7,664 research outputs found
On the low energy limit of one loop photon-graviton amplitudes
We present first results of a systematic study of the structure of the low
energy limit of the one-loop photon-graviton amplitudes induced by massive
scalars and spinors. Our main objective is the search of KLT-type relations
where effectively two photons merge into a graviton. We find such a relation at
the graviton-photon-photon level. We also derive the diffeomorphism Ward
identity for the 1PI one graviton - N photon amplitudes.Comment: 14 pages, 1 figure. Final version to be published in Physics Letters
Dielectric constants and phonon modes of amorphous hafnium aluminate deposited by metal organic chemical vapor deposition
Dielectric constants and long-wavelength optical phonon modes of amorphous hafnium aluminate films with a maximum aluminum content of 19 at. % are studied by infrared spectroscopic ellipsometry (IRSE). The hafnium aluminate films were prepared by metal organic chemical vapor deposition on silicon substrates. IRSE revealed one polar lattice mode and one impurity-type mode, which show all a systematic shift in frequency with varying Al content. The static dielectric constant decreases from 10.1 for 4.6 at. % Al to 8.1 for 19 at. % Al. The absolute values were found to be between 50% and 70% smaller than the values obtained from electrical measurements
Ultrasonic Testing of Rails Including Vertical Cracks - Numerical Modeling and Experimental Results
One of the possible reasons for the failure of rails in railway tracks is the appearance of vertical cracks in the head, neck or bottom of the rail (see Fig. 1). Therefore, it is necessary to detect such defects at an early stage when the cracks are still of smaller dimensions. For vertical cracks, results of ultrasonic pulse-echo measurements are difficult to interpret due to mode conversions at the crack and rail surfaces, respectively. For normal incidence, not only the attenuation of the primary wavefront but also new echoes due to converted wave modes can be observed in the A-scan data
3D printing of ultraâthin veneers made of lithium disilicate using the LCM method in a digital workflow: A feasibility study
Objective
This article highlights the feasibility of the additive fabrication of ultra-thin veneers made of lithium disilicate using the lithography-based ceramic manufacturing (LCM) method.
Clinical Considerations
An esthetical appealing restoration of anterior teeth with thin ceramic veneers is considered one of the ultimate challenges in restorative dental prosthetics. These sophisticated restorations can be fabricated in different ways. Both analog and digital subtractive manufacturing processes have been used to date. Either of the methods is highly demanding for the dental technician and dental engineering due to the required low ceramic layer thickness.
Conclusion
Modern additive manufacturing methods, for example LCM technology, enable the production of ultra-thin lithium disilicate veneers with layer thicknesses of down to 0.2âmm and could therefore represent a viable alternative for this indication in the future.
Clinical Significance
Digital technologies can help streamline workflows, make the outcome more predictable and reproducible, and even further optimize therapeutic restorative options such as highly esthetic veneers for anterior teeth. The reduced material thickness allows for a true non-prep solution or minimally invasive preparation
Effect of different N fertilization of vine on the tryptophan, free and total indole-3-acetic acid concentrations
The compound responsible for UTA (untypical ageing off-flavour) in wines is o-AAP (o-amino acetophenone). It is formed from IAA (indole-3-acetic acid), triggered by sulfurylation. The aim of this study was to evaluate the effect of different N fertilizer supply on this precursor in must and wine, making use of a long-term nitrogen fertilization experiment. Trp (Tryptophan) as well as free and conjugated IAA were determined in musts and wines produced from grapevines supplied with 0, 30, 60, 90 or 150 kg N ha-1 year-1. IAA concentrations in musts and wines varied highly over years (1994-1999), wines containing about half of the total IAA of musts. The IAA concentration in must was positively correlated with the concentration of amino acids in must, however, nitrogen supply did not have any effect, neither on Trp nor on IAA concentrations
Real-time observation of interfering crystal electrons in high-harmonic generation
Accelerating and colliding particles has been a key strategy to explore the
texture of matter. Strong lightwaves can control and recollide electronic
wavepackets, generating high-harmonic (HH) radiation which encodes the
structure and dynamics of atoms and molecules and lays the foundations of
attosecond science. The recent discovery of HH generation in bulk solids
combines the idea of ultrafast acceleration with complex condensed matter
systems and sparks hope for compact solid-state attosecond sources and
electronics at optical frequencies. Yet the underlying quantum motion has not
been observable in real time. Here, we study HH generation in a bulk solid
directly in the time-domain, revealing a new quality of strong-field
excitations in the crystal. Unlike established atomic sources, our solid emits
HH radiation as a sequence of subcycle bursts which coincide temporally with
the field crests of one polarity of the driving terahertz waveform. We show
that these features hallmark a novel non-perturbative quantum interference
involving electrons from multiple valence bands. The results identify key
mechanisms for future solid-state attosecond sources and next-generation
lightwave electronics. The new quantum interference justifies the hope for
all-optical bandstructure reconstruction and lays the foundation for possible
quantum logic operations at optical clock rates
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
Non-perturbative Interband Response of InSb Driven Off-resonantly by Few-cycle Electromagnetic Transients
Intense multi-THz pulses are used to study the coherent nonlinear response of
bulk InSb by means of field-resolved four-wave mixing spectroscopy. At
amplitudes above 5 MV/cm the signals show a clear temporal substructure which
is unexpected in perturbative nonlinear optics. Simulations based on a
two-level quantum system demonstrate that in spite of the strongly off-resonant
character of the excitation the high-field pulses drive the interband
resonances into a non-perturbative regime of Rabi flopping.Comment: 4 pages, 4 figure
Effects of vesicular-arbuscular mycorrhizal fungi on micropropagated grapevines: Influence of endophyte strain, P fertilization and growth medium
EinfluĂ vesikulĂ€r-arbuskulĂ€rer Mykorrhizapilze auf in vitro vermehrte Reben: Wirkung von Pilzstamm, PhosphatdĂŒngung und KultursubstratIn vitro vermehrte Pflanzen der Unterlagssorte Vitis berlandieri x V. rupestris 1103 P wurden in steriles Substrat verpflanzt, das mit steigenden P-Gaben angereichert war, und wĂ€hrend der Anpassungsphase mit verschiedenen Arten vesikulĂ€r-arbuskulĂ€rer Mykorrhizapilze (VAM) beimpft. In dem Substrat ohne P-DĂŒngung förderten alle Pilzarten das Rebenwachstum; der positive EinfluĂ der Beimpfung war jedoch mit zunehmender DĂŒngungsstufe verwischt. Zwei Pilzarten waren indessen auch noch bei der höchsten P-Konzentration in der Lage, das Pflanzenwachstum zu steigern. In einem weiteren Versuch wurde der EinfluĂ der VAM-Art Glomus caledonicum (NICOL. et GERD.) TRAPPE et GERD. in einem Torf/Sand-Gemisch geprĂŒft, das mit 0 oder 10 % Erde versetzt war. Obwohl der VAM-Pilz die Wurzeln in beiden FĂ€llen besiedelte, wurde eine signifikante Wachstumssteigerung nur in dem Erde enthaltenden Substrat festgestellt
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