Search

The long-term stability in acidic or alkaline aqueous electrolytes of p-Ga0.52In0.48P photocathodes, with a band gap of ∼1.8 eV, for the solar-driven hydrogen-evolution reaction (HER) has been evaluated from a thermodynamic, kinetic, and mechanistic perspective. At either pH 0 or pH 14, etched p-GaInP electrodes corroded cathodically under illumination and formed metallic In0 on the photoelectrode surface. In contrast, under the same conditions, electrodeposition of Pt facilitated the HER kinetics and stabilized p-GaInP/Pt photoelectrodes against such cathodic decomposition. When held at 0 V versus the reversible hydrogen electrode, p-GaInP/Pt electrodes in either pH = 0 or pH = 14 exhibited stable current densities (J) of ∼-9 mA cm-2 for hundreds of hours under simulated 1 sun illumination. During the stability tests, the current density-potential (J-E) characteristics of the p-GaInP/Pt photoelectrodes degraded due to pH-dependent changes in the surface chemistry of the photocathode. This work provides a fundamental understanding of the stability and corrosion mechanisms of p-GaInP photocathodes that constitute a promising top light absorber for tandem solar-fuel generators.

Computational studies are employed to construct our understanding of systems and to reduce the monetary and temporal demands of research and development. Proton exchange membrane water electrolysis (PEMWE) devices, with their intricate two-phase transport phenomena and numerous realizable applications, provide an excellent opportunity to utilize computational fluid dynamics (CFD). Toghyani et al.1 modeled the performance of a high-temperature, vapor-fed PEMWE device using CFD simulations, finding fair agreement with prior experimental studies. For low-temperature electrolysis, Nie and Chen2 used a mixture model to study the flow regimes in liquid-fed channels. We employed a CFD model to simulate a PEMWE device, exploring the viability of isothermal and non-isothermal mixture models for a liquid-fed cell. The flow rate was altered to study the change in cell temperature and performance, and the model results were compared to experimental data. Additionally, bulk properties of the porous transport layer at the anode were altered to examine performance effects; such effects were expected to be virtually non-existent in light of experimental observations.3,4 The results demonstrate when a continuum assumption is best utilized to predict electrolysis efficiency. References: S. Toghyani, E. Afshari, and E. Baniasadi, Journal of Thermal Analysis and Calorimetry, 135, 1911–1919 (2019). J. Nie and Y. Chen, International Journal of Hydrogen Energy, 35, 3183–3197 (2010). T. Schuler, T. J. Schmidt, and F. N. Büchi, Journal of The Electrochemical Society, 166, F555–F565 (2019). J. Lopata et al., Journal of The Electrochemical Society, 167, 064507 (2020). Figure 1

While photoelectrochemical (PEC) solar-to-hydrogen efficiencies have greatly improved over the past few decades, advances in PEC durability have lagged behind. Corrosion of semiconductor photoabsorbers in the aqueous conditions needed for water splitting is a major challenge that limits device stability. In addition, a precious-metal catalyst is often required to efficiently promote water splitting. Herein, we demonstrate unassisted water splitting using a nonprecious metal molybdenum disulfide nanomaterial catalytic protection layer paired with a GaInAsP/GaAs tandem device. This device was able to achieve stable unassisted water splitting for nearly 12 h, while a sibling sample with a PtRu catalyst was only stable for 2 h, highlighting the advantage of the nonprecious metal catalyst. In situ optical imaging illustrates the progression of macroscopic degradation that causes device failure. In addition, this work compares unassisted water splitting devices across the field in terms of the efficiency and stability, illustrating the need for improved stability.

