacements. The geopolymerisation process has been performed using (5, 8 and 12 M) NaOH solutions as activation media and different curing time (6-48 h) and temperature (40-80 • C) conditions. Synthesised geopolymers have been characterised with regard to their leaching behaviour, following the DIN 38414-S4 [DIN 38414-S4, Determination of leachability by water (S4), group S: sludge and sediments. German standard methods for the examination of water, waste water and sludge. Institut für Normung, Berlin, 1984] and NEN 7375 [NEN 7375, Leaching characteristics of moulded or monolithic building and waste materials. Determination of leaching of inorganic components with the diffusion test. Netherlands Normalisation Institute, Delft, 2004] procedures, and to their structural stability by means of compressive strength measurements. In addition, geopolymer mineralogy, morphology and structure have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. It was found that synthesised geopolymer matrixes were only effective in the chemical immobilisation of a number of elements of environmental concern contained in fly ashes, reducing (especially for Ba), or maintaining their leachable contents after the geopolymerisation process, but not for those elements present as oxyanions. Physical entrapment does not seem either to contribute in an important way, in general, to the immobilisation of oxyanions. The structural stability of synthesised geopolymers was mainly dependent on the glass content of fly ashes, attaining at the optimal activation conditions (12 M NaOH, 48 h, 80 • C) compressive strength values about 60 MPa when the fly ash glass content was higher than 90%.

Reactivation of the p53 cell apoptosis pathway through inhibition of the p53-hDM2 interaction is a viable approach to suppress tumor growth in many human cancers and stabilization of the helical structure of synthetic p53 analogs via a hydrocarbon cross-link (staple) has been found to lead to increased potency and inhibition of proteinprotein binding (J. Am. Chem. Soc. 129: 5298). However, details of the structure and dynamic stability of the stapled peptides are not well understood. Here, we use extensive all-atom molecular dynamics simulations to study a series of stapled a-helical peptides over a range of temperatures in solution. The peptides are found to exhibit substantial variations in predicted a-helical propensities that are in good agreement with the experimental observations. In addition, we find significant variation in local structural flexibility of the peptides with the position of the linker, which appears to be more closely related to the observed differences in activity than the absolute a-helical stability. These simulations provide new insights into the design of a-helical stapled peptides and the development of potent inhibitors of a-helical protein-protein interfaces.

Has the persistence of inflation in the United States changed since 1965? We estimate the persistence of inflation over time using different measures and estimation procedures and we produce confidence intervals for our estimates as well as formal tests of unchanged persistence. We find that inflation persistence has been high and approximately unchanged in the U.S. over our sample period. We reconcile our results with other studies that reached different conclusions. r (R. Reis).

The measurement of amino acid-resolved hydrogen exchange (HX) has provided the most detailed information so far available on the structure and properties of protein folding intermediates. Direct HX measurements can define the structure of tenuous molten globule forms that are generally inaccessible to the usual crystallographic and NMR methods (C. Redfield review in this issue). HX pulse labeling methods can specify the structure, stability and kinetics of folding intermediates that exist for less than 1 s during kinetic folding. Native state HX methods can detect and characterize folding intermediates that exist as infinitesimally populated high energy excited state forms under native conditions. The results obtained in these ways suggest principles that appear to explain the properties of partially folded intermediates and how they are organized into folding pathways. The application of these methods is detailed here.

The contributions of individual components in extracellular polymeric substances (EPSs) on structural stability of phenol-fed, aerobic granules were examined. The roles of proteins, aand b-polysaccharides, and lipids were studied via their selective hydrolysis using enzymes, and the structural changes of granule were probed using in situ fluorescent staining and confocal laser scanning microscopy. Selective enzymatic hydrolysis of proteins, lipids, and a-polysaccharides had a minimal effect upon the three-dimensional structural integrity of the granules. Conversely, selective hydrolysis of b-polysaccharides fragmented the granules. The b-polysaccharides were expected to form the backbone of a network-like outer layer with embedded proteins, lipids, a-polysaccharides, and cells to support the mechanical stability of granules.

