114 research outputs found
New Neutron Lifetime Measurements with the Big Gravitational Trap and Review of Neutron Lifetime Data
Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. In our experiment we measure the storage time of UCN in the material trap coated with a hydrogen-free fluorine-containing polymer (Fomblin grease UT-18). The stability of this coating to multiple thermal cycles between 80 K and 300 K was tested. The achieved storage time is only 1.5% less than free neutron lifetime. Using additional surface, which can be plunged into the trap to change the collision frequency of UCN with walls, we calculate free neutron lifetime by extrapolation to zero collision frequency. The result of the measurements with this new experimental setup i
Soft X-ray harmonic comb from relativistic electron spikes
We demonstrate a new high-order harmonic generation mechanism reaching the
`water window' spectral region in experiments with multi-terawatt femtosecond
lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving
uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron
spike formed at the joint of the boundaries of a cavity and bow wave created by
a relativistically self-focusing laser in underdense plasma. The spike
sharpness and stability are explained by catastrophe theory. The mechanism is
corroborated by particle-in-cell simulations
Search for macroscopic CP violating forces using a neutron EDM spectrometer
The search for CP violating forces between nucleons in the so-called axion
window of force ranges lam between 2x10^-5 m and 0.02 m is interesting because
only little experimental information is available there. Axion-like particles
would induce a pseudo-magnetic field for neutrons close to bulk matter. A
laboratory search investigates neutron spin precession close to a heavy mirror
using ultracold neutrons in a magnetic resonance spectrometer. From the absence
of a shift of the magnetic resonance we established new constraints on the
coupling strength of axion-like particles in terms of the product gs x gp of
scalar and pseudo-scalar dimensionless constants, as a function of the force
range lam, gs x gp x lam^2 <= 2x10-21 [cm^2] (C.L.95%) for 10^-4 cm < lam < 1
cm. For 0.1 cm < lam < 1 cm previous limits are improved by 4 to 5 orders of
magnitude.Comment: 10 pages, 3 figure
High-order alloharmonics produced by nonperiodic drivers
High-order harmonics are ubiquitous in nature and present in electromagnetic,
acoustic, and gravitational waves. They are generated by periodic nonlinear
processes or periodic high-frequency pulses. However, this periodicity is often
inexact, such as that in chirped (frequency-swept) optical waveforms or
interactions with nonstationary matter -- for instance, reflection from
accelerating mirrors. Spectra observed in such cases contain complicated sets
of harmonic-like fringes. We encountered such fringes in our experiment on
coherent extreme ultraviolet generation via BISER, and could not interpret them
using currently available knowledge. Here, we present a comprehensive theory
based on interference of harmonics with different orders fully explaining the
formation of these fringes, which we call alloharmonics. Like atomic spectra,
the complex alloharmonic spectra depend on several integer numbers and bear a
unique imprint of the emission process, which the theory can decipher, avoiding
confusion or misinterpretation. We also demonstrate the alloharmonics in
simulations of gravitational waves emitted by binary black hole mergers.