Durable performance and high efficiency in solar-driven water splitting are great challenges not yet co-achieved in photoelectrochemical (PEC) cells. Although photovoltaic cells made from III–V semiconductors can achieve high optical–electrical conversion efficiency, their functional integration with electrocatalysts and operational lifetime remain great challenges. Herein, an ultra-thin TiN layer was used as a diffusion barrier on a buried junction n+p-GaInP2 photocathode, to enable elevated temperatures for subsequent catalyst growth of Ni5P4 as nano-islands without damaging the GaInP2 junction. The resulting PEC half-cell showed negligible absorption loss, with saturated photocurrent density and H2 evolution equivalent to the benchmark photocathode decorated with PtRu catalysts. High corrosion-resistant Ni5P4/TiN layers showed undiminished photocathode operation over 120 h, exceeding previous benchmarks. Etching to remove electrodeposited copper, an introduced contaminant, restored full performance, demonstrating operational ruggedness. The TiN layer expands the synthesis conditions and protects against corrosion for stable operation of III–V PEC devices, while the Ni5P4 catalyst replaces costly and scarce noble metal catalysts.

Monolithic perovskite/perovskite tandem solar cells have attracted substantial attention owing to their promise for high power conversion efficiency (PCE) and low fabrication cost. Conventional all-perovskite tandem solar cells employ a mixed tin (Sn)-lead (Pb) low-bandgap subcell, which suffers from instability issues in the ambient air. Here, we fabricate two-terminal perovskite/perovskite tandem solar cells consisting of two solution-processed perovskite subcells based on the more airstable pure Pb-based perovskites. The champion perovskite tandem cell exhibits a PCE of 19.2% with a high open-circuit voltage of 2.15 V. We further demonstrate photovoltaicelectrolysis (PV-EC) water-splitting applications using these high-photovoltage all-perovskite tandem solar cells.

The research and development of proton exchange membrane water electrolysis (PEMWE) is an upcoming and growing area due to a rising interest in hydrogen as an energy carrier. Operating conditions are harsher than in a fuel cell system, particularly because the potentials required for the oxygen evolution reaction are significantly higher. In commercial water electrolysis systems, this is compensated by typically using titanium material sets that are often protected against oxidation through coating processes. Such material choices make small scale research hardware and porous transport layers expensive and difficult to source. In this work, we show that the stability of traditional, carbon-based fuel cell materials such as porous transport layers and graphite flow fields can be sufficient for electrolyzer initial performance characterization procedures such as cell conditioning, a limited number of polarization curve measurements, and electrochemical impedance spectroscopy. We identify and quantify the onset of carbon degradation in porous transport layers with regards to operating length and define a strategy that enables the utilization of standard fuel cell hardware for short-term PEMWE experiments. With the knowledge that existing fuel cell material sets can be applied to conduct electrolyzer research when adhering to such limitations, fuel cell research hardware and experience can be more readily transferred to the younger and rapidly growing electrolysis research field.

The production of hydrogen fuels, via water splitting, is of practical relevance for meeting global energy needs and mitigating the environmental consequences of fossil-fuel-based transportation. Water photoelectrolysis has been proposed as a viable approach for generating hydrogen, provided that stable and inexpensive photocatalysts with conversion efficiencies over 10% can be discovered, synthesized at scale, and successfully deployed (Pinaud et al., Energy Environ. Sci., 2013, 6, 1983). While a number of first-principles studies have focused on the data-driven discovery of photocatalysts, in the absence of systematic experimental validation, the success rate of these predictions may be limited. We address this problem by developing a screening procedure with co-validation between experiment and theory to expedite the synthesis, characterization, and testing of the computationally predicted, most desirable materials. Starting with 70 150 compounds in the Materials Project database, the proposed protocol yielded 71 candidate photocatalysts, 11 of which were synthesized as single-phase materials. Experiments confirmed hydrogen generation and favorable band alignment for 6 of the 11 compounds, with the most promising ones belonging to the families of alkali and alkaline-earth indates and orthoplumbates. This study shows the accuracy of a nonempirical, Hubbard-corrected density-functional theory method to predict band gaps and band offsets at a fraction of the computational cost of hybrid functionals, and outlines an effective strategy to identify photocatalysts for solar hydrogen generation.