Tuberculosis is still a leading cause of death in developing countries, for which there is an urgent need for new pharmacological agents. The synthesis of the novel antimycobacterial drug class of benzothiazinones (BTZs) and the identification of their cellular target as DprE1 (Rv3790), a component of the decaprenylphosphoryl-β-d-ribose 2′-epimerase complex, have been reported recently. Here, we describe the identification and characterization of a novel resistance mechanism to BTZ in Mycobacterium smegmatis. The overexpression of the nitroreductase NfnB leads to the inactivation of the drug by reduction of a critical nitro-group to an amino-group. The direct involvement of NfnB in the inactivation of the lead compound BTZ043 was demonstrated by enzymology, microbiological assays and gene knockout experiments. We also report the crystal structure of NfnB in complex with the essential cofactor flavin mononucleotide, and show that a common amino acid stretch between NfnB and DprE1 is likely to be essential for the interaction with BTZ. We performed docking analysis of NfnB-BTZ in order to understand their interaction and the mechanism of nitroreduction. Although Mycobacterium tuberculosis seems to lack nitroreductases able to inactivate these drugs, our findings are valuable for the design of new BTZ molecules, which may be more effective in vivo.

Structural and electronic properties of CaCu3Ti4O12 have been calculated using density-functional theory within the local spin-density approximation. After an analysis of structural stability, zonecenter optical phonon frequencies are evaluated using the frozen-phonon method, and mode effective charges are determined from computed Berry-phase polarizations. Excellent agreement between calculated and measured phonon frequencies is obtained; calculated mode effective charges are in poorer agreement with experiment, although they are of the correct order of magnitude; and the lattice contribution to the static dielectric constant is calculated to be ∼40. On the basis of these results, various mechanisms are considered for the enormous dielectric response reported in recent experiments. No direct evidence is found for intrinsic lattice or electronic mechanisms, suggesting that increased attention should be given to extrinsic effects.

Relative length is a constant and distinctive characteristic for each autosomal SC, despite variations in absolute length from cell to cell. Arm ratio is distinctive for each SC except for two of the three sub-acrocentrics, and serves, together with relative length, for identification. The constancy of relative length and arm ratios indicates biological stability and lack of physical distortion in these spread preparations. There is a 1∶1 relationship between relative lengths of autosomal SCs and mitotic autosomes; their arm ratios are also similar. These close parallels provide strikingly similar SC and somatic karyotypes. Variability was observed in sub-acrocentric arm ratios and in lengths of unpaired X and Y axes, correlated with the presence of constitutive heterochromatin. — Utilizing progressive differentiations of the X and Y chromosomes for staging, it is demonstrated that autosomal SCs decrease in length from late zygotene to mid-pachytene, and then increase at late pachytene. Within a nucleus, synchrony of length changes is maintained. It is concluded that the factors governing autosomal SC length are regular for any given bivalent from cell to cell, and may be related to those that control somatic autosome length relationships. — The X and Y axes differ quantitatively as well as qualitatively from autosomal SCs. The SC portion of the X and Y is constant in length through most of pachytene; the unpaired axes shorten and lengthen, but not in proportion to autosomal SCs. X and Y relative lengths and arm ratios vary throughout pachytene and do not maintain proportionality with somatic values. The evidence suggests, but does not prove, that the long arm of the X is paired with the short arm of the Y. — Twists occur in autosomal SCs at increasing frequencies throughout pachytene but cannot account for length changes. The number of twists per SC is directly proportional to SC length. Intertwining of SCs is random and proportional to SC length. End-to-end associations of autosomal SCs appear to be random; however, the ends of the X and Y are less often involved in such connections. — The length of axial material in all chromosomes at pachytene, expressed as an equivalent length of DNA double helix, represents 0.013% of the diploid DNA complement.

Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha À1 2 year À1) combined with P, K and N fertiliser application on total organic C (C T), labile C (C L), non-labile C (C NL), total N (N T), mean weight diameter (MWD) and unsaturated hydraulic conductivity (K unsat) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha À1 year À1) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly C L , where application of 30 t ha À1 2 year À1 increased C L by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while N T increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased K unsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha À1 year À1 of FYM increased concentrations of C L by 173% and of C NL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, N T and MWD compared with the cropped site, while K unsat (10 mm tension) was increased on the 0 and 50 t ha À1 year À1 treatments as a result of a recent tillage. There was no difference in K unsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha À1 year À1. There were similar significant positive correlations of all C fractions and N T with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and N T with K unsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and K unsat was with C L. This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the www.elsevier.com/locate/still Soil & Tillage Research 91 (2006) 39-47 DOIs of related articles

