8,631 research outputs found
Electron effective mass in AlGaN alloys determined by mid-infrared optical Hall effect
The effective electron mass parameter in Si-doped AlGaN is
determined to be from mid-infrared optical Hall
effect measurements. No significant anisotropy of the effective electron mass
parameter is found supporting theoretical predictions. Assuming a linear change
of the effective electron mass with the Al content in AlGaN alloys and
for GaN, an average effective electron mass of
can be extrapolated for AlN. The analysis of mid-infrared
spectroscopic ellipsometry measurements further confirms the two phonon mode
behavior of the E(TO) and one phonon mode behavior of the A(LO) phonon
mode in high-Al-content AlGaN alloys as seen in previous Raman scattering
studies
Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies
The effect of a tunable, externally coupled Fabry-P\'{e}rot cavity to
resonantly enhance the optical Hall effect signatures at terahertz frequencies
produced by a traditional Drude-like two-dimensional electron gas is shown and
discussed in this communication. As a result, the detection of optical Hall
effect signatures at conveniently obtainable magnetic fields, for example by
neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high electron
mobility transistor structure grown on a sapphire substrate is used for the
experiment. The optical Hall effect signatures and their dispersions, which are
governed by the frequency and the reflectance minima and maxima of the
externally coupled Fabry-P\'{e}rot cavity, are presented and discussed. Tuning
the externally coupled Fabry-P\'{e}rot cavity strongly modifies the optical
Hall effect signatures, which provides a new degree of freedom for optical Hall
effect experiments in addition to frequency, angle of incidence and magnetic
field direction and strength
Water relations of grapevine cv. Cortese with different training systems
Leaf (LWP) and stem water potential and stomatal conductance (SC) were measured during the day on grapevines trained with four different systems: traditional trellis, central curtain, Y trellis and double curtain. During most of the day LWP was lower and the stem to leaf water potential gradient was higher in the traditional trellis than in the other systems. On the contrary, very few differences were found as regards SC. Osmotic potential changed little during the day and among treatments. Traditional trellis vines had lower yield and total sugar production. The conclusion is drawn that training systems can affect water relations and in this way influence yield and must quality.Relations hydriques de vignes du cépage Cortese élevées sous différents systèmes de conduiteLe potentiel hydrique des feuilles (LWP) et des tiges et la conductance stomatique (SC) ont été mésurés le long du jour sur des plantes de vigne élevés sous quatre systèmes de conduite: vigne palissée en taille Guyot, rideau simple, système Y, rideau double. Pendant la plupart du jour LWP a été plus réduit dans les vignes en Guyot tandis que le gradient de potentiel entre feuille et tige a été plus éléve chez le même système de conduite. Au contraire, les différences au niveau de SC ont été négligeables. Le potentiel osmotique de la feuille a peu changé le long du jour et entre les systemès de conduite. Les vignes en Guyot ont produit moins de raisins et de sucre. Le mode de conduite peut affecter les relations hydriques de la vigne et donc modifier la production et la qualité du moût
Free-charge carrier parameters of n-type, p-type and compensated InN:Mg determined by Infrared Spectroscopic Ellipsometry
Infrared spectroscopic ellipsometry is applied to investigate the free-charge
carrier properties of Mg-doped InN films. Two representative sets of In-polar
InN grown by molecular beam epitaxy with Mg concentrations ranging from
cm to cm are compared. P-type
conductivity is indicated for the Mg concentration range of
cm to cm from a systematic investigation of the
longitudinal optical phonon plasmon broadening and the mobility parameter in
dependence of the Mg concentration. A parameterized model that accounts for the
phonon-plasmon coupling is applied to determine the free-charge carrier
concentration and mobility parameters in the doped bulk InN layer as well as
the GaN template and undoped InN buffer layer for each sample. The free-charge
carrier properties in the second sample set are consistent with the results
determined in a comprehensive analysis of the first sample set reported earlier
[Sch\"oche et al., J. Appl. Phys. 113, 013502 (2013)]. In the second set, two
samples with Mg concentration of cm are identified as
compensated n-type InN with very low electron concentrations which are suitable