Gallium indium phosphide (GaInP2) is a semiconductor with promising optical and electronic properties to serve as the large bandgap, top junction in a dual absorber tandem solar water splitting device. Poor intrinsic catalytic ability and surface corrosion in aqueous electrolyte remain key obstacles. Significant progress has been made developing thin-film protection layers and active catalysts for photoelectrochemical devices, but combining these into a catalytic protection layer that can provide long-term stability without sacrificing performance has proven difficult due, in large part, to challenges in developing active and stable interfaces. In this work, we demonstrate that a nanoscale molybdenum disulfide (MoS2) film functions both as an effective protection layer and excellent hydrogen evolution catalyst for GaInP2 photocathodes, with only a ∼10% loss in initial light-limited current density after 100 h, and a photocurrent onset potential better than that of the same state-of-the-art device with a platinum–ruthenium catalyst. Using transient photoreflectance spectroscopy, we probed the carrier dynamics of these photocathodes and show that the MoS2 coated device exhibits improved electron transfer at the surface interface compared to the PtRu catalyzed device. These MoS2 protected devices are among the most active and stable single-absorber photocathodes for solar water splitting to date and offer a promising pathway towards generating hydrogen with high efficiency and significant longevity.

Starting from the classical GaInP/GaAs tandem photoelectrochemical water splitting device, higher solar-to-hydrogen efficiencies can be pursued by extending photon absorption to longer wavelengths. We incorporate strain-balanced GaInAs/GaAsP quantum wells into the bottom GaAs junction, to increase the range of photon absorption. The inclusion of 1.34 eV quantum wells in the depletion region of the bottom cell extends the absorption edge to 930 nm. With a corresponding increase in the thickness of the top cell for current matching, the light-limiting photocurrent increases by >8%. The estimated solar-to-hydrogen efficiency is 13.6 ± 0.5%, and we show a pathway to further improvement. With the semiconductor device remaining on the growth substrate, this quantum well architecture may enable improved stability and durability of the photoelectrochemical electrodes.

While III-V semiconductors have achieved the highest photo-electrochemical solar-to-hydrogen conversion efficiencies, they are remarkably unstable during operation in a harsh electrolyte. The first part of this talk will focus on the degradation mechanism of inverted metamorphic mulijunction (IMM) III-V cells and surface modification strategies aimed at protecting them from photocorrosion. We applied noble metal catalysts, oxide coatings by atomic layer deposition, and MoS2 in an effort to protect the GaInP2 surface that was in contact with acidic electrolyte. We also grew epitaxial capping layers from III-V alloys that should be more intrinsically stable than GaInP2. The ability of the various modifications to protect the IMM’s surface was evaluated by operating at each electrode at short circuit for extended periods of time. The second part of this talk will identify the challenges encountered while scaling the IMM III-V absorber areas of from ~0.15 cm2 up to 16 cm2 and incorporating them in a photoreactor capable of generating 3 standard liters of hydrogen in 8 hours under natural sunlight. To successfully scale photo-electrochemical water-splitting technologies from bench to demonstration size requires addressing predictable and unpredictable complications. Despite using Comsol multiphysics to model our photoreactor and identify suitable specifications for a prototype, several practical issues were uncovered during testing that led to multiple iterations of photoreactor design between the initial and final generations. Several bottlenecks that ranged from counter electrode composition and orientation to bubble management needed redress in order to meet our performance targets. Ultimately, the demonstration-scale system was able to generate nearly twice the target volume of hydrogen in an 8-hour outdoor trial.

Expanding upon our prior experimental work, we constructed a three-dimensional model of a polymer electrolyte membrane water electrolyzer using computational fluid dynamics. We applied the assumption of pseudo-two-phase flow, the flow of two phases with equal velocity. Experimental data were used to obtain parameters and to determine the conditions under which this model was valid. Anodic distributions of current density, temperature, liquid saturation, and relative humidity were obtained at various flow rates. The overall current density and temperature difference from inlet to outlet at the anode agreed strongly with experimental measurements under most circumstances. This verification allowed us to further examine the apparent gas coverage calculated from experimental and model temperature data. Results suggested a low liquid saturation and low relative humidity at the anode due to the consumption of liquid water and water vapor. However, we questioned the accuracy of the pseudo-two-phase assumption at low water feed rates. We concluded that the model was applicable to systems with liquid water feed rates greater than 0.6 ml min−1 cm−2. Therefore, it is a fair screening method that can advise which operating conditions lead to excessive temperatures or drying at the anode, thereby promoting the longevity of the membrane and catalyst.