We relate the unfolding of a protein to its loss of structural stability or rigidity. Rigidity and flexibility are well defined concepts in mathematics and physics, with a body of theorems and algorithms that have been applied successfully to materials, allowing the constraints in a network to be related to its deformability. Here we simulate the weakening or dilution of the noncovalent bonds during protein unfolding, and identify the emergence of flexible regions as unfolding proceeds. The transition state is determined from the inflection point in the change in the number of independent bond-rotational degrees of freedom (floppy modes) of the protein as its mean atomic coordination decreases. The first derivative of the fraction of floppy modes as a function of mean coordination is similar to the fraction-folded curve for a protein as a function of denaturant concentration or temperature. The second derivative, a specific heat-like quantity, shows a peak around a mean coordination of ͗r͘ ‫؍‬ 2.41 for the 26 diverse proteins we have studied. As the protein denatures, it loses rigidity at the transition state, proceeds to a state where just the initial folding core remains stable, then becomes entirely denatured or flexible. This universal behavior for proteins of diverse architecture, including monomers and oligomers, is analogous to the rigid to floppy phase transition in network glasses. This approach provides a unifying view of the phase transitions of proteins and glasses, and identifies the mean coordination as the relevant structural variable, or reaction coordinate, along the unfolding pathway.

structure and its activity. This paper is an attempt to a better A proteolytic enzyme, a-chymotrypsin, and a lipolytic enzyme, understanding of the properties of a proteolytic enzyme (acutinase, were adsorbed from aqueous solution onto a hydrophobic chymotrypsin) and a lipolytic enzyme (cutinase) when they Teflon surface and a hydrophilic silica surface. We investigated are immobilized on a solid support. the influence of adsorption on the structure, the structure thermal Nowadays, various ways of immobilizing enzymes are stability and the activity of these enzymes. Probing the protein well-known. The ones most commonly used are entrapment structure by circular dichroism spectroscopy indicates that Teflon (i.e., in gels, semipermeable membranes, or vesicles), adpromotes the formation of helical structure in a-chymotrypsin, sorption (via e.g., hydrophobic and ionic interactions), and but the reverse effect is found with cutinase. The perturbed protein covalent binding (i.e., formation of a covalent bond between structures on Teflon are remarkably stable, showing no heat-induced structural transitions up to 100ЊC, as monitored by differen-the enzyme and the support material via an activating agent tial scanning calorimetry. Contact with the hydrophilic silica sursuch as glutaraldehyde). Among them, immobilization by face leads to a loss in the helix content of both proteins. Differential physical adsorption is the simplest method and is certainly scanning calorimetry points to a heterogeneous population of adthe method which offers the mildest experimental conditions sorbed protein molecules with respect to their conformational for obtaining an enzyme-particle complex. We used physistates. The fraction of the native-like conformation in the adsorbed cal adsorption to bind a-chymotrypsin and cutinase molelayer increases with increasing coverage of the silica surface by cules to the various support materials. the proteins. The specific enzymatic activity in the adsorbed state Because of the types of forces involved in the physical qualitatively correlates with the fraction of proteins in the nativeadsorption of enzymes onto solids, parameters such as pH, like conformation. ᭧ 1997 Academic Press ionic strength, and temperature must be controlled. Likewise, Key Words: a-chymotrypsin; cutinase; silica; Teflon; thermal the nature of the enzyme and of the support influence both denaturation; enzymatic activity; protein conformation. the amount adsorbed and the activity of the complex formed. It is widely reported in literature that hydrophobic interactions constitute a strong driving force for protein adsorption 437

