Integrated photovoltaic-thermal solar energy conversion systems

A combined photovoltaic/thermal collector has been built and is now being tested. Initial tests have concentrated on evaluating the thermal efficiency of the collector before and after the silicon cells are mounted. With likely improvements in bonding between cells and receiver and in the absorptivity of the cells, thermal efficiencies greater than 50% can be expected for the combined receiver operating at 100 C

Cirugía funcional en cadera con mielomeningocele: osteotomía extensora subtrocantérica con tutor externo: presentación de técnica

En pacientes con miclomeningoccle la deformidad en flexión de cadera es uno de los factores que afectan adversamente el pronóstico de marcha. En niveles altos (torácicos y lumbares altos) la contracture en flexión dificulta el equipamiento; en niveles mas bajos (lumbares bajos) produce una inclinación anterior de la pelvis y lordosis, que aumentan los requerimientos de los miembros superiores durante la bipedestación y marcha, y dolor lumbar a mayor edad. En caso de existir una contracture en flexión de cadera unilateral o asimétrica puede predisponer a una oblicuidad pélvica, con las consecuencias que ésta produce en la alineación de columna y miembros inferiores. Se presentan los resultados preliminares de la osteotomía subtrocantérica extensora de cadera fijada con tutor externo TIM (tutor infantil multidirectional) en pacientes con diagnóstico de mielomeningocele. Se operaron 14 caderas en 8 pacientes con deformidades en flexión de 34,64° (20 a 60°). Se midió la extensión de cadera, el ángulo femorosacro y la lordosis pre y postoperatorias. La extensión postoperatoria fue de 0° en todos los casos; de los 6 pacientes con hiperlordosis preoperatoria (87,5°) se obtuvieron correcciones entre 5 y 18° (75,5° postoperatoria); el ángulo femorosacro y preoperatorio fue de -30,4° (-12 a -45°) y el postoperatorio de 8° (0 a 10°). La tolerancia al tutor fue buena, obteniéndose la consolidación en 85 días (63 a 87 días), a excepción de 1 caso en el que hubo aflojamiento de uno de los tutores y pérdida de alineación, que fue corregida retirando el tutor y colocando yeso pelvipédico.Hip flexion deformity is an adverse prognostic factor for the evolution of gait in patients with myelomeningocele. In high level lesions (thoracic and upper lumbar), it prevents proper orthotic use. In low level lesions (lower lumbar), hip flexion deformity produces anterior pelvic tilt and hyperlordosis with foward flexion during gait, a eventually low back pain. A series of 14 hips in 8 patients were operated. Hip flexion deformity (Thomas lest): mean 34° (from 20° to 60°). Femorosacral angle (Bleck): mean -30° (from -12° to -45°). Lumbar lordosis (Cobb): mean 87°. The fixator is placed using 4 pins, with the fixatior joints al 0°, a percutaneous osteotomy is performed, complete correction is done at the time of surgery, angulating the fixator's A-P joint, then the fixator's joints are fixed. Consolidation occured at (mean) 85 days (from 63 to 87). Follow up: mean 14 months (from 4 to 48). Hip flexion deformity: pre-surgery 34°; post-surgery 8°. Lumbar lordosis: pre-surgery 87°; post-surgery 75°. Minor complications occured such as pin tract infection and one case of pin loosening. Hip extension subtrocanteric osteotomy corrects the deformity without damage of useful hip flexors. The advantages of external fixation vs internal fixation are: minimal surgical invasion, inmediate weight bearing (avoids post-inmovilization osteoporosis). Allows corrections post-surgery if needed, no need of second surgical procedure under general anesthesia for hardware removal

Drastic method to map groundwater vulnerability to pollution using nitrate measurements in agricultural areas