Earth−abundant Copper-Barium-Thiostannate Cu2BaSnS4 (CBTS)-based thin films have recently been reported to exhibit the optoelectronic and defect properties suitable as absorbers for photoelectrochemical (PEC) water splitting and the top cell of tandem photovoltaic solar cells. However, the photocurrents of CBTS-based PEC devices are still much lower than the theoretical value, partially due to ineffective charge collection at CBTS/water interface and instability of CBTS in electrolytes. Here, we report on overcoming these issues by employing overlayer engineering. We find that CdS/ZnO/TiO2 overlayers can significant-ly improve the PEC performance, achieving saturated cathodic photocurrents up to 7.8 mA cm−2 at the potential of -0.10 V versus reversible hydrogen electrode (RHE) in a neutral electrolyte solution, which is much higher than the best bare CBTS film attaining a photocurrent of 4.8 mA cm−2 at the potential of -0.2 V versus RHE. Our results suggest a viable approach for improving the performance ...

Gallium indium phosphide (GaInP2) is a semiconductor with a nearly ideal bandgap for solar water-splitting as the top absorber in a dual junction tandem absorber device. It has been used in conjunction with a gallium arsenide (GaAs) bottom absorber in an overall water splitting cell with 12.4% solar-to-hydrogen (STH) efficiency, one of the highest STH efficiencies for an integrated photoelectrochemical (PEC) water-splitting device reported to date. However, GaInP2 suffers from one of the biggest challenges facing the field: instability due to electrochemical corrosion in aqueous electrolytes. Molybdenum disulfide (MoS2) nanomaterials can be used to both protect GaInP2 and significantly improve its catalytic ability since it is resistant to corrosion and also possesses high activity for the hydrogen evolution reaction (HER). In this work, we demonstrate that GaInP2 photocathodes coated with thin MoS2 surface protecting layers exhibit excellent activity and stability for solar hydrogen production and we probe the details of failure mechanisms using novel flow cell microscopic and spectroscopic techniques. Our GaInP2 photocathodes demonstrated no loss in performance (photocurrent onset potential, fill factor, and light limited current density) until 60 hours of operation which represents a five-hundred fold increase in stability compared to bare p-GaInP2 samples tested in identical conditions. We believe this to be one of the first successful attempts to stabilize GaInP2 using a thin film protection layer scheme. Furthermore, as this protection scheme has previously been used successfully on silicon photocathodes, this work highlights the potential for MoS2 to be used as a thin film protection layer for many different semiconductor water splitting devices that are unstable in acid. Using a custom-designed flow cell coupled with various microscopic and spectroscopic techniques (optical, Raman, FT-IR), we gained a greater understanding of the failure mechanisms of MoS2 as a thin-film protection layer. We discovered that pinhole formation in the MoS2 layer exposes the GaInP2 substrate, which readily corrodes in the acidic conditions, ultimately leading to device degradation. The flow cell further allowed us to capture the time scale of this pinhole formation. These insights represent a deeper understanding of MoS2 as a protection layer and can be leveraged to improve the stability of thin film protected semiconductor water splitting devices. References Khaselev, O.; Turner, J. A., A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production Via Water Splitting. Science 1998, 280, 425-427. Benck, J. D.; Lee, S. C.; Fong, K. D.; Kibsgaard, J.; Sinclair, R.; Jaramillo, T. F., Designing Active and Stable Silicon Photocathodes for Solar Hydrogen Production Using Molybdenum Sulfide Nanomaterials. Advanced Energy Materials 2014, 4, 1-8 Britto R.J., Benck J.D., Young J.L., Hahn C., Deutsch, T.G., Jaramillo T.F. In Review (2016) Figure 1

