Free carrier effects in gallium nitride epilayers: the valence band dispersion

The dispersion of the A-valence-band in GaN has been deduced from the observation of high-index magneto-excitonic states in polarised interband magneto-reflectivity and is found to be strongly non-parabolic with a mass in the range 1.2-1.8 m_{e}. It matches the theory of Kim et al. [Phys. Rev. B 56, 7363 (1997)] extremely well, which also gives a strong k-dependent A-valence-band mass. A strong phonon coupling leads to quenching of the observed transitions at an LO-phonon energy above the band gap and a strong non-parabolicity. The valence band was deduced from subtracting from the reduced dispersion the electron contribution with a model that includes a full treatment of the electron-phonon interaction.Comment: Revtex, 4 pages, 5 figure

Tunnelling Studies of Two-Dimensional States in Semiconductors with Inverted Band Structure: Spin-orbit Splitting, Resonant Broadening

The results of tunnelling studies of the energy spectrum of two-dimensional (2D) states in a surface quantum well in a semiconductor with inverted band structure are presented. The energy dependence of quasimomentum of the 2D states over a wide energy range is obtained from the analysis of tunnelling conductivity oscillations in a quantizing magnetic field. The spin-orbit splitting of the energy spectrum of 2D states, due to inversion asymmetry of the surface quantum well, and the broadening of 2D states at the energies, when they are in resonance with the heavy hole valence band, are investigated in structures with different strength of the surface quantum well. A quantitative analysis is carried out within the framework of the Kane model of the energy spectrum. The theoretical results are in good agreement with the tunnelling spectroscopy data.Comment: 29 pages, RevTeX, submitted in Phys.Rev.B. Figures available on request from [email protected]

Flight of the dragonflies and damselflies

This work is a synthesis of our current understanding of the mechanics, aerodynamics and visually mediated control of dragonfly and damselfly flight, with the addition of new experimental and computational data in several key areas. These are: the diversity of dragonfly wing morphologies, the aerodynamics of gliding flight, force generation in flapping flight, aerodynamic efficiency, comparative flight performance and pursuit strategies during predatory and territorial flights. New data are set in context by brief reviews covering anatomy at several scales, insect aerodynamics, neuromechanics and behaviour. We achieve a new perspective by means of a diverse range of techniques, including laser-line mapping of wing topographies, computational fluid dynamics simulations of finely detailed wing geometries, quantitative imaging using particle image velocimetry of on-wing and wake flow patterns, classical aerodynamic theory, photography in the field, infrared motion capture and multi-camera optical tracking of free flight trajectories in laboratory environments. Our comprehensive approach enables a novel synthesis of datasets and subfields that integrates many aspects of flight from the neurobiology of the compound eye, through the aeromechanical interface with the surrounding fluid, to flight performance under cruising and higher-energy behavioural modes

Increased levels of VEGF-C and macrophage infiltration in lipedema patients without changes in lymphatic vascular morphology

Lipedema is a chronic adipose tissue disorder characterized by the disproportional subcutaneous deposition of fat and is commonly misdiagnosed as lymphedema or obesity. The molecular determinants of the lipedema remain largely unknown and only speculations exist regarding the lymphatic system involvement. The aim of the present study is to characterize the lymphatic vascular involvement in established lipedema. The histological and molecular characterization was conducted on anatomically-matched skin and fat biopsies as well as serum samples from eleven lipedema and ten BMI-matched healthy patients. Increased systemic levels of vascular endothelial growth factor (VEGF)-C (P=0.02) were identified in the serum of lipedema patients. Surprisingly, despite the increased VEGF-C levels no morphological changes of the lymphatic vessels were observed. Importantly, expression analysis of lymphatic and blood vessel-related genes revealed a marked downregulation of Tie2 (P<0.0001) and FLT4 (VEGFR-3) (P=0.02) consistent with an increased macrophage infiltration (P=0.009), without changes in the expression of other lymphatic markers. Interestingly, a distinct local cytokine milieu, with decreased VEGF-A (P=0.04) and VEGF-D (P=0.02) expression was identified. No apparent lymphatic anomaly underlies lipedema, providing evidence for the different disease nature in comparison to lymphedema. The changes in the lymphatic-related cytokine milieu might be related to a modified vascular permeability developed secondarily to lipedema progression

