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Neuroscience initiatives aim to develop new technologies and tools to measure and manipulate neuronal circuits. To deal with the massive amounts of data generated by these tools, the authors envision the co-location of open data repositories in standardized formats together with high-performance computing hardware utilizing open source optimized analysis codes.

Managing marketing resources over time requires dynamic model estimation, which necessitates specifying some parametric or nonparametric probability distribution. When the data generating process differs from the assumed distribution, the resulting model is misspecified. To hedge against such a misspecification risk, the extant theory recommends using the sandwich estimator. This approach, however, only corrects the variance of estimated parameters, but not their values. Consequently, the sandwich estimator does not affect any managerial outcomes such as marketing budgeting and allocation decisions. To overcome this drawback, we present the minimax framework that does not necessitate distributional assumptions to estimate dynamic models. Applying minimax control theory, we derive an optimal robust filter, illustrate its application to a unique advertising data set from the Canadian Blood Services, and contribute several novel findings. We discover the compensatory effect: Advertising effectiveness increases and the carryover effect decreases as robustness increases. We also find that the robust filter uniformly outperforms the Kalman filter on the out-of-sample predictions. Furthermore, we uncover the existence of a profit-volatility trade-off, similar to the returns-risk trade-off in finance, whereby the volatility of profit stream decreases at the expense of reduced total profit as robustness increases. Finally, we prove that, unlike for-profit companies, managers of nonprofit organizations should optimally allocate budgets opposite the advertising-to-sales ratio heuristic; that is, advertise more (less) when sales are low (high).

The electronic band structure of Ga(PAsN) with a few percent of nitrogen is calculated in the whole composition range of Ga(PAs) host using density functional methods including the modified Becke-Johnson functional to correctly reproduce the bandgap and unfolding of the supercell band structure to reveal the character of the bands. Relatively small amounts of nitrogen introduced to Ga(PAs) lead to the formation of an intermediate band below the conduction band, which is consistent with the band anticrossing model, widely used to describe the electronic band structure of dilute nitrides. However, in this study, calculations are performed in the whole Brillouin zone and they reveal the significance of the correct description of the band structure near the edges of the Brillouin zone, especially for the indirect bandgap P-rich host alloy, which may not be properly captured with simpler models. The influence of nitrogen on the band structure is discussed in terms of the application of Ga(PAsN) in optoelectronic devices such as intermediate band solar cells, light emitters, as well as two color emitters. Additionally, the effect of nitrogen incorporation on the carrier localization is studied and discussed. The theoretical results are compared with experimental studies, confirming their reliability. [ABSTRACT FROM AUTHOR]

The dilute nitride (GaIn)(NAs) material system grown lattice matched to GaAs or Ge with a 1 eV band gap is an interesting material for the use in four-junction solar cells with increased efficiencies. As a result of its metastability, several challenges exist for this material system, which up to now limits the device performance. We performed nanostructural analysis in combination with photoluminescence characterization to optimize the metal organic vapor phase growth as well as the annealing conditions for the quaternary solar cell material. The optimum annealing conditions depend strongly on the In content of the quaternary material. Valence force field calculations of stable N environments in the alloy support the model that the N moves from a Ga rich environment realized during growth into an In rich environment upon annealing. Simultaneously, N induced strain fluctuations, which are detected in the N containing material upon growth, are dissolved and the device properties are improved. [DOI: 10.1115/1.2734568]

