The recent focus on topological insulators is due to the scientific interest in the new state of quantum matter as well as the technology potential for a new generation of THz optoelectronics, ...spintronics and quantum computations. It is important to elucidate the dynamics of the Dirac fermions in the topologically protected surface state. Hence we utilized a novel ultrafast optical pump mid-infrared probe to explore the dynamics of Dirac fermions near the Dirac point. The femtosecond snapshots of the relaxation process were revealed by the ultrafast optics. Specifically, the Dirac fermion-phonon coupling strength in the Dirac cone was found to increase from 0.08 to 0.19 while Dirac fermions were away from the Dirac point into higher energy states. Further, the energy-resolved transient reflectivity spectra disclosed the energy loss rate of Dirac fermions at room temperature was about 1 meV/ps. These results are crucial to the design of Dirac fermion devices.
The response to stress involves the activation of pathways leading either to protection from the stress origin, eventually resulting in development of stress resistance, or activation of the rapid ...death of the organism. Here we hypothesize that mitochondrial reactive oxygen species (mtROS) play a key role in stress-induced programmed death of the organism, which we called "phenoptosis" in 1997. We demonstrate that the synthetic mitochondria-targeted antioxidant SkQ1 (which specifically abolishes mtROS) prevents rapid death of mice caused by four mechanistically very different shocks: (a) bacterial lipopolysaccharide (LPS) shock, (b) shock in response to intravenous mitochondrial injection, (c) cold shock, and (d) toxic shock caused by the penetrating cation C
TPP. Importantly, under all these stresses mortality was associated with a strong elevation of the levels of pro-inflammatory cytokines and administration of SkQ1 was able to switch off the cytokine storms. Since the main effect of SkQ1 is the neutralization of mtROS, this study provides evidence for the role of mtROS in the activation of innate immune responses mediating stress-induced death of the organism. We propose that SkQ1 may be used clinically to support patients in critical conditions, such as septic shock, extensive trauma, cooling, and severe infection by bacteria or viruses.
We performed a search for a new generic X boson, which could be a scalar (S), pseudoscalar (P), vector (V), or an axial vector (A) particle produced in the 100 GeV electron scattering off nuclei, e− ...Z → e− ZX, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such a process was found in the full NA64 dataset of 2.84 × 1011 electrons on target. We place new bounds on the S, P, V, A coupling strengths to electrons, and set constraints on their contributions to the electron anomalous magnetic moment ae,|ΔaX|≲ 10−15 –10−13 for the X mass region 1 MeV ≲ mX ≲ 1 GeV. These results are an order of magnitude more sensitive compared to the current accuracy on a e from the electron g − 2 experiments and recent high-precision determination of the fine structure constant.
We report theoretical and experimental results of comparison of high-power laser diode arrays made of (Al)GaAs/AlGaAs and GaAsP/GaInP heterostructures for the spectral range from 800 to 810 nm. The ...best results are demonstrated for arrays based on GaAsP/GaInP heterostructures. The maximum values of the output optical power of 1-cm-long laser diode arrays in the quasi-cw pump regime reach 370–380 W. The possible reason for the difference in the output powers of the arrays based on the material systems in question is discussed and methods for further increasing the radiation power are presented.
Thermal dark matter models with particle χ masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble ...interaction between the dark and ordinary matter. We report on a new search for the sub-GeV χ production through the interaction mediated by a new vector boson, called the dark photon A^{'}, in collisions of 100 GeV electrons with the active target of the NA64 experiment at the CERN SPS. With 9.37×10^{11} electrons on target collected during 2016-2022 runs NA64 probes for the first time the well-motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. No evidence for dark matter production has been found. This allows us to set the most sensitive limits on the A^{'} couplings to photons for masses m_{A^{'}}≲0.35 GeV, and to exclude scalar and Majorana dark matter with the χ-A^{'} coupling α_{D}≤0.1 for masses 0.001≲m_{χ}≲0.1 GeV and 3m_{χ}≤m_{A^{'}}.
A two-cascade frequency conversion of CO-laser radiation is demonstrated in a single sample of a nonlinear ZnGeP sub(2) crystal. The crystal is pumped by a repetitively pulsed cryogenic low-pressure ...CO laser operating on ~150 vibration-rotational transitions in the wavelength range 5.0-7.5 mu m, which corresponds to the frequency range of a half octave. In the first conversion cascade, generation of second harmonic and sum frequencies of various pairs of CO-laser radiation give ~350 emission lines in the wavelength range 2.5-3.7 mu m. In the second cascade, by mixing the radiation converted in the first cascade with the residual radiation of the CO laser we have obtained ~90 lines in the range 4.3-5.0 mu m and more than 80 lines in the range 7.5-S.3 mu m. Thus, using a single sample of the nonlinear ZnGeP sub(2) crystal pumped by the radiation of a single CO laser we have produced a source of broadband (more than one and a half octaves) laser radiation, simultaneously operating at ~670 lines in the wavelength range 2.5-8.3 mu m.
The Alaskan Stream is the western boundary current in the subarctic North Pacific. The Alaskan Stream area is characterized by a significant temperature, salinity and density differences between the ...coastal and open-ocean waters and strong mesoscale dynamics. In this paper, we demonstrate the transport pathways of the Alaskan Stream Water in the eastern subarctic Pacific and its extension into the eastern Bering Sea from 1 October 1994 to 12 September 2016 with the help of altimetry-based Lagrangian maps. Mesoscale eddy activity along the boundary between the shelf and deep-basin in the Alaskan Stream region and the eastern Bering Sea is shown to be related to the wind stress curl in the northern North Pacific in winter. A significant correlation is found between the concentration of chlorophyll a in the Alaskan Stream area and eastern Bering Sea in August–September and the wind stress curl in the northern North Pacific in November–March. The mesoscale dynamics, forced by the wind stress curl in winter, may influence not only lower trophic-level organism biomass but also salmon abundance and catch in the study area.
•Temperature dependences of ZnGeP2 crystal indices.•Broadband sum frequency generation at various ZnGeP2 crystal temperatures.•Spectrum tuning by the crystal temperature changing.•Dynamic crystal ...heating under broadband frequency conversion.
Temperature dependences of nonlinear ZnGeP2 crystal indices within the wavelength range of 5.0–6.2 μm (around noncritical spectral phase-matching) were examined with a frequency-selective Q-switched CO laser. The correct dependences were found and applied for numerical study of the spectrum tuning by the crystal temperature changing under the broadband CO laser sum frequency generation. The latter was experimentally studied for the crystal temperature range from the room one up to 145 °C. Requirements for ZnGeP2 crystal temperature changing needed for broadband frequency conversion of 5–7.5 μm radiation were formulated.
We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super ...Proton Synchrotron with a momentum of 160 GeV / c are directed to an active target. The signal signature consists of a single scattered muon with momentum < 80 GeV / c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of ( 1.98 ± 0.02 ) × 10 10 muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining ( m Z ′ , g Z ′ ) parameter space of a new Z ′ ( L μ − L τ ) vector boson which could explain the muon ( g − 2 ) μ anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments. Published by the American Physical Society 2024
Spectral-temperature dependences of the refractive indices of nonlinear LBO crystals 30 × 30 × 10 mm
3
in size are derived by terahertz time-domain spectroscopy in the 0.05–0.5-THz range upon heating ...from 20 to 200°C. Intersection of the spectral dependences of the refractive index components
n
x
and
n
y
is found at ∼84°C. The results can be used for selection of types and phase-matching conditions for frequency conversion into the long-wavelength part of the THz region, which is promising for monitoring the gas composition of the atmosphere due to the low sensitivity to aerosol attenuation.
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