Conditional Expectation

A concept study devised for the development of a biological containment system has been conducted. We show that the lysis genes of different phage origin function in a variety of bacteria. They may therefore be suited for conditional suicide cassettes. Moreover, we tested whether the Escherichia cofi rrnB Pl promoter could function as an environmentally responsive element sensing poor growth conditions expected after an accidental release of E. coli production strains from a bioreactor. Mimicking poor nutrient conditions by production of the alarmone guanosine tetraphosphate (ppGpp) with a plasmid encoded ppGpp synthetase I, the rmB Pl promoter activity was completely turned off. These experiments suggested that the rrnB Pl promoter may be used as an efficient biosensor for altered growth conditions.

Unlike the value at risk, the expected shortfall is a coherent measure of risk. In this paper, we discuss estimation of the expected shortfall of a random variable Y t with special reference to the case when auxiliary information is available in the form of a set of predictors X t. We consider three classes of estimators of the conditional expected shortfall of Y t given X t : a class of fully non-parametric estimators and two classes of analog estimators based, respectively, on the empirical conditional quantile function and the empirical conditional distribution function. We study their sampling properties by means of a set of Monte Carlo experiments and analyze their performance in an empirical application to financial data.

When listening to speech under adverse conditions, expectancies resulting from semantic context can have a strong impact on comprehension. Here we ask how minimal variations in semantic context (cloze probability) affect the unfolding comprehension of acoustically degraded speech. Three main results are observed in the brain electric response. First, auditory evoked responses to a degraded sentence's onset (N100) correlate with participants' comprehension scores, but are generally more vigorous for more degraded sentences. Second, a pronounced N400 in response to low-cloze sentence-final words, reflecting the integration effort of words into context, increases linearly with improving speech intelligibility. Conversely, transient enhancement in Gamma band power (γ,~40-70 Hz) during high-cloze sentence-final words (~600 ms) reflects top-down-facilitated integration. This γ-band effect also varies parametrically with signal quality. Third, a negative correlation of N100 amplitude at sentence onset and the later γ-band response is found in moderately degraded speech. This reflects two partly distinct neural strategies when dealing with moderately degraded speech; a more "bottom-up," resource-allocating, and effortful versus a more "top-down," associative and facilitatory strategy. Results also emphasize the non-redundant contributions of phase-locked (evoked) and non-phase-locked (induced) oscillatory brain dynamics in auditory EEG.

This paper focuses on the problem of Kalman filtering for Itô stochastic continuous-time systems with multiple delayed measurements, for which very little work exist to date. For an Itô-stochastic system, its stochastic differential and integral have a significant place and are different from other stochastic systems owing to the Wiener or the Brownian process. In this paper, an Itô stochastic continuous-time system with multiple delayed measurements is first reduced to a system with delay free measurements by applying the stochastic analysis and calculus of stochastic variables. Next, the Itô differentials for the optimal filter and its error variance are derived. Finally, through an illustrative example, the performance of the designed optimal filter is verified.

En este artículo se presenta evidencia en relación al número de tendencias comunes estocásticas existentes en tres monedas representativas del ERM. Los resultados obtenidos indican la presencia de una única tendencia común para dichos tipos de cambio. Dicha tendencia común puede ser interpretada como los fundamentos no paramétricos de dichas monedas dentro del ERM, lo cual indica que en un sistema cambiario como el Sistema Monetario Europeo los tipos de cambio tienen que ser modelizados de forma conjunta. Usando una técnica no paramétrica, el algoritmo ACE (Expectativas Condicionales Alternativas), obtenemos evidencia de la existencia de no-linealidades para dos de las tres monedas analizadas, con una forma funcional, relativa a los fundamentos no paramétricos estimados, similar a la forma en S que se obtiene a partir del modelo básico de zonas objetivo.

We compare capital requirements derived by tail conditional expectation (TCE) with those derived by tail conditional median (TCM) and find that there is no clear-cut relationship between these two measures in empirical data. Our results highlight the relevance of TCM as a robust alternative to TCE, especially for regulatory control.

The EM algorithm is a popular and useful algorithm for "nding the maximum likelihood estimator in incomplete data problems. Each iteration of the algorithm consists of two simple steps: an E-step, in which a conditional expectation is calculated, and an M-step, where the expectation is maximized. In some problems, however, the EM algorithm cannot be applied since the conditional expectation required in the E-step cannot be calculated. Instead the expectation may be estimated by simulation. We call this a simulated EM algorithm. The simulations can, at least in principle, be done in two ways. Either new independent random variables are drawn in each iteration, or the same uniforms are re-used in each iteration. In this paper the properties of these two versions of the simulated EM algorithm are discussed and compared.

