ABSTRACT Amplification of light from reporter fluorophores is a promising strategy to further inc... more ABSTRACT Amplification of light from reporter fluorophores is a promising strategy to further increase the sensitivity of fluorescence based biosensing. One such enhancement system is metal induced fluorescence enhancement (MIFE). The enhanced fluorescence intensity due to the pres-ence of metal nanostructures makes it possible to detect much lower levers of proteins tagged with fluorescence molecules. This paper reports work undertaken on the emission enhancement possible from triangular elements in the bow-tie configuration. The results show that emission enhancement is possible over a long distance (∼ 50 nm).
The optical characteristics of silicon nanowires grown on Si layers on glass have been modeled us... more The optical characteristics of silicon nanowires grown on Si layers on glass have been modeled using the FDTD (Finite Difference Time Domain) technique and compared with experimental results. The wires were grown by the VLS (vapour-liquid-solid) method using Sn catalyst layers and exhibit a conical shape. The resulting measured and modeled absorption, reflectance and transmittance spectra have been investigated as a function of the thickness of the underlying Si layer and the initial catalyst layer, the latter having a strong influence on wire density. High levels of absorption (>90% in the visible wavelength range) and good agreement between the modeling and experiment have been observed when the nanowires have a relatively high density of ~4 wires/µm2. The experimental and modeled results diverge for samples with a lower density of wire growth. The results are discussed along with some implications for solar cell fabrication.
We have fabricated and measured a high-capacity superconducting current lead composed ofa YiBa2Cu... more We have fabricated and measured a high-capacity superconducting current lead composed ofa YiBa2Cu307_x cylinder, 20 cm long and 0.9 cm 2 cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2 x 10-7 V/cm (p = 8 x 10-1~ ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y1Ba2Cu307_x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.
IEE Seminar Microwave Filters and Multiplexers, 2000
We study the influence of low levels of metal enrichment on the cooling and collapse of ionized g... more We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations. Our initial conditions represent protogalaxies forming within a fossil H ii region, a previously ionized H ii region which has not yet had time to cool and recombine. Prior to cosmological reionization, such regions should be relatively common, since the characteristic lifetimes of the likely ionizing sources are significantly shorter than a Hubble time. We show that in these regions, H 2 is the dominant and most effective coolant, and that it is the amount of H 2 formed that determines whether or not the gas can collapse and form stars. At the low metallicities (Z < 10 −3 Z ⊙) thought to be associated with the transition from Population III to early Population II star formation, metal-line cooling has an almost negligible effect on the evolution of low-density gas, altering the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm −3 and temperatures above 2000 K. Although there is evidence that metal-line cooling becomes more effective at higher density, we find no significant differences in behaviour from the metal-free case at any density below our sink particle creation threshold at n = 500 cm −3. Increasing the metallicity also increases the importance of metal-line cooling, but it does not significantly affect the dynamical evolution of the low-density gas
Table 1 Chemical analyses (ppm) of aluminium oxide powder used Several binders have been evaluate... more Table 1 Chemical analyses (ppm) of aluminium oxide powder used Several binders have been evaluated to determine their eVect on high frequency dielectric loss. Alumina cer-Impurity Na 2 O MgO SiO 2 Fe 2 O 3 CaO SO 3 CuO amics have been powder pressed with diVerent binder levels, sintered, and then the dielectric loss (tan d= Abundance, 20 16 85 29 ... ... 13 Q−1) has been measured at approximately 9•5 GHz. ppm T he quality factor Q was determined and significant diVerences were observed between samples made with diVerent binders. T he diVerences are caused by the turer. There have been studies to indicate the effects of, for diVerent levels of residual porosity left by the diVerent example, oxygen deficiency on the Q factor,2 and of grain binders. In addition, diVerences in levels of impurities size on Q,3,4 but none has examined the effect of the binder in the binders may also influence Q. Selected samples itself on Q. In this study, several different binders have been were measured for green body strength as a function chosen and mixed with high purity alumina. Alumina is a of binder content. BCT /392 very useful material as it can have a very low dielectric loss5,6 and hence the effect of even minor impurities is
Solid-state masers, hitherto only functional at cryogenic temperatures within a magnetic field, h... more Solid-state masers, hitherto only functional at cryogenic temperatures within a magnetic field, have recently been shown to operate at room temperature and in the earth's field. One of the key components in the room-temperature solid-state maser that has been developed is a gain medium where the stimulated emission occurs. Unlike the ruby gain medium in conventional masers, the new gain medium is an organic semiconductor co-crystal produced from pentacene doped p-terphenyl. Its excited triplet sublevels are degenerated without applying any magnetic field. Moreover, the population inversion of the uppermost sublevel is very high, leading to higher photon emission at very low doping concentrations. This thesis describes the optimization of the pentacene doping concentration to provide a maximum gain output while maintaining a long relaxation time. Single crystals of pentacene doped p-terphenyl were grown via Bridgman-Stockbarger method at various concentrations. Physical and elect...