Further, we predict the presence of alloharmonics in the radio spectra of
pulsars and in optical frequency combs, and propose their use for measurement
of extremely small accelerations necessary for testing gravity theories. The
alloharmonics phenomenon generalizes classical harmonics and is critical in
research fields such as laser mode locking, frequency comb generation,
attosecond pulse generation, pulsar studies, and future gravitational wave
spectroscopy.Comment: 29 pages, 9 figures, 3 table
X-ray spectroscopy of super-intense laser-produced plasmas for the study of nonlinear processes. Comparison with PIC simulations
We present X-ray spectroscopic diagnostics in femto-second laser-driven experiments revealing nonlinear phenomena caused by the strong coupling of the laser radiation with the created plasma. Among those nonlinear phenomena, we found the signatures of the Two Plasmon Decay (TPD) instability in a laser-driven CO2 cluster-based plasma by analyzing the Langmuir dips in the profile of the O VIII Lyϵ line, caused by the Langmuir waves created at the high laser intensity 3 1018Wcm-2. With similar laser intensities, we reveal also the nonlinear phenomenon of the Second Harmonic Generation (SHG) of the laser frequency by analyzing the nonlinear phenomenon of satellites of Lyman δ and ϵ lines of Ar XVII. In the case of relativistic laser-plasma interaction we discovered the Parametric Decay Instability (PDI)-induced ion acoustic turbulence produced simultaneously with Langmuir waves via irradiation of thin Si foils by laser intensities of 1021Wcm-2
X-ray harmonic comb from relativistic electron spikes
X-ray devices are far superior to optical ones for providing nanometre
spatial and attosecond temporal resolutions. Such resolution is indispensable
in biology, medicine, physics, material sciences, and their applications. A
bright ultrafast coherent X-ray source is highly desirable, for example, for
the diffractive imaging of individual large molecules, viruses, or cells. Here
we demonstrate experimentally a new compact X-ray source involving high-order
harmonics produced by a relativistic-irradiance femtosecond laser in a gas
target. In our first implementation using a 9 Terawatt laser, coherent soft
X-rays are emitted with a comb-like spectrum reaching the 'water window' range.
The generation mechanism is robust being based on phenomena inherent in
relativistic laser plasmas: self-focusing, nonlinear wave generation
accompanied by electron density singularities, and collective radiation by a
compact electric charge. The formation of singularities (electron density
spikes) is described by the elegant mathematical catastrophe theory, which
explains sudden changes in various complex systems, from physics to social
sciences. The new X-ray source has advantageous scalings, as the maximum
harmonic order is proportional to the cube of the laser amplitude enhanced by
relativistic self-focusing in plasma. This allows straightforward extension of
the coherent X-ray generation to the keV and tens of keV spectral regions. The
implemented X-ray source is remarkably easily accessible: the requirements for
the laser can be met in a university-scale laboratory, the gas jet is a
replenishable debris-free target, and the harmonics emanate directly from the
gas jet without additional devices. Our results open the way to a compact
coherent ultrashort brilliant X-ray source with single shot and high-repetition
rate capabilities, suitable for numerous applications and diagnostics in many
research fields
Immunogenicity evaluation of Gam-COVID-Vac (Sputnik V)
In November 2020, the Armed Forces of the Russian Federation began mass immunisation of the personnel with Gam-COVID-Vac (Sputnik V), the first Russia vaccine against the new coronavirus infection (COVID-19). Thus, it became necessary to assess post-vaccination antibody levels and the duration and intensity of humoral immunity to COVID-19.The aim of the study was to investigate the immunogenicity and efficacy of Gam-COVID-Vac in military medical staff after vaccination.Materials and methods: the authors determined the presence of specific antibodies in the serum of individuals immunised with Gam-COVID-Vac (477 volunteers) and COVID-19 convalescents (73 patients), using virus neutralisation (VN), enzyme-linked immunosorbent assay (ELISA) with reagent kits by several manufacturers, and immunoblotting. The results of the study were evaluated using analysis of variance.Results: VN detected virus neutralising antibodies in 90.7% of vaccinated subjects; ELISA, in 95.4%. Both VN and ELISA showed lower antibody levels in the vaccinated over 50 years of age. ELISA demonstrated a significantly higher concentration of anti-SARS-CoV-2 spike IgG in the Gam-COVID-Vac group than in the COVID-19 convalescent group. The correlation between antibody detection results by VN and ELISA was the strongest when the authors used their experimental reagent kit for quantitative detection of virus neutralising antibodies by competitive ELISA with the recombinant human ACE2 receptor. Having analysed the time course of neutralising antibody titres, the authors noted a significant, more than two-fold decrease in geometric means of the titres three months after administration of the second vaccine component.Conclusions: the subjects vaccinated with Gam-COVID-Vac gain effective humoral immunity to COVID-19. The decrease in titres indicates the need for revaccination in 6 months
- …