The use of placebo may have accompanied healing and medical practices since their origins (Plato; Charmides, 155-156). Recent experimental data indicate that we would be well advised to further consider placebo eVects in future therapeutic strategies, with a better knowledge of their potency, psychological basis and underlying neurobiological mechanisms. Current research in the areas of pain, depression and Parkinson's disease has uncovered some of the potential neurobiological mechanisms of placebo eVects. These data indicate that conscious expectation and unconscious behavioral conditioning processes appear to be the major neurobiological mechanisms capable of releasing endogenous neurotransmitters and/or neurohormones that mimic the expected or conditioned pharmacological eVects. To date, research on placebo responses aVecting immune-related diseases is scarce, but there are consistent indications that skin and mucosal inXammatory diseases, in particular, are strongly modulated by placebo treatments. However, the brain's capability to modulate peripheral immune reactivity has been impressively demonstrated by paradigms of behavioral conditioning in animal experiments and human studies. Thus, placebo eVects can beneWt end organ functioning and the overall health of the individual through positive expectations and behavioral conditioning processes.

A self-consistent description (performed by means of the B2-EIRENE code package) of a hydrogen plasma including electrons, ions and neutral background gas is used to investigate the processes and plasma behavior under conditions expected in MAGNUM-PSI. Several cases varying in gas-puffing, pumping rate, and plasma parameters are simulated. In all cases a detached plasma regime is achieved. The plasma density increases considerably for higher neutral pressures up to (1-5) · 10 14 cm À3 . The particle flux to the target is $10 24 m À2 s À1 and the plasma heat flux is $10 MW m À2 . The latter is significantly reduced in front of the target due to electron and ion cooling resulting from ionization and dissociation of H 2 molecules, and charge exchange/elastic collisions. Under the conditions of investigation, the losses due to molecule activated recombination are dominant compared with 3-body recombination of atomic ions.

h o striking contributions of BienaymC to mathematical statistics: (1) a completely correct statement of the Criticality Theorem for simple branching processes in 1845; and (2) the derivation of the Bienaymb Chebyshev Inequality, are revisited on the 200th anniversary of his birth. We use writings and archival materials available since the note of Heyde & Seneta (1972) to present a fuller biographical picture. BienaymC's connections with Buniakovsky and Chebyshev are elucidated, and his role in furthering Chebyshev's international contacts outlined. A concluding section illuminates Bienaymk's understanding of the linear regression of one random variable on another in an actuarial context of random shocks.

This paper considers the stochastic cash balance problem. A dynamic simple policy (DSP) is proposed to minimise transaction costs, under a general cost structure, when the cash flows are not independently or identically distributed. The validity of the approach is demonstrated using the scenario of double exponentially distributed cash flows considered by Penttinen. A data set from a large multinational is used to demonstrate the practical application of the DSP. To provide conditional expectations of future cash flows, a time series model is developed to provide forecasts. The performance of the DSP on these cash flows achieved a 16% saving in average transaction cost (over the Penttinen model). The saving due to the forecasting model over the assumption that the cash flows exhibit a constant mean is a function of the time series structure of the relevant cash flows. For the example data, the benefit of using the bespoke forecasting model over the constant mean was only 2%.

Carbon emissions related to human activities have been significantly contributing to the elevation of atmospheric [CO 2 ] and temperature. More recently, carbon emissions have greatly accelerated, thus much stronger effects on crops are expected. Here, we revise literature data concerning the physiological effects of CO 2 enrichment and temperature rise on crop species. We discuss the main advantages and limitations of the most used CO 2 -enrichment technologies, the Open-Top Chambers (OTCs) and the Free-Air Carbon Enrichment (FACE). Within the conditions expected for the next few years, the physiological responses of crops suggest that they will grow faster, with slight changes in development, such as flowering and fruiting, depending on the species. There is growing evidence suggesting that C 3 crops are likely to produce more harvestable products and that both C 3 and C 4 crops are likely to use less water with rising atmospheric [CO 2 ] in the absence of stressful conditions. However, the beneficial direct impact of elevated [CO 2 ] on crop yield can be offset by other effects of climate change, such as elevated temperatures and altered patterns of precipitation. Changes in food quality in a warmer, high-CO 2 world are to be expected, e.g., decreased protein and mineral nutrient concentrations, as well as altered lipid composition. We point out that studies related to changes in crop yield and food quality as a consequence of global climatic changes should be priority areas for further studies, particularly because they will be increasingly associated with food security.