CuGa3Se5 is a promising candidate material with wide band gap for top cells in tandem photovoltaic and photoelectrochemical (PEC) devices. However, traditional CdS contact layers used with other chalcopyrite absorbers are not suitable for CuGa3Se5 due to the higher position of its conduction band (CB) minimum. Mg x Zn1− x O (MZO) is a transparent oxide with adjustable band gap and CB position as a function of magnesium composition, but its direct application is hindered by CuGa3Se5 surface oxidation. Here, MZO is investigated as a contact (n-type ‘buffer’ or ‘window’) material to CuGa3Se5 absorbers pretreated in Cd2+ solution, and an onset potential close to 1 V vs reversible hydrogen electrode in 10 mM hexaammineruthenium (III) chloride electrolyte is demonstrated. The Cd2+ surface treatment changes the chemical composition and electronic structure of the CuGa3Se5 surface, as demonstrated by photoelectron spectroscopy measurements. The performance of CuGa3Se5 absorber with Cd2+ treated surface in the solid-state test structure depends on the Zn/Mg ratio in the MZO layer. The measured open circuit voltage of 925 mV is promising for tandem PEC water splitting with CuGa3Se5/MZO top cells.

Catalytic interface of semiconductor photoelectrodes is critical for high-performance photoelectrochemical solar water splitting because of its multiple roles in light absorption, electrocatalysis, and corrosion protection. Nevertheless, simultaneously optimizing each of these processes represents a materials conundrum owing to conflicting requirements of materials attributes at the electrode surface. Here we show an approach that can circumvent these challenges by collaboratively exploiting corrosion-resistant surface stoichiometry and structurally-tailored reactive interface. Nanoporous, density-graded surface of ‘black’ gallium indium phosphide (GaInP2), when combined with ammonium-sulfide-based surface passivation, effectively reduces reflection and surface recombination of photogenerated carriers for high efficiency photocatalysis in the hydrogen evolution half-reaction, but also augments electrochemical durability with lifetime over 124 h via strongly suppressed kinetics of corrosion. Such synergistic control of stoichiometry and structure at the reactive interface provides a practical pathway to concurrently enhance efficiency and durability of semiconductor photoelectrodes without solely relying on the development of new protective materials., Photoelectrochemical water splitting presents an integrated means storing sunlight into fuels, yet high optical losses and corrosion limit device performance. Here, authors boost absorption and durability in gallium-indium phosphide photocathodes via a sulfurized and nanostructured protection layer.

The photoluminescence (PL) intensity of semiconductors can be modulated by their ambient. We show GaInP2 to respond reversibly to water vapor, irreversibly to oxygen, and with a time dependence to air. We characterize the reversible PL response to water vapor in a set of steady-state measurements that reveal a systematic dependence on pressure. We derive a model for this behavior based on Langmuir adsorption and Shockley–Read–Hall recombination principles to describe how partial pressure controls luminescence. The expression for the GaInP2/water vapor system shows excellent agreement to measurements. Combined, the PL monitoring technique and model demonstrate a quantitative approach for probing gas/surface defect interactions of semiconductor processing steps, luminescence-based sensors, and photocatalytic surfaces.

Illumination characteristics from artificial sources strongly influence the experimental performance of solar water-splitting devices, with the highest impact on tandem structures designed for optimum conversion efficiency. We highlight quantitative and qualitative flaws of common characterization techniques, discuss their impact on research results and strategy, and demonstrate approaches toward advanced measurement accuracy.

Solar photoconversion in semiconductors is driven by charge separation at the interface of the semiconductor and contacting layers. Here we demonstrate that time-resolved photoinduced reflectance from a semiconductor captures interfacial carrier dynamics. We applied this transient photoreflectance method to study charge transfer at p-type gallium-indium phosphide (p-GaInP2) interfaces critically important to solar-driven water splitting. We monitored the formation and decay of transient electric fields that form upon photoexcitation within bare p-GaInP2, p-GaInP2/platinum (Pt), and p-GaInP2/amorphous titania (TiO2) interfaces. The data show that a field at both the p-GaInP2/Pt and p-GaInP2/TiO2 interfaces drives charge separation. Additionally, the charge recombination rate at the p-GaInP2/TiO2 interface is greatly reduced owing to its p-n nature, compared with the Schottky nature of the p-GaInP2/Pt interface.