Η μέθοδος DRASTIC χρησιμοποιείται για την εκτίμηση και τη χαρτογράφηση της εσωτερικής τρωτότητας των υπόγειων νερών από εξωτερικά ρυπαντικά φορτία. Δεδομένου όμως, ότι η μέθοδος εφαρμόζεται σε διαφορετικές περιοχές, χωρίς καμία τροποποίηση, την καθιστά αδύνατη να λάβει υπόψη της τις επιδράσεις του ρυπαντή, ανάλογα με το είδος και τα χαρακτηριστικά του. Συνεπώς, στη μέθοδο DRASTIC θα πρέπει να συνυπολογίζονται τόσο οι ιδιαίτεροι παράμετροι του φυσικού συστήματος του υδροφορέα, όσο και οι ιδιαίτερες συνθήκες κάθε περιοχές (χρήσεις γης). Στα πλαίσια της παρούσας εργασίας, τροποποιώντας τις παραμέτρους της τυπικής μεθόδου DRASTIC και τους αντίστοιχους συντελεστές βαρύτητας, εκτιμήθηκε ο δείκτης τρωτότητας με μεγαλύτερη ακρίβεια. Την περιοχή εφαρμογής της προτεινόμενης μεθοδολογίας αποτελεί η Δελταϊκή περιοχή του προσχωματικού υδροφόρου ορίζοντα του ποταμού Βολιναίου, στην ΒΔ/κή Πελοπόννησο.DRASTIC model has been used to map groundwater vulnerability to pollution in many areas. Since this method is used in different places without any changes, it cannot consider the effects of pollution type and characteristics. Therefore, the method needs to be calibrated and corrected for that aquifer and specific land use. In this research, by correcting the rates of DRASTIC parameters, one can assess the vulnerability potential to pollution more accurately. The new rates were computed using the relationships between DRASTIC INDEX (DI) corresponding to land use and to nitrate concentration in groundwater. The proposed methodology was applied in deltaic region of alluvial aquifer of Volinaios catchment located in the northwestern part of Peloponnesus. In order to determine the quality of the ground waters, either for watering or irrigating purposes, in the study area, a sampling was made. Correlation was used to find the relationship between the index and measured pollution in each point and therefore, to modify the rates. The results showed that the modified DRASTIC is better than the original method for nonpoint source pollution in agricultural areas

On the Persistent Shape and Coherence of Pulsating Auroral Patches

The pulsating aurora covers a broad range of fluctuating shapes that are poorly characterized. The purpose of this paper is therefore to provide objective and quantitative measures of the extent to which pulsating auroral patches maintain their shape, drift and fluctuate in a coherent fashion. We present results from a careful analysis of pulsating auroral patches using all-sky cameras. We have identified four well-defined individual patches that we follow in the patch frame of reference. In this way we avoid the space-time ambiguity which complicates rocket and satellite measurements. We find that the shape of the patches is remarkably persistent with 85-100% of the patch being repeated for 4.5-8.5 min. Each of the three largest patches has a temporal correlation with a negative dependence on distance, and thus does not fluctuate in a coherent fashion. A time-delayed response within the patches indicates that the so-called streaming mode might explain the incoherency. The patches appear to drift differently from the SuperDARN-determined $\stackrel{\rightarrow}{E}$ X $\stackrel{\rightarrow}{B}$ convection velocity. However, in a nonrotating reference frame the patches drift with 230-287 m/s in a north eastward direction, which is what typically could be expected for the convection return flow

Tailorable, visible light emission from silicon nanocrystals

J. P. Wilcoxon and G. A. Samara Crystalline, size-selected Si nanocrystals in the size range 1.8-10 nm grown in inverse micellar cages exhibit highly structured optical absorption and photoluminescence (PL) across the visible range of the spectrum. The most intense PL for the smallest nanocrystals produced This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. to induce a useful level of visible photoluminescence (PL) from silicon (Si). The approaches understood. Visible PL has been observed from Si nanocrystals, or quantum dots, produced by a variety of techniques including aerosols,2 colloids,3 and ion implantation.4 However, all of The optical absorption spectra of our nanocrystals are much richer in spectral features spectrum of bulk Si where the spectral features reflect the details of the band structure shown in nanocrystals estimated to have a Si core diameter of 1-2 nm. These measured quantum those in the spectrum of bulk Si in Fig. 1 are striking indicating that nanocrystals of this size 8-Room temperature PL results on an HPLC size-selected, purified 2 nm nanocrystals but blue shifted by -0.4 eV due to quantum confinement. Excitation at 245 nm yields the PL shows the PL spectrum for a similar sample excited at 490 nm (2.53 eV) trapped excitons at the surface of Si nanocrystals. The excitons are obtained for dimer bonds 1.8- 10 nm. These nanocrystals retain bulk-like optical absorption and an indirect bandgap Figure 1. The absorption spectrum of d = 2 nm Si nanocrystals compared to that of bulk7 Si. Figure 2. The extinction and PL (excitation at 490 nm) spectra ford= 8-10 nm Si nanocrystals