The aim of this paper is to present a self-contained introduction to the theory of martingales of random sets (also called &set-valued martingales' or &multivalued martingales'). For this purpose, we "rst present a method for constructing the integral and the conditional expectation for random sets with compact convex values in RB. This method was used by Debreu for constructing the set-valued integral. It is based on the approximation of random sets by simple random sets, i.e., assuming only a "nite number of values. It allows us to recover the classical properties of the conditional expectation of real-valued random variables and to deduce new applications, such as an extension of the Brunn-Minkowski inequality. Afterwards, multivalued martingales are introduced, as well as multivalued submartingales and supermartingales. We prove several convergence results, and we give examples and applications. Further, strong laws of large numbers for sequences of independent random sets with compact values are brie#y examined. Another approach for de"ning the integral and the conditional expectation of random sets is also sketched, and an existence theorem for martingale selections is stated. The last section is devoted to the de"nition of the integral for non convex random sets. Finally, in a short annex, we present a criterion for the conditional expectation of a random set to be singlevalued.

These lecture notes codify extensive recent research on economic forecasting. When a forecast- ing model coincides with the mechanism generating the data (DGP) in an unchanging world, the theory of economic forecasting is well developed. Forecasts are the conditional expectation, are un- biased, and no other predictor has a smaller mean-square forecast error matrix. Cointegration does not markedly alter that

Distribution of some statistics, especially rank based, with censored data are hard to get. Even if they can be worked out for small samples, they are likely to be prohibitively expensive for larger sample sizes. Therefore we need to work on the asymptotic distribution - which often works well for moderate and large sample sizes. This notes is intended to

In this paper, we apply the Jensen's inequality to derive sharp lower and upper bounds for conditional expectations of multiplicative functionals of diffusion processes. We show that the bounds are applicable to the pricing of European-style derivative securities. We also adapt the method to price (double) barrier options and lookback options under local volatility models. As by-product result, we propose a static hedge for lookback options. Numerical illustrations performed for the CEV model demonstrate the high accuracy of the method.

This paper considers the stochastic cash balance problem. A dynamic simple policy (DSP) is proposed to minimise transaction costs, under a general cost structure, when the cash flows are not independently or identically distributed. The validity of the approach is demonstrated using the scenario of double exponentially distributed cash flows considered by Penttinen. A data set from a large multinational is used to demonstrate the practical application of the DSP. To provide conditional expectations of future cash flows, a time series model is developed to provide forecasts. The performance of the DSP on these cash flows achieved a 16% saving in average transaction cost (over the Penttinen model). The saving due to the forecasting model over the assumption that the cash flows exhibit a constant mean is a function of the time series structure of the relevant cash flows. For the example data, the benefit of using the bespoke forecasting model over the constant mean was only 2%.

Complexity is an interdisciplinary program publishing the best research and academiclevel teaching on both fundamental and applied aspects of complex systems -cutting across all traditional disciplines of the natural and life sciences, engineering, economics, medicine, neuroscience, social and computer science.

Existence, $L^2$-stationarity and linearity of conditional expectations $\wwo{X_k}{...,X_{k-2},X_{k-1}}$ of square integrable random sequences $\mathbf{X}=(X_{k})_{k\in\mathbb{Z}}$ satisfying \[ \wwo{X_k}{...,X_{k-2},X_{k-1},X_{k+1},X_{k+2},...}=\sum_{j=1}^\infty b_j(X_{k-j}+X_{k+j}) \] for a real sequence $(b_n)_{n\in\nat}$, is examined. The analysis is reliant upon the use of Laurent and Toeplitz operator techniques.

As more firms begin to collect (and seek value from) richer customer-level datasets, a focus on the emerging concept of customer-base analysis is becoming increasingly common and critical. Such analyses include forward-looking projections ranging from aggregate-level sales trajectories to individual-level conditional expectations (which, in turn, can be used to derive estimates of customer lifetime value). We provide an overview of a class of parsimonious models (called probability models) that are well-suited to meet these rising challenges. We first present a taxonomy that captures some of the key distinctions across different kinds of business settings and customer relationships, and identify some of the unique modeling and measurement issues that arise across them. We then provide deeper coverage of these modeling issues, first for noncontractual settings (i.e., situations in which customer "death" is unobservable), then contractual ones (i.e., situations in which customer "death" can be observed). We review recent literature in these areas, highlighting substantive insights that arise from the research as well as the methods used to capture them. We focus on practical applications that use appropriately chosen data summaries (such as recency and frequency) and rely on commonly available software packages (such as Microsoft Excel).