Impact ionization coefficient is a critical parameter that determines the multiplication gain in avalanche photodiodes. The impact ionization coefficient is closely related to the ionization threshold, [E.sub.th], which is determined by the band dispersion of the semiconducting material used in detectors. The ionization threshold energy is commonly calculated based on a parabolic band assumption, which provides only a crude approximation. Here we present a first principle study of the ionization threshold energy through an analysis of the electronic structure of trigonal selenium. It is shown that the excess energy of primary charge carriers required to initiate the impact ionization in trigonal selenium can be as low as the band gap, [E.sub.g], which is a sharp contrast to the parabolic band approximation that implies [E.sub.th] = 3/2[E.sub.g]. Such a low [E.sub.th] value is a favourable factor for impact ionization. PACS Nos.: 71.20.-b, 71.20.Mq, 73.50.Fq. Le coefficient d'ionisation par impact est un parametre critique qui determine le gain par multiplication dans l'avalanche d'une photodiode. Ce parametre est tres relie au seuil d'ionisation, [E.sub.th], qui est determine par la dispersion de bande du semi-conducteur utilise dans le detecteur. L'energie de seuil d'ionisation est generalement calculee en se basant sur une hypothese de bande parabolique, ce qui est une approximation grossiere. Nous presentons ici une etude a partir de principes premiers pour l'energie du seuil d'ionisation, via une analyse de la structure electronique du selenium trigonal. Nous montrons que l'exces d'energie des porteurs primaires de charge, requise pour initier l'ionisation par impact dans le selenium trigonal, peut etre aussi basse que la separation (gap) de bande [E.sub.g], ce qui est en contraste marque avec l'approximation parabolique qui implique [E.sub.th] = 3/2[E.sub.g]. Une aussi basse valeur pour [E.sub.th] favorise l'ionisation par impact. [Traduit par la Redaction], 1. Introduction Impact ionization and subsequent avalanche multiplication of charge carriers is widely studied in amorphous selenium-based (a-Se) avalanche photosensors, which have found an application in high-sensitivity photosensors for television [...]

Graphene Oxide (GO) has been shown to exhibit properties that are useful in applications such as biomedical imaging, biological sensors, and drug delivery. The binding properties of biomolecules at the surface of GO can provide insight into the potential biocompatibility of GO. Here we assess the intrinsic affinity of amino acids to GO by simulating their adsorption onto a GO surface. The simulation is done using Amber03 force-field molecular dynamics in explicit water. The emphasis is placed on developing an atomic charge model for GO. The adsorption energies are computed using atomic charges obtained from an ab initio electrostatic potential based method. The charges reported here are suitable for simulating peptide adsorption to GO. [ABSTRACT FROM AUTHOR]

A critical requirement for high gain and low noise avalanche photodiodes is the single-carrier avalanche multiplication. We propose that the single-carrier avalanche multiplication can be achieved in materials with a limited width of the valence band resulting in a restriction of kinetic energy for holes while allowing electrons to participate in the multiplication cascade. This feature of the electric structure is not common to the majority of technologically relevant semiconductors, but it can be anticipated in chalcopyrite Cu(AlGa)Se2 alloys based on the presented electric structure calculations. [ABSTRACT FROM AUTHOR]

Current-voltage characteristics of GaAs tunnel diodes are studied experimentally and theoretically. In theoretical calculations contributions of three different transport mechanisms are considered: direct tunneling processes, nonresonant multiphonon tunneling processes via defects, and resonant tunneling processes through defects. The comparison between theoretical results and experimental data reveals resonant tunneling as the dominant transport mechanism at voltages corresponding to the peak current. At higher voltages this mechanism is replaced by nonresonant tunneling, which is in its turn replaced by over-barrier transport at even larger voltages. [ABSTRACT FROM AUTHOR]

The blueshift of the fundamental energy gap of (GaIn)(NAs) upon thermal treatment is well established. However, the physical reason is still controversially discussed in literature. In the present paper we give direct structural evidence using transmission electron microscopy in combination with structure factor calculation that this blueshift—for the metal organic vapor phase epitaxy grown samples investigated here—results solely from a change in the local environment of nitrogen. N is bound to Ga upon growth and moves into an In-rich environment upon annealing to minimize the strain energy of the crystal. The technique presented here can be used to unambiguously determine the reason for the blueshift of differently grown and annealed dilute nitride materials. [ABSTRACT FROM AUTHOR]