Evaluation of on-board hydrogen storage methods for hypersonic vehicles

Hydrogen is the foremost candidate as a fuel for use in high speed transport. Since any aircraft moving at hypersonic speeds must have a very slender body, means of decreasing the storage volume requirements below that for liquid hydrogen are needed. The total performance of the hypersonic plane needs to be considered for the evaluation of candidate fuel and storage systems. To accomplish this, a simple model for the performance of a hypersonic plane is presented. To allow for the use of different engines and fuels during different phases of flight, the total trajectory is divided into three phases: subsonic-supersonic, hypersonic and rocket propulsion phase. The fuel fraction for the first phase is found be a simple energy balance using an average thrust to drag ratio for this phase. The hypersonic flight phase is investigated in more detail by taking small altitude increments. This approach allowed the use of flight profiles other than the constant dynamic pressure flight. The effect of fuel volume on drag, structural mass and tankage mass was introduced through simplified equations involving the characteristic dimension of the plane. The propellant requirement for the last phase is found by employing the basic rocket equations. The candidate fuel systems such as the cryogenic fuel combinations and solid and liquid endothermic hydrogen generators are first screened thermodynamically with respect to their energy densities and cooling capacities and then evaluated using the above model

Random local strain effects in homovalent-substituted relaxor ferroelectrics: a first-principles study of BaTi0.74Zr0.26O3

We present first-principles supercell calculations on BaTi0.74Zr0.26O3, a prototype material for relaxors with a homovalent substitution. From a statistical analysis of relaxed structures, we give evidence for four types of Ti-atom polar displacements: along the , , or directions of the cubic unit cell, or almost cancelled. The type of a Ti displacement is entirely determined by the Ti/Zr distribution in the adjacent unit cells. The underlying mechanism involves local strain effects that ensue from the difference in size between the Ti4+ and Zr4+ cations. These results shed light on the structural mechanisms that lead to disordered Ti displacements in BaTi(1-x)Zr(x)O3 relaxors, and probably in other BaTiO3-based relaxors with homovalent substitution.Comment: 5 pages, 4 figure

Results of the post flash-flood disaster investigations in the Transylvanian Depression (Romania) during the last decade (2001–2010)

Flash-flood disasters are very rare in the Transylvanian Depression. In the last decades just three events were signalled in the study area, all of them during the last 10 years. The flash floods occurring in the study area during the last decade had a significant impact on several localities situated at the Transylvanian Depression border. Based on the post flash-flood investigation, the present study intends to find out the main characteristics of the flash floods and the causes that have led to disasters in a region rarely affected by such kinds of events. Analyzing the hydrological data, it has been seen that the maximum intensity of the flash floods was observed in the upper and middle basins. By comparing the unit peak discharges from the studied region with other specific peak discharges related to the significant flash floods from Romania, it was noticed that the events from the Transylvanian Depression have moderate to low intensity. On the other hand, the results showed that besides high stream power and unexpected character common to flash floods, the inappropriate flood risk management measures increased the dimension of the negative effects, leading to tens of lives lost and economical damages of tens of millions of dollars

A combined theoretical and experimental study of the low temperature properties of BaZrO3

Low temperature properties of BaZrO3 are revealed by combining experimental techniques (X-ray diffraction, neutron scattering and dielectric measurements) with theoretical first-principles-based methods (total energy and linear response calculations within density functional theory, and effective Hamiltonian approaches incorporating/neglecting zero-point phonon vibrations). Unlike most of the perovskite systems, BaZrO3 does not undergo any (long-range-order) structural phase transition and thus remains cubic and paraelectric down to 2 K, even when neglecting zero-point phonon vibrations. On the other hand, these latter pure quantum effects lead to a negligible thermal dependency of the cubic lattice parameter below ~ 40 K. They also affect the dielectricity of BaZrO3 by inducing an overall saturation of the real part of the dielectric response, for temperatures below ~ 40 K. Two fine structures in the real part, as well as in the imaginary part, of dielectric response are further observed around 50-65 K and 15 K, respectively. Microscopic origins (e.g., unavoidable defects and oxygen octahedra rotation occurring at a local scale) of such anomalies are suggested. Finally, possible reasons for the facts that some of these dielectric anomalies have not been previously reported in the better studied KTaO3 and SrTiO3 incipient ferroelectrics are also discussed.Comment: 8 pages, 5 figures, submitted to Physical Review