The p-type semiconductor GaInP2 has a nearly ideal bandgap (∼1.83 eV) for hydrogen fuel generation by photoelectrochemical water splitting but is unable to drive this reaction because of misalignment of the semiconductor band edges with the water redox half reactions. Here, we show that attachment of an appropriate conjugated phosphonic acid to the GaInP2 electrode surface improves the band edge alignment, closer to the desired overlap with the water redox potentials. We demonstrate that this surface modification approach is able to adjust the energetic position of the band edges by as much as 0.8 eV, showing that it may be possible to engineer the energetics at the semiconductor/electrolyte interface to allow for unbiased water splitting with a single photoelectrode having a bandgap of less than 2 eV.

Our goal is to improve solar-to-hydrogen (STH) efficiency from just over 10% to over 20% via novel tandem semiconductor materials and configurations. Our primary focus is to develop inverted metamorphic multijunction (IMM) III-V semiconductors that have bandgaps optimized for water splitting. We will also discuss measurement challenges in appraising STH efficiency, some of which are specific to tandem absorbers. Using more stringent measurement standards, we have confirmed 16.2% STH on our most advanced IMM devices.

Solar water splitting via multi-junction semiconductor photoelectrochemical cells provides direct conversion of solar energy to stored chemical energy as hydrogen bonds. Economical hydrogen production demands high conversion efficiency to reduce balance-of-systems costs. For sufficient photovoltage, water-splitting efficiency is proportional to the device photocurrent, which can be tuned by judicious selection and integration of optimal semiconductor bandgaps. Here, we demonstrate highly efficient, immersed water-splitting electrodes enabled by inverted metamorphic epitaxy and a transparent graded buffer that allows the bandgap of each junction to be independently varied. Voltage losses at the electrolyte interface are reduced by 0.55 V over traditional, uniformly p-doped photocathodes by using a buried p–n junction. Advanced on-sun benchmarking, spectrally corrected and validated with incident photon-to-current efficiency, yields over 16% solar-to-hydrogen efficiency with GaInP/GaInAs tandem absorbers, representing a 60% improvement over the classical, high-efficiency tandem III–V device. Solar water-splitting efficiency can be enhanced by careful bandgap selection in multi-junction semiconductor structures. Young et al. demonstrate a route that allows independent bandgap tuning of each junction in an immersed water-splitting device, enabling a solar-to-hydrogen efficiency of over 16%.

The present disclosure relates to a composition that includes, in order: a first layer that includes MAw; a second layer that includes MOyAz; and a third layer that includes MOx, where M includes a transition metal, A includes at least one of sulfur, selenium, and/or tellurium, w is between greater than zero and less than or equal to five, x is between greater than zero and less than or equal to five, y is between greater than zero and less than or equal to five, and z is between greater than zero and less than or equal to five. In some embodiments of the present disclosure, the transition metal may include at least one of molybdenum and/or tungsten. In some embodiments of the present disclosure, A may be sulfur.

SummaryResearch during the last two decades established atheromatous lesions as active sites of inflammation and immune responses, contrasting to the traditional view of atherosclerosis as an acellular lesion composed of lipid deposits. In particular, cytokines appear to orchestrate the chronic development of atherosclerosis, eventually leading to the formation of complex atherosclerotic plaques, which can trigger acute thromboembolic complications, such as myocardial infarction or stroke. Indeed the rupture-prone plaque, characterized by a thin fibrous cap overlaying a voluminous lipid core, exhibits accumulation of various pro-inflammatory cytokines. These cytokines may control the clinical consequences of plaques by mediating infiltration and accumulation of immunocompetent cells, directing the turnover of fibrillar collagens (governing the fragility of the fibrous cap), or enhancing foam cell formation and thrombogenicity of the lipid core, among other processes outlined in this review. Thus, understanding the role of cytokines in the pathophysiology of the atherosclerotic plaque might provide a promising therapeutic avenue for this prevalent human disease. This review will focus on members of the interleukin, tumor necrosis factor, and interferon families of cytokines in modulating key processes of atherogenesis.

