174 research outputs found
Effect of CH addition on excess electron mobility in liquid Kr
The excess electrons mobility has been measured recently in liquid
mixtures of Kr and CH as a function of the electric field up to and of the CH concentration up to at
temperatures fairly close to the normal boiling point of Kr
(folegani). We present here new data which extend the
previous set in the region of low electric field. The experimental results are
interpreted in terms of a kinetic model previously proposed to explain the
concentration dependent behavior of in liquid Ar--Kr and Ar--Xe mixtures.
The main result is that CH is more effective in enhancing
energy--transfer rather than momentum--transfer in comparison with mixtures of
liquified noble gases. The field dependence of is quite complicate. In
particular, at intermediate values of the field, there appears to be a
crossover between two different electric--field dependent behaviors of
The electric field strength at crossover is well correlated with the
concentration of CH This fact suggests that different excitations of the
molecular solute might be involved in the momentum-- and energy--transfer
processes for different values of the mean electron energy.Comment: 17, pages,7 figures, RevTeX4, submitted to J.Chem.Phy
Injection of photoelectrons into dense argon gas
The injection of photoelectrons in a gaseous or liquid sample is a widespread
technique to produce a cold plasma in a weakly--ionized system in order to
study the transport properties of electrons in a dense gas or liquid. We report
here the experimental results of photoelectron injection into dense argon gas
at the temperatureT=142.6 K as a function of the externally applied electric
field and gas density. We show that the experimental data can be interpreted in
terms of the so called Young-Bradbury model only if multiple scattering effects
due to the dense environment are taken into account when computing the
scattering properties and the energetics of the electrons.Comment: 18 pages, 10 figures, figure nr. 10 has been redrawn, to be submitted
to Plasma Sources Science and Technolog
Self-localization of magnon Bose-Einstein condensates in the ground state and on excited levels: from harmonic to box-like trapping potential
Long-lived coherent spin precession of 3He-B at low temperatures around 0.2
Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or
magnons in a magnetic trap which is formed by the order-parameter texture and
can be manipulated experimentally. When the number of magnons increases, the
orbital texture reorients under the influence of the spin-orbit interaction and
the profile of the trap gradually changes from harmonic to a square well, with
walls almost impenetrable to magnons. This is the first experimental example of
Bose condensation in a box. By selective rf pumping the trap can be populated
with a ground-state condensate or one at any of the excited energy levels. In
the latter case the ground state is simultaneously populated by relaxation from
the exited level, forming a system of two coexisting condensates.Comment: 4 pages, 5 figure
Particle detection through the quantum counter concept in YAG:Er
We report about a novel scheme for particle detection based on the infrared
quantum counter concept. Its operation consists of a two-step excitation
process of a four level system, that can be realized in rare earth-doped
crystals when a cw pump laser is tuned to the transition from the second to the
fourth level. The incident particle raises the atoms of the active material
into a low lying, metastable energy state, triggering the absorption of the
pump laser to a higher level. Following a rapid non-radiative decay to a
fluorescent level, an optical signal is observed with a conventional detectors.
In order to demonstrate the feasibility of such a scheme, we have investigated
the emission from the fluorescent level S (540 nm band) in an
Er-doped YAG crystal pumped by a tunable titanium sapphire laser when it
is irradiated with 60 keV electrons delivered by an electron gun. We have
obtained a clear signature this excitation increases the
metastable level population that can efficiently be exploited to generate a
detectable optical signal
Infrared emission spectrum and potentials of and states of Xe excimers produced by electron impact
We present an investigation of the Xe excimer emission spectrum
observed in the near infrared range about 7800 cm in pure Xe gas and in
an Ar (90%) --Xe (10%) mixture and obtained by exciting the gas with energetic
electrons. The Franck--Condon simulation of the spectrum shape suggests that
emission stems from a bound--free molecular transition never studied before.
The states involved are assigned as the bound state with atomic limit and the dissociative state with limit. Comparison with the spectrum simulated by using theoretical
potentials shows that the dissociative one does not reproduce correctly the
spectrum features.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
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State and trait characteristics of anterior insula time-varying functional connectivity.
The human anterior insula (aINS) is a topographically organized brain region, in which ventral portions contribute to socio-emotional function through limbic and autonomic connections, whereas the dorsal aINS contributes to cognitive processes through frontal and parietal connections. Open questions remain, however, regarding how aINS connectivity varies over time. We implemented a novel approach combining seed-to-whole-brain sliding-window functional connectivity MRI and k-means clustering to assess time-varying functional connectivity of aINS subregions. We studied three independent large samples of healthy participants and longitudinal datasets to assess inter- and intra-subject stability, and related aINS time-varying functional connectivity profiles to dispositional empathy. We identified four robust aINS time-varying functional connectivity modes that displayed both "state" and "trait" characteristics: while modes featuring connectivity to sensory regions were modulated by eye closure, modes featuring connectivity to higher cognitive and emotional processing regions were stable over time and related to empathy measures
Studies of a three-stage dark matter and neutrino observatory based on multi-ton combinations of liquid xenon and liquid argon detectors
We study a three stage dark matter and neutrino observatory based on
multi-ton two-phase liquid Xe and Ar detectors with sufficiently low
backgrounds to be sensitive to WIMP dark matter interaction cross sections down
to 10E-47 cm^2, and to provide both identification and two independent
measurements of the WIMP mass through the use of the two target elements in a
5:1 mass ratio, giving an expected similarity of event numbers. The same
detection systems will also allow measurement of the pp solar neutrino
spectrum, the neutrino flux and temperature from a Galactic supernova, and
neutrinoless double beta decay of 136Xe to the lifetime level of 10E27 - 10E28
y corresponding to the Majorana mass predicted from current neutrino
oscillation data. The proposed scheme would be operated in three stages G2, G3,
G4, beginning with fiducial masses 1-ton Xe + 5-ton Ar (G2), progressing to
10-ton Xe + 50-ton Ar (G3) then, dependent on results and performance of the
latter, expandable to 100-ton Xe + 500-ton Ar (G4). This method of scale-up
offers the advantage of utilizing the Ar vessel and ancillary systems of one
stage for the Xe detector of the succeeding stage, requiring only one new
detector vessel at each stage. Simulations show the feasibility of reducing or
rejecting all external and internal background levels to a level <1 events per
year for each succeeding mass level, by utilizing an increasing outer thickness
of target material as self-shielding. The system would, with increasing mass
scale, become increasingly sensitive to annual signal modulation, the agreement
of Xe and Ar results confirming the Galactic origin of the signal. Dark matter
sensitivities for spin-dependent and inelastic interactions are also included,
and we conclude with a discussion of possible further gains from the use of
Xe/Ar mixtures
Energy‐efficient colourless photonic technologies for next‐generation DWDM metro and access networks
Within the scope of our EU FP7 C3PO project, we are developing novel, energy-efficient, colourless photonic technologies for low-cost, next-generation dense wavelength-division-multiplexed metro transport and access networks. The colourless transmitters use reflective arrayed photonic integrated circuits, particularly hybrid reflective electroabsorption modulators, and multi-wavelength laser sources, with custom power-efficient driver circuitry. A low-loss piezoelectric beam-steering optical matrix switch allows for dynamic wavelength reconfigurability. Simplifying the required optical and electronic hardware, as well as avoiding the need for expensive, thermally-stabilised tuneable lasers, will yield cost and energy savings for data switching applications in future metro, access, and datacentre interconnection networks. We report on recent advancement towards these low-power optical networks, providing the latest systems results achieved with key enabling hybrid photonic integrated devices and electronic driver/receiver arrays for our targeted applications
Histone H2AX stabilizes broken