Generation of an ultrabroadband supercontinuum in the mid-infrared region using dispersion-engineered GeAsSe photonic crystal fiber

An ultrabroadband mid-infrared (MIR) region supercontinuum (SC) is demonstrated numerically through dispersion-engineered traditional chalcogenide (ChG) photonic crystal fiber (PCF). By varying structural parameters pitch (hole to hole spacing) and air-hole diameter to pitch ratio, a number of 10-mm-long hexagonal PCFs made employing GeAsSe ChG glass as a core and air-holes of hexagonal lattice running through their lengths as a cladding are optimized to predict an efficient mid-infrared region SC spectral emission by pumping them using a tunable pump source between 2.9 and 3.3 µm. Simulations are carried out using an ultrashort pump pulse of 100-fs duration with a low pulse peak powers of between 3 and 4 kW into the optimized designs. It is found through numerical analysis that efficient SC spectral broadening with flattened output can be obtained by increasing the PCF pitch rather than increasing the PCF cladding containing air-hole diameter although a larger nonlinear coefficient could be obtained through increasing air-hole diameter of an optimized design. Simulation results show that the SC spectra can be broadened up to 12.2 µm for a certain design with a peak power of 3 kW. Using a peak power of 4 kW, it is possible to obtain SC spectral broadening beyond 14 µm with an optimized design spanning the wavelength range from 1.8 to 14 µm which covers the electromagnetic spectrum required for MIR molecular fingerprint region applications such as sensing and biological imaging

The ELBA Force Field for Coarse-Grain Modeling of Lipid Membranes

A new coarse-grain model for molecular dynamics simulation of lipid membranes is presented. Following a simple and conventional approach, lipid molecules are modeled by spherical sites, each representing a group of several atoms. In contrast to common coarse-grain methods, two original (interdependent) features are here adopted. First, the main electrostatics are modeled explicitly by charges and dipoles, which interact realistically through a relative dielectric constant of unity (). Second, water molecules are represented individually through a new parametrization of the simple Stockmayer potential for polar fluids; each water molecule is therefore described by a single spherical site embedded with a point dipole. The force field is shown to accurately reproduce the main physical properties of single-species phospholipid bilayers comprising dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylethanolamine (DOPE) in the liquid crystal phase, as well as distearoylphosphatidylcholine (DSPC) in the liquid crystal and gel phases. Insights are presented into fundamental properties and phenomena that can be difficult or impossible to study with alternative computational or experimental methods. For example, we investigate the internal pressure distribution, dipole potential, lipid diffusion, and spontaneous self-assembly. Simulations lasting up to 1.5 microseconds were conducted for systems of different sizes (128, 512 and 1058 lipids); this also allowed us to identify size-dependent artifacts that are expected to affect membrane simulations in general. Future extensions and applications are discussed, particularly in relation to the methodology's inherent multiscale capabilities

Wpływ warunków tlenowych w glebie na masę i skład mineralny korzeni soi i żyta ozimego