This chapter introduces and describes the process of medical evaluation, also termed medical screening, of the psychiatric patient in the emergency department (ED). It discusses the diagnosis of medical mimics, along with the utility of both the patient history and physical exam and laboratory evaluations. The evaluation that an emergency physician conducts is an extremely important and, albeit, limited chance for the patient to be treated for a medical condition that may be causing their symptoms. The chapter also discusses the use of standard screening algorithms, which have been shown in several studies to decrease testing costs for ED patients undergoing medical screening. Local processes, such as coordination of care, trust between providers, wait times for subsequent psychiatric admission, facility overcrowding, and subgroup demographics may play a strong role in acceptance and accuracy of the emergency medicine evaluation process.

Urinary macromolecular uronate and glycosaminoglycan uronate concentrations were determined in 209 urine specimens obtained from 192 interstitial cystitis patients, 47 asymptomatic normal individuals and 32 spinal cord injury patients. As a group the concentration of macromolecular uronate or glycosaminoglycan uronate was significantly less in the interstitial cystitis patients than in the normal controls. Some interstitial cystitis patients showed low values of macromolecular uronate and glycosaminoglycan uronate. Analysis of the population distributions suggested that macromolecular uronate may have significant value in diagnosis of interstitial cystitis.

When patients present to the emergency department with changes in behavior and levels of consciousness, psychiatric causes often move to the top of the list of diagnostic considerations. It is important to thoroughly assess such patients for medical causes. Although it is not common for primary psychiatric conditions to present with altered levels of consciousness, severe cases may present in this fashion. Altered mental states may also be caused by adverse reactions to psychiatric medications. In this article, the authors review some of the psychiatric causes of decreased levels of consciousness, as well as certain adverse drug reactions to psychotropic medications.

Omnivore is a single cylinder spark ignition based research engine conceived to maximize the operating range of auto-ignition on a variety of fossil and renewable fuels. In order to maximize auto-ignition operation, the two-stroke cycle was adopted with two independent mechanisms for control. The charge trapping valve system is incorporated as a means of varying the quantity of trapped residuals whilst a variable compression ratio mechanism is included to give independent control over the end of compression temperature. The inclusion of these two technologies allows the benefits of trapped residual gas to be maximised (to minimize NOx formation) whilst permitting variation of the onset of auto-ignition. 2000rpm and idle are the main focus of concern whilst also observing the influence of injector location. This paper describes the rational behind the engine concept and presents the results achieved at the time of writing using 98ulg and E85 fuels. Copyright

In this talk I will present an overview of our research strategy to develop a semiconductor-based device capable of over 20% solar-to-hydrogen efficiency with several thousand hours of stability under operating conditions. Our goal is to improve solar-to-hydrogen (STH) efficiency from 12.4% to over 20% by developing novel tandem semiconductor materials and configurations. Our approach focuses on classes of materials that have either demonstrated exceptionally high efficiency or theoretically can produce highly efficient materials. The four tandem material sets in our research portfolio are III-Vs on GaAs, InGaN on Si, III-V-N on Si, and dual photoelectrode pairings. We are evaluating catalytic nitride, oxide, and sulfide-based semiconductor surface modifications to extend durability from a few hundred hours to nearly 1000 hours, with a stretch target of 3500 hours. Cost reductions in the synthesis of high-efficiency III-V photoelectrochemical devices could be realized from emerging epitaxial synthesis technologies such as spalling, epitaxial lift-off, close-space vapor transport, or hydride vapor phase epitaxy to yield economical hydrogen production. Our group addresses synthesis cost, in a limited capacity, by investigating novel material configurations. Within the next few years, we plan to demonstrate a prototype photoreactor that produces 3 L of standard hydrogen within an 8-hour period under moderate solar concentration (10x), which can be accomplished using only 6 cm2 of a 20% STH material.