2005 Asia-Pacific Conference on Applied Electromagnetics
Tunable filters are desirable components for modern RF and microwave communication systems. It is... more Tunable filters are desirable components for modern RF and microwave communication systems. It is required that the subsystems be easily integrated, reconfigurable, reproducible and small. Microstrip filters are good candidates for meeting these requirements. These can be made tunable by using ferroelectric interdigital capacitors to couple half wavelength resonators and applying an electrostatic field using a DC voltage. Based on
Design principles of a new class of microwave thin film bulk acoustic resonators with multiband r... more Design principles of a new class of microwave thin film bulk acoustic resonators with multiband resonance frequency switching ability are presented. The theory of the excitation of acoustic eigenmodes in multilayer ferroelectric structures is considered, and the principle of selectivity for resonator with an arbitrary number of ferroelectric layers is formulated. A so called "criterion function" is suggested that allows to determine the conditions for effective excitation at one selected resonance mode with suppression of other modes. The proposed theoretical approach is verifiedusing thepreexisting experimental data published elsewhere. Finally, the possible application of the two ferroelectric layers structures for switchable microwave overtone resonators, binary and quadrature phase-shift keying modulators are discussed. These devices could play a pivotal role in the miniaturization of microwave front-end antenna circuits.
The other day I was discussing magnetic fields in superconductors with a friend of mine, a fellow... more The other day I was discussing magnetic fields in superconductors with a friend of mine, a fellow Scot as it happens. He knows a thing or two about critical currents and magnetic fields in these materials and was pointing out the huge differences in what is perceived to be a high magnetic field. To people working on superconducting quantum interference devices (SQUIDs), a few millitesla is a high field. However, those working on magnets consider 20–30 T to be high. It is therefore important for all of us working in superconductivity to understand exactly what each section of the community means when talking about high or low currents or fields. This book attempts to explain the issues in straightforward terms.
ABSTRACT Amplification of light from reporter fluorophores is a promising strategy to further inc... more ABSTRACT Amplification of light from reporter fluorophores is a promising strategy to further increase the sensitivity of fluorescence based biosensing. One such enhancement system is metal induced fluorescence enhancement (MIFE). The enhanced fluorescence intensity due to the pres-ence of metal nanostructures makes it possible to detect much lower levers of proteins tagged with fluorescence molecules. This paper reports work undertaken on the emission enhancement possible from triangular elements in the bow-tie configuration. The results show that emission enhancement is possible over a long distance (∼ 50 nm).
The optical characteristics of silicon nanowires grown on Si layers on glass have been modeled us... more The optical characteristics of silicon nanowires grown on Si layers on glass have been modeled using the FDTD (Finite Difference Time Domain) technique and compared with experimental results. The wires were grown by the VLS (vapour-liquid-solid) method using Sn catalyst layers and exhibit a conical shape. The resulting measured and modeled absorption, reflectance and transmittance spectra have been investigated as a function of the thickness of the underlying Si layer and the initial catalyst layer, the latter having a strong influence on wire density. High levels of absorption (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;90% in the visible wavelength range) and good agreement between the modeling and experiment have been observed when the nanowires have a relatively high density of ~4 wires/µm2. The experimental and modeled results diverge for samples with a lower density of wire growth. The results are discussed along with some implications for solar cell fabrication.
We have fabricated and measured a high-capacity superconducting current lead composed ofa YiBa2Cu... more We have fabricated and measured a high-capacity superconducting current lead composed ofa YiBa2Cu307_x cylinder, 20 cm long and 0.9 cm 2 cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2 x 10-7 V/cm (p = 8 x 10-1~ ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y1Ba2Cu307_x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.