We develop a new solution method for a broad class of discrete-time dynamic portfolio choice problems. The method efficiently approximates conditional expectations of the value function by using (i) a decomposition of the state variables into a component observable by the investor and a stochastic deviation; and (ii) a Taylor expansion of the value function. We illustrate the accuracy of the method in handling several realistic features of portfolio choice problems such as intermediate consumption, multiple assets, multiple state variables, portfolio constraints, non-time-separable preferences, and nonredundant endogenous state variables. We finally use the method to solve a realistic large-scale life-cycle portfolio choice and consumption problem with predictable expected returns and recursive preferences. (JEL G11, G12) Since the seminal work of and , the study of portfolio formation and management for long-lived investors has enjoyed a rich and celebrated history in the financial economics literature. With a few notable exceptions, 1 the vast majority of realistic dynamic portfolio choice problems are analytically intractable, and their solution typically relies on complex numerical procedures. The computationally intensive nature of existing numerical methods restricts the range of potential applications ). 1 Obtaining a fully closed-form solution to a portfolio choice/consumption problem typically requires particular assumptions about preferences, market completeness, and absence of frictions and constraints. Examples of papers that derive closed-form solutions include Kim at University of British Columbia on October 7, 2010 rfs.oxfordjournals.org Downloaded from The Review of Financial Studies / v 23 n 9 2010 4 at University of British Columbia on October 7, 2010 rfs.oxfordjournals.org Downloaded from The Review of Financial Studies / v 23 n 9 2010 9 at University of British Columbia on October 7, 2010 rfs.oxfordjournals.org Downloaded from

Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO 2 ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO 2 partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900°C. At CO 2 concentrations of 80-85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800°C with CO 2 concentration set at 80% and H 2 O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H 2 O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400°C < T 6 800°C, the higher the temperature the higher the CaOto-carbonate conversion ratio. The presence of H 2 O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H 2 O. For T 6 400°C, no fly ash carbonation occurred without the presence of H 2 O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250°C. For T 6 300°C, small amounts of Ca(OH) 2 were found in the final product alongside CaCO 3 . Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined.

In all species, sexual behavior is directed by a complex interplay between steroid hormone actions in the brain that give rise to sexual arousability and experience with sexual reward that gives rise to expectations of competent sexual activity, including sexual arousal, desire, and performance. Sexual experience allows animals to form instrumental and Pavlovian associations that predict sexual outcome and thereby directs the strength of sexual responding. Although the study of animal sexual behavior by neuroendocrinologists has traditionally been concerned with mechanisms of copulatory responding, more recent use of conditioning and preference paradigms, and a focus on environmental circumstances and experience, has revealed behaviors and processes that resemble human sexual responses. In this paper, we review behavioral paradigms used with rodents and other species that are analogous or homologous to human sexual arousal, desire, reward, and inhibition. The extent to which these b...

Not only are copula functions joint distribution functions in their own right, they also provide a link between multivariate distributions and their lower-dimensional marginal distributions. Copulas have a structure that allows us to characterize all possible multivariate distributions, and therefore they have the potential to be a very useful statistical tool. Although copulas can be traced back to 1959, there is still much scope for new results, as most of the early work was theoretical rather than practical. We focus on simple practical tools based on conditional expectation, because such tools are not widely available. When dealing with data sets in which the dependence throughout the sample is variable, we suggest that copula-based regression curves may be more accurate predictors of specific outcomes than linear models. We derive simple conditional expectation formulae in terms of copulas and apply them to a combination of simulated and real data.

This paper investigates weak convergence of U -statistics via approximation in probability. The classical condition that the second moment of the kernel of the underlying U -statistic exists is relaxed to having 4 3 moments only (modulo a logarithmic term). Furthermore, the conditional expectation of the kernel is only assumed to be in the domain of attraction of the normal law (instead of the classical two-moment condition). * Research supported by a Carleton university Faculty of Graduate Studies and Research scholarship, and NSERC Canada Discovery Grants of M. Csörgő and M. Mojirsheibani at Carleton university.

Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO 2 ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO 2 partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900°C. At CO 2 concentrations of 80-85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800°C with CO 2 concentration set at 80% and H 2 O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H 2 O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400°C < T 6 800°C, the higher the temperature the higher the CaOto-carbonate conversion ratio. The presence of H 2 O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H 2 O. For T 6 400°C, no fly ash carbonation occurred without the presence of H 2 O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250°C. For T 6 300°C, small amounts of Ca(OH) 2 were found in the final product alongside CaCO 3 . Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined.

Numerous studies along the northern Mediterranean borderland have documented the use of shellfish by Neanderthals but none of these finds are prior to Marine Isotopic Stage 3 (MIS 3). In this paper we present evidence that gathering and consumption of mollusks can now be traced back to the lowest level of the archaeological sequence at Bajondillo Cave (Málaga, Spain), dated during the MIS 6. The paper describes the taxonomical and taphonomical features of the mollusk assemblages from this level Bj 19 and briefly touches upon those retrieved in levels Bj 18 (MIS 5) and Bj 17 (MIS 4), evidencing a continuity of the shellfishing activity that reaches to MIS 3. This evidence is substantiated on 29 datings through radiocarbon, thermoluminescence and U series methods. Obtained dates and paleoenvironmental records from the cave include isotopic, pollen, lithostratigraphic and sedimentological analyses and they are fully coherent with paleoclimate conditions expected for the different stages. We conclude that described use of shellfish resources by Neanderthals (H. neanderthalensis) in Southern Spain started ,150 ka and were almost contemporaneous to Pinnacle Point (South Africa), when shellfishing is first documented in archaic modern humans. Citation: Cortés-Sánchez M, Morales-Muñ iz A, Simó n-Vallejo MD, Lozano-Francisco MC, Vera-Peláez JL, et al. (2011) Earliest Known Use of Marine Resources by Neanderthals. PLoS ONE 6(9): e24026.

We introduce a new class of graphical representations, expected utility networks (EUNs), and discuss some of its properties and potential applications to artificial intelligence and economic theory. In EUNs not only probabilities, but also utilities enjoy a modular representation. EUNs are undirected graphs with two types of arc, representing probability and utility dependencies respectively. The representation of utilities is based on a novel notion of conditional utility independence, which we introduce and discuss in the context of other existing proposals. Just as probabilistic inference involves the computation of conditional probabilities, strategic inference involves the computation of conditional expected utilities for alternative plans of action. We define a new notion of conditional expected utility (EU) independence, and show that in EUNs node separation with respect to the probability and utility subgraphs implies conditional EU independence.

Let 1 ≤ p < ∞ and (x n) n∈N be a sequence of positive elements in a noncommutative L p space and (E n) n∈N be an increasing sequence of conditional expectations, then n E n (x n) p ≤ c p n x n p. This inequality is due to Burkholder, Davis and Gundy in the commutative case. By duality, we obtain a version of Doob's maximal inequality for 1 < p ≤ ∞.

Abstract. We present simple and fast algorithms for computing very tight upper and lower bounds on the prices of American Asian options in the binomial model. We introduce a new refined version of the Cox-Ross-Rubinstein (1979) binomial lattice of stock prices. Each node in the ...

In this paper we extend previous results of Banach, Lamperti and Yeadon on isometries of Lp-spaces to the non-tracial case first introduced by Haagerup. Specifically, we use operator space techniques and an extrapolation argument to prove that every 2-isometry T : Lp(M) to Lp(N) between arbitrary noncommutative Lp-spaces can always be written in the form T(phi^1/p) = w (phi circ pi^-1 circ E)^1/p, for phi in M_*^+. Here pi is a normal *-isomorphism from M onto the von Neumann subalgebra pi(M) of N, w is a partial isometry in N, and E is a normal conditional expectation from N onto pi(M). As a consequence of this, any 2-isometry is automatically a complete isometry and has completely contractively complemented range.

In this paper, we propose a novel approach to econometric forecasting of stationary and ergodic time series within a panel-data framework. Our key element is to employ the (feasible) bias-corrected average forecast. Using panel-data sequential asymptotics we show that it is potentially superior to other techniques in several contexts. In particular, it is asymptotically equivalent to the conditional expectation, i.e., has an optimal limiting mean-squared error. We also develop a zeromean test for the average bias and discuss the forecast-combination puzzle in small and large samples. Monte-Carlo simulations are conducted to evaluate the performance of the feasible bias-corrected average forecast in …nite samples. An empirical exercise based upon data We are especially grateful for the comments and suggestions given by two anonymous referees,

Let (Ω, F , P ) be a probability space. For each G ⊂ F , define G as the σ-field generated by G and those sets F ∈ F satisfying P (F ) ∈ {0, 1}. Conditions for P to be atomic on ∩ k i=1 A i , with A 1 , . . . , A k ⊂ F sub-σ-fields, are given. Conditions for P to be 0-1-valued on ∩ k i=1 A i are given as well. These conditions are useful in various fields, including Gibbs sampling, iterated conditional expectations and the intersection property.