Allopurinol, introduced in 1963, 1 has proved to be a useful agent for the treatment of gout and hyperuricemia. 2-7 Although serious toxicity has been unusual, recent case reports of agranulocytosis, 8 granulomatous hepatitis, 9 and exfoliative dermatitis 10 have appeared. In addition, four cases have been reported of severe, prolonged hypersensitivity reactions characterized by an erythematous maculopapular eruption, eosinophilia, fever, abnormal results of liver-function tests, and rapidly progressive renal failure. 11-13 The purpose of this communication is to describe two further cases of apparent hypersensitivity vasculitis and to explore possible predisposing factors. Patient Summaries Patient 1. —A 40-year-old black man was admitted to Vanderbilt University Hospital on April 14,1971, with a chief complaint of skin rash and fever. The patient's course had been followed at Vanderbilt since 1953 for psychomotor seizures, controlled with diphenylhydantoin sodium and phenobarbital. In 1963, during an evaluation for hypertension (blood pressure, 180/110 mm Hg)

Twenty-six patients were selected for treatment with minoxidil on the basis of hypertension which could not be controlled either because of (1) drug failures and/or (2) side effects of drugs. Sixteen out of the 26 had had one or more previous episodes of malignant hypertension. Reduced renal function was present in the majority; eight patients were on dialysis. Average preminoxidil blood pressure was 202/127 mm. Hg supine and 162/106 upright which fell to 154/87 supine and 143/86 upright after minoxidil. Propranolol or methyldopa was given to control the reflex increase in heart rate. Edema and congestive heart failure refractory to large doses of potent diuretics necessitated discontinuation of the drug in two patients. Minoxidil proved highly efficacious regardless of initial level of blood pressure, etiology, or supine or upright posture.

Propranolol could not be detected in samples of plasma and left atrium obtained from eight patients during coronary bypass surgery 36 to 48 hours after withdrawal from chronic therapy. The norepinephrine sensitivity of strips of left atria obtained from four similar patients was not different from that in six control patients who had not previously received propranolol. In three ambulant patients, serial estimates of the chronotropic and inotropic responses to isoproterenol were made at daily intervals during withdrawal from propranolol. Isoproterenol sensitivity became stable or returned to control levels within 48 hours. These findings were confirmed by experiments in the rat. A withdrawal time of 48 hours thus appears sufficient for complete recovery from the cardiac effects of propranolol and any possibly active metabolites, and coronary bypass surgery should present no additional hazard. (N Engl J Med 289:607–609, 1973)

A description is given of a mobile laboratory equipped with two spectrographs for radiance measurements of the sky and terrain between 1 and 20 μ. The laboratory has its own ac power supply and means for controlling its temperature. Procedures are described for calibrating the instrumentation and transforming the data into spectral radiance (in microwatts cm−2 steradian−1 micron−1) as a function of wavelength.

Quantitative data are presented to illustrate the infrared spectral radiance of the sky under a variety of situations. A qualitative discussion of the dominant spectral features is given to show the importance of the emission and scattering processes, the effect of angle of elevation, angle of azimuth, sun angle, and cloud cover.

A mobile infrared spectrographic laboratory has been used to make absolute determinations of the apparent infrared spectral radiance of various types of terrain. The spectral distribution of the observed radiation indicates the predominance of reflected sun and sky radiation at wavelengths less than approximately 3 μ, and thermal emission at longer wavelengths. Examples are shown for a number of types of terrain observed in various locations and conditions. The transition between the sky and the ground is also illustrated by spectra taken near the horizon. The spectra of gypsum and silica sands show reststrahlen effects in the atmospheric window of wavelengths between 8 and 13 μ. Many of the features of the spectra of terrain can be explained, in some cases quantitatively, on the basis of known parameters of the particular background and its atmospheric environment.