Nanometre-sized inorganic dots, wires and belts have a wide range of electrical and optical properties, and variable mechanical stability and phase-transition mechanisms that show a sensitive dependency on size, shape and structure. The optical properties of the semiconductor ZnS in wurtzite structures are considerably enhanced, but the lack of structural stability limits technological applications. Here, we demonstrate that morphology-tuned wurtzite ZnS nanobelts show a particular low-energy surface structure dominated by the ±{210} surface facets. Experiments and calculations show that the morphology of ZnS nanobelts leads to a very high mechanical stability to ∼6.8 GPa, and also results in an explosive mechanism for the wurtzite-to-sphalerite phase transformation together with in situ fracture of the nanobelts. ZnS wurtzite nanobelts provide a model that is useful not only for understanding the morphology-tuned stability and transformation mechanism, but also for improving synthesis of metastable nanobelts with quantum effects for electronic and optical devices. Z nS has been extensively investigated as an important wideband-gap semiconductor (3.6 eV). It is one of the oldest and probably one of the most important materials in the electronics industry with a wide range of applications including light-emitting diodes and efficient phosphors in flatpanel displays 1 . An assortment of luminescent properties excited by ultraviolet, X-ray, cathode ray or electrical currents have been observed by doping ZnS with various metals 2 . Excellent light transmission with a high index of refraction (2.27 at 1 μm) also makes ZnS useful in photonic crystal devices that operate in the region from visible to near-infrared 3 .

Aerobic granulation is drawing increasing global interest in a quest for an efficient and innovative technology in wastewater treatment. Developed less than two decades ago, extensive research work on aerobic granulation has been reported. The instability of the granule, which is one of the main problems that hinder practical application of aerobic granulation technology, is still to be resolved. This paper presents a review of the literature in aerobic granulation focusing on factors that influence granule formation, granule development and their stability in the context of sludge granulation. The review attempts to shed light on the potential of developing granules with adequate structural stability for practical applications. The possibilities and perspective of using stored granule as inoculums for rapid startup, and as microbial supplement to enhance treatment of bioreactor systems are also discussed.

In Brazil, no tillage (NT) is a soil conservation practice now widely adopted by farmers, including smallholders. The effect of NT and conventional tillage (disc ploughing followed by two light disc harrowings, CT) was investigated on the aggregation properties of a clayey Rhodic Ferralsol from southern Brazil under different crop rotations. The same soil type under secondary forest was used as reference. Macro-and microaggregate classes were separated by wet sieving using a series of eight sieves (8, 4, 2, 1, 0.5, 0.25, 0.125, 0.053 mm) at four sampling layers (0-5, 5-10, 10-20, 20-30 cm). The soil in general had high structural stability. At 0-5 cm, meanweight diameter (MWD, 11.1 mm) and total organic C in macroaggregates (TOC, 39 g kg −1 soil) were highest for the forest soil. Soil under NT had a more similar distribution of aggregate size classes and TOC to the forest soil than CT. The most pronounced difference between tillage systems was observed in the surface soil layer (0-5 cm). In this layer, NT had higher aggregate stability (AS NT : 96%; AS CT : 89%), had higher values of aggregate size distribution (MWD NT : 7.9 mm, MWD CT : 4.3 mm), and had on average 28% greater TOC in all aggregate size classes than CT. Soil under NT had greater TOC in macroaggregates (NT: 22 g kg −1 ; CT: 13 g kg −1 ). Crop rotation did not have a significant effect on soil aggregate distribution and TOC. By increasing macroaggregation NT increased organic carbon accumulation in soil.

We develop a statistical thermodynamic model for the phase evolution of DNA-cationic lipid complexes in aqueous solution, as a function of the ratios of charged to neutral lipid and charged lipid to DNA. The complexes consist of parallel strands of DNA intercalated in the water layers of lamellar stacks of mixed lipid bilayers, as determined by recent synchrotron x-ray measurements. Elastic deformations of the DNA and the lipid bilayers are neglected, but DNA-induced spatial inhomogeneities in the bilayer charge densities are included. The relevant nonlinear Poisson-Boltzmann equation is solved numerically, including self-consistent treatment of the boundary conditions at the polarized membrane surfaces. For a wide range of lipid compositions, the phase evolution is characterized by three regions of lipid to DNA charge ratio, : 1) for low , the complexes coexist with excess DNA, and the DNA-DNA spacing in the complex, d, is constant; 2) for intermediate , including the isoelectric point ϭ 1, all of the lipid and DNA in solution is incorporated into the complex, whose inter-DNA distance d increases linearly with ; and 3) for high , the complexes coexist with excess liposomes (whose lipid composition is different from that in the complex), and their spacing d is nearly, but not completely, independent of . These results can be understood in terms of a simple charging model that reflects the competition between counterion entropy and inter-DNA ( Ͻ 1) and interbilayer ( Ͼ 1) repulsions. Finally, our approach and conclusions are compared with theoretical work by others, and with relevant experiments.