for further investigation of intrinsic material properties that are typically
governed by high electron concentrations even in undoped InN. The compensated
n-type InN samples can be clearly distinguished from the p-type conductive
material of similar plasma frequencies by strongly reduced phonon plasmon
broadening
Cell cycle-dependent phosphorylation of Theileria annulata schizont surface proteins
The invasion of Theileria sporozoites into bovine leukocytes is rapidly followed by the destruction of the surrounding host cell membrane, allowing the parasite to establish its niche within the host cell cytoplasm. Theileria infection induces host cell transformation, characterised by increased host cell proliferation and invasiveness, and the activation of anti-apoptotic genes. This process is strictly dependent on the presence of a viable parasite. Several host cell kinases, including PI3-K, JNK, CK2 and Src-family kinases, are constitutively activated in Theileria-infected cells and contribute to the transformed phenotype. Although a number of host cell molecules, including IkB kinase and polo-like kinase 1 (Plk1), are recruited to the schizont surface, very little is known about the schizont molecules involved in host-parasite interactions. In this study we used immunofluorescence to detect phosphorylated threonine (p-Thr), serine (p-Ser) and threonine-proline (p-Thr-Pro) epitopes on the schizont during host cell cycle progression, revealing extensive schizont phosphorylation during host cell interphase. Furthermore, we established a quick protocol to isolate schizonts from infected macrophages following synchronisation in S-phase or mitosis, and used mass spectrometry to detect phosphorylated schizont proteins. In total, 65 phosphorylated Theileria proteins were detected, 15 of which are potentially secreted or expressed on the surface of the schizont and thus may be targets for host cell kinases. In particular, we describe the cell cycle-dependent phosphorylation of two T. annulata surface proteins, TaSP and p104, both of which are highly phosphorylated during host cell S-phase. TaSP and p104 are involved in mediating interactions between the parasite and the host cell cytoskeleton, which is crucial for the persistence of the parasite within the dividing host cell and the maintenance of the transformed state
How do wave packets spread? Time evolution on Ehrenfest time scales
We derive an extension of the standard time dependent WKB theory which can be
applied to propagate coherent states and other strongly localised states for
long times. It allows in particular to give a uniform description of the
transformation from a localised coherent state to a delocalised Lagrangian
state which takes place at the Ehrenfest time. The main new ingredient is a
metaplectic operator which is used to modify the initial state in a way that
standard time dependent WKB can then be applied for the propagation.
We give a detailed analysis of the phase space geometry underlying this
construction and use this to determine the range of validity of the new method.
Several examples are used to illustrate and test the scheme and two
applications are discussed: (i) For scattering of a wave packet on a barrier
near the critical energy we can derive uniform approximations for the
transition from reflection to transmission. (ii) A wave packet propagated along
a hyperbolic trajectory becomes a Lagrangian state associated with the unstable
manifold at the Ehrenfest time, this is illustrated with the kicked harmonic
oscillator.Comment: 30 pages, 3 figure
The Two-Loop Euler-Heisenberg Lagrangian in Dimensional Renormalization
We clarify a discrepancy between two previous calculations of the two-loop
QED Euler-Heisenberg Lagrangian, both performed in proper-time regularization,
by calculating this quantity in dimensional regularization.Comment: 12 pages, standard Latex, no figures, uses a4wide.st
Process Combination of VPP-LED and Vacuum Die Casting for Producing Complex Ceramic 3D-MID
Future developments lead to increasing demands on mechatronic integrated devices (MID). Therefore, ceramics have to be used as substrate material and conductor tracks have to be located in the interior of components to be sufficiently protected. A process combination of vat photopolymerization (VPP-LED) and vacuum die casting is investigated for realizing such structures. First, optimized process parameters are derived by studying the filling behavior of straight capillaries. Subsequently, the results are transferred to complex additively manufactured substrates to derive design guidelines
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