Middle Hettangian (Early Jurassic) plant macrofossils from the Kamishak Formation at Puale Bay, Alaska occur mainly as leaves and leafy shoots found together with ammonites that allow precise biostratigraphic age assignment. This new locality is the first in the Jurassic of Alaska where the plant material shows preserved cuticle. Four species of three genera are identified representing three different gymnosperm groups: Otozamites mimetes and O. tenuatus (Bennettitales), Brachyphyllum crucis (Coniferales), and Sagenopteris pualensis Barbacka n. sp. (Pteridospermophyta) which is described as new. Their macro-and micromorphology show xeromorphic characters that suggest either an arid environment or a habitat with soil of increased salinity. The latter inference is preferred because it is consistent with conditions expected on an oceanic island, the mode of preservation, and accompanying marine fossils. Adaptation to coastal habitats, possibly occupied by a halophytic, mangrove-type vegetation, is implied. The new species is thus far only known from Alaska whereas the three other taxa from Puale Bay also occur at a few localities of the Middle Jurassic in the UK but they are not known from any other areas. Paleoclimatic and paleogeographic implications of the Puale Bay flora help constrain models for the tectonic evolution of the Peninsular terrane. The paleobotanic evidence favors a low-latitude setting for the Early Jurassic Talkeetna volcanic island arc to which the Kamishak Formation belongs. Plant dispersal requires proximity of the Peninsular terrane to cratonic North America at least by Middle Jurassic time.

In the Central American Volcanic Arc, adakite-like volcanism has often been described as volumetrically insignificant. However, extensive silicic adakitic volcanism does occur in the Panamanian arc and provides an opportunity to evaluate the origin of this magma-type as well as to contrast its origin with other Central American silicic magmas. The Quaternary volcanic deposits of El Valle volcano are characterized by pronounced depletions in the heavy rare earth elements, low Y, high Sr, high Sr/Y, relatively high MgO, and low K2O/Na2O, when compared with other Quaternary Central American volcanics at similar SiO2. These chemical features are also diagnostic of adakitic signatures. Our new 40Ar/39Ar ages of lava flows and ash flows that compose the volcanic edifice of El Valle volcano illustrate that the eruptive volume of adakitic-like volcanism is substantial during the Quaternary (~120 km3). Adakitic-like magmas dominate the stratigraphic record. Common to all models for the origin of an adakite geochemical signature is the involvement of garnet, as a residual or fractionating phase. The stability of garnet in hydrous magmas has been recently reevaluated with important consequences; garnet is a stable primary igneous phase at pressure and temperature conditions expected for magma differentiation at the roots of a mature island arc. Moreover, adakite-like volcanism erupted at El Valle volcano displays the middle rare earth element depletion observed in other Panamanian volcanic centers that has been attributed to significant amphibole fractionation. Extensive amphibole fractionation may have occurred in two stages. The first stage of fractionation, garnet + amphibole fractionation, occurs from hydrous basaltic–andesitic parental magmas that have ponded at the base of an overthickened crust. The second stage occurs at mid-lower crustal levels where abundant amphibole + plagioclase and minor sphene crystallized from water-rich magmas. These two stages combined may have resulted in an amphibole-rich cumulate layer. This amphibole layer is likely the source of the abundant amphibole-rich cumulate enclaves and blobs found in volcanic products across the Panamanian arc. Stalling of water-rich magmas during this two-stage fractionation process could drive the interstitial liquids to the evolved compositions typical of continental crust, while leaving behind amphibole-rich cumulate rocks that may eventually be returned to the asthenosphere. Differentiation of H2O-rich magmas under the conditions appropriate for the roots of island arcs may therefore be a key process in developing a better understanding of the generation of continental crust in island arc environments.

When the assumption of constant risk premiums is relaxed, financial valuation models may be tested, and risk measures estimated without specifying a market index or state variables. This is accomplished by examining the behavior of conditional expected returns. The approach is developed using a single risk premium asset pricing model as an example and then extended to models with multiple risk premiums. The methodology is illustrated using daily return data on the common stocks of the Dow Jones 30. The tests indicate that these returns are consistent with a single, time-varying risk premium.