The changes of the N, P, K, Ca, Mg and Na content in the roots of winter rye and soybean subjected to oxygen stresses for the period of 2 weeks during 3 stages of their development have been examined.L'objectif de ce travail a été d'étudièr l'effet des conditions d'oxygène, en trois phases de développement du seigle d'hiver (Secale cereale c.v. Dańkowskie Nowe) et du soya (Glicyne hispida Max. c.v. Progres) sur la masse des racines et la teneur en N, P, K, Ca, Mg et Na. L'expérience a enfermé 6 cycles d'etudes, effectuées dans les essais en vases, au cours des années 1982-1985. Dans chaque cycle d'essais on s'est servi de 84 vases de 6 dm³ dont chacun contenait 6,5 kg de sol brun formé du loess. Les conditions d'oxygène du sol ont été modifiées à l'aide de deux facteurs physiques fondamentaux, changeants au champ, c'est-à-dire l'humidité et la compacité du sol. On a appliqué le compactage 1,2; 1,35 et 1,50 Mg·m⁻³. Outre l'humidité témoin au niveau de 80-15 kPa, on a appliqué l'humidité du sol qui correspondait à la succion 2-5 et 0 kPa. Le seigle a été soumis au stress d'oxygène dans les phases suivantes du développement: 1) phase de l-2e feuille (plantes de 12 jours), 2) phase de montaison, 3) phase d'épiaison. Dans le cas du soya, les stress d'oxygène ont été appliqués dans les phases suivantes: 1) phase de floraison, 2) phase de formation des casses, 3) phase de développement des cosses et de mûrissement des semences. Pour les mesures ODR on s'est servi des électrodes en platine, le temps de polarisation de l'électrode 4 min. et la tension -0,65 V. Le déficit d'oxygène pour les racines du seigle d'hiver, pendant la période de deux semaines, a entraîné la diminution de la masse sèche de racines à maturité pleine (jusqu'à 30 %), l'augmentation de la teneur en Na et la diminution du prélèvement de N, P, K, Na et Ca. Ces changements ont été observés à ODR au-dessous de 20-30 µg·m⁻²·s⁻¹. Dans le cas de soya, ces stress hydriques n'entraînaient que l'augmentation de la teneur en K et Na a ODR < 20 µg·m⁻²·s⁻¹.Celem pracy było zbadanie wpływu warunków tlenowych w glebie w trzech fazach rozwojowych żyta ozimego (Secale cereale c.v. Dańkowskie Nowe) i soi (Glycine hispida Max.c.v. Progres) na masę korzeni i zawartość N, P, K, Ca, Mg i Na. Całość eksperymentu obejmowała 6 cykli badawczych przeprowadzonych w doświadczeniu wazonowym w latach 1982-1985. Każdy cykl doświadczalny obejmował 84 wazony o poj. 6 dm³, w których umieszczono po 6,5 kg gleby brunatnej wytworzonej z lessu. Warunki tlenowe w glebie różnicowano za pomocą dwóch podstawowych czynników fizycznych zmieniających się w warunkach polowych, tj. uwilgotnienia i zagęszczenia gleby. Stosowano zagęszczenia 1,2; 1,35 i 1,50 Mg·m⁻³. Oprócz wilgotności kontrolnej na poziomie 80-15 kPa, stosowano uwilgotnienie gleby odpowiadające ciśnieniu ssącemu 2-5 i 0 kPa. Żyto poddawane było stresom tlenowym w następujących fazach rozwojowych; I - faza 1-2 listka (12-dniowe rośliny), II - faza strzelania w źdźbło, III - faza kłoszenia. W przypadku soi stosowano stresy tlenowe w fazach rozwojowych: I - faza kwitnienia roślin, II - faza tworzenia się strąków, III - faza wypełniania się strąków i dojrzewania nasion. Do pomiarów ODR używano elektrod platynowych, czas polaryzacji elektrody wynosił 4 min., a napięcie -0,65 V. Niedotlenienie korzeni żyta ozimego przez okres dwu tygodni powodowało zmniejszenie suchej masy korzeni w stanie dojrzałości pełnej (do 30%), wzrost zawartości Na oraz zmniejszenie pobrania N, P, K, Na i Ca. Zmiany te obserwowano zazwyczaj przy ODR poniżej 20-30 µg·m⁻²·s⁻¹. Podobne stresy tlenowe u soi powodowały jedynie podwyższenie zawartości K i Na przy ODR < 20 µg·m⁻²·s⁻¹