III/V semiconductors containing dilute amounts of nitrogen are metastable and need to be thermally treated after growth to optimize optoelectronic properties. The influence of thermal annealing on the nitrogen depth profile in metal organic vapor phase epitaxygrown Ga(NAs)/GaAs as well as (GaIn)(NAs)/GaAs heterostructures is examined on a nanometer scale by combining several high resolution transmission electron microscopy techniques, also with Rutherford backscattering spectrometry. Annealing conditions, which are optimized for quaternary alloys with respect to photoluminescence intensity, do not result in element redistribution for the In containing material. Contrary to the quaternary material, the result of annealing the ternary Ga(NAs) is a pronounced pileup of the nitrogen profile without any out diffusion of nitrogen. These findings have important influence on device structures, which often contain Ga(NAs) barriers for strain-compensation purposes together with (GaIn)(NAs) active regions. In the light of metastability considerations for the ternary and quaternary alloy, one can conclude that the In contained in the quaternary material stabilizes the material and suppresses phase separation. Consequently (GaIn)(NAs) is more stable than its ternary counterpart Ga(NAs). [ABSTRACT FROM AUTHOR]

Although the effect of the impact ionization and the consequent avalanche multiplication in amorphous selenium (a-Se) was established long ago and has led to the development and commercialization of ultrasensitive video tubes, the underlying physics of these phenomena in amorphous semiconductors has not yet been fully understood. In particular, it is puzzling why this effect has been evidenced at practical electric fields only in a-Se among all amorphous materials. For instance, impact ionization seems much more feasible in hydrogenated amorphous silicon (a-Si:H) since the charge carrier mobility in a-Si:H is much higher than that in a-Se and also the amount of energy needed for ionization of secondary carriers in a-Si:H is lower than that in a-Se. Using the description of the avalanche effect based on the lucky-drift model recently developed for amorphous semiconductors we show how this intriguing question can be answered. It is the higher phonon energy in a-Si:H than that in a-Se, which is responsible for the shift of the avalanche threshold in a-Si:H to essentially higher fields as compared to a-Se. [ABSTRACT FROM AUTHOR]

The kinetics of the photodarkening effect has been studied experimentally for amorphous selenium (a-Se) layers at room temperature and at an elevated temperature (35 °C) close to the glass transition. By switching an intense pumping light on and off with a period of 100 s, we have studied the kinetics of both the buildup of photodarkening and its relaxation (recovery). It was found that at 35 °C, only a reversible component of photodarkening has been observed. This result has been interpreted within the framework of a phenomenological model assuming that photodarkening is caused by light-induced transitions of structural units from their ground states into metastable states. Our estimate for the energy barrier EB between these states obtained for the photodarkening process (EB∼0.8 eV) coincides with that obtained from the analysis of the relaxation process. At room temperature, an irreversible component of photodarkening has been observed along with the reversible one. The energy barrier responsible for the relaxation of the reversible component at room temperature appears the same as at 35 °C. This suggests that the energy barrier identified represents a fundamental feature of the photoinduced structural metastability in amorphous selenium. [ABSTRACT FROM AUTHOR]

Photoluminescence in (GaIn)(NAs) quantum wells designed for laser emission was studied experimentally and theoretically. The observed temperature dependences of the luminescence Stokes shift and of the spectral linewidth evidence the essential role of disorder in the dynamics of the recombining excitations. The spatial and energy disorders can cause a localization of photocreated excitations supposedly in the form of excitons. Theoretical study of the exciton dynamics is performed via kinetic Monte Carlo simulations of exciton hopping and recombination in the manifold of localized states. Direct comparison between experimental spectra and theoretical calculations provides quantitative information on the energy scale of the potential fluctuations in (GaIn)(NAs) quantum wells. The results enable one to quantify the impact of annealing on the concentration of localized states and/or on the localization length of excitons in (GaIn)(NAs) quantum wells. [ABSTRACT FROM AUTHOR]