IEE Seminar Microwave Filters and Multiplexers, 2000
We study the influence of low levels of metal enrichment on the cooling and collapse of ionized g... more We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations. Our initial conditions represent protogalaxies forming within a fossil H ii region, a previously ionized H ii region which has not yet had time to cool and recombine. Prior to cosmological reionization, such regions should be relatively common, since the characteristic lifetimes of the likely ionizing sources are significantly shorter than a Hubble time. We show that in these regions, H 2 is the dominant and most effective coolant, and that it is the amount of H 2 formed that determines whether or not the gas can collapse and form stars. At the low metallicities (Z < 10 −3 Z ⊙) thought to be associated with the transition from Population III to early Population II star formation, metal-line cooling has an almost negligible effect on the evolution of low-density gas, altering the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm −3 and temperatures above 2000 K. Although there is evidence that metal-line cooling becomes more effective at higher density, we find no significant differences in behaviour from the metal-free case at any density below our sink particle creation threshold at n = 500 cm −3. Increasing the metallicity also increases the importance of metal-line cooling, but it does not significantly affect the dynamical evolution of the low-density gas
Table 1 Chemical analyses (ppm) of aluminium oxide powder used Several binders have been evaluate... more Table 1 Chemical analyses (ppm) of aluminium oxide powder used Several binders have been evaluated to determine their eVect on high frequency dielectric loss. Alumina cer-Impurity Na 2 O MgO SiO 2 Fe 2 O 3 CaO SO 3 CuO amics have been powder pressed with diVerent binder levels, sintered, and then the dielectric loss (tan d= Abundance, 20 16 85 29 ... ... 13 Q−1) has been measured at approximately 9•5 GHz. ppm T he quality factor Q was determined and significant diVerences were observed between samples made with diVerent binders. T he diVerences are caused by the turer. There have been studies to indicate the effects of, for diVerent levels of residual porosity left by the diVerent example, oxygen deficiency on the Q factor,2 and of grain binders. In addition, diVerences in levels of impurities size on Q,3,4 but none has examined the effect of the binder in the binders may also influence Q. Selected samples itself on Q. In this study, several different binders have been were measured for green body strength as a function chosen and mixed with high purity alumina. Alumina is a of binder content. BCT /392 very useful material as it can have a very low dielectric loss5,6 and hence the effect of even minor impurities is
Solid-state masers, hitherto only functional at cryogenic temperatures within a magnetic field, h... more Solid-state masers, hitherto only functional at cryogenic temperatures within a magnetic field, have recently been shown to operate at room temperature and in the earth's field. One of the key components in the room-temperature solid-state maser that has been developed is a gain medium where the stimulated emission occurs. Unlike the ruby gain medium in conventional masers, the new gain medium is an organic semiconductor co-crystal produced from pentacene doped p-terphenyl. Its excited triplet sublevels are degenerated without applying any magnetic field. Moreover, the population inversion of the uppermost sublevel is very high, leading to higher photon emission at very low doping concentrations. This thesis describes the optimization of the pentacene doping concentration to provide a maximum gain output while maintaining a long relaxation time. Single crystals of pentacene doped p-terphenyl were grown via Bridgman-Stockbarger method at various concentrations. Physical and elect...
2005 Asia-Pacific Conference on Applied Electromagnetics
Tunable filters are desirable components for modern RF and microwave communication systems. It is... more Tunable filters are desirable components for modern RF and microwave communication systems. It is required that the subsystems be easily integrated, reconfigurable, reproducible and small. Microstrip filters are good candidates for meeting these requirements. These can be made tunable by using ferroelectric interdigital capacitors to couple half wavelength resonators and applying an electrostatic field using a DC voltage. Based on
Design principles of a new class of microwave thin film bulk acoustic resonators with multiband r... more Design principles of a new class of microwave thin film bulk acoustic resonators with multiband resonance frequency switching ability are presented. The theory of the excitation of acoustic eigenmodes in multilayer ferroelectric structures is considered, and the principle of selectivity for resonator with an arbitrary number of ferroelectric layers is formulated. A so called "criterion function" is suggested that allows to determine the conditions for effective excitation at one selected resonance mode with suppression of other modes. The proposed theoretical approach is verifiedusing thepreexisting experimental data published elsewhere. Finally, the possible application of the two ferroelectric layers structures for switchable microwave overtone resonators, binary and quadrature phase-shift keying modulators are discussed. These devices could play a pivotal role in the miniaturization of microwave front-end antenna circuits.
The other day I was discussing magnetic fields in superconductors with a friend of mine, a fellow... more The other day I was discussing magnetic fields in superconductors with a friend of mine, a fellow Scot as it happens. He knows a thing or two about critical currents and magnetic fields in these materials and was pointing out the huge differences in what is perceived to be a high magnetic field. To people working on superconducting quantum interference devices (SQUIDs), a few millitesla is a high field. However, those working on magnets consider 20–30 T to be high. It is therefore important for all of us working in superconductivity to understand exactly what each section of the community means when talking about high or low currents or fields. This book attempts to explain the issues in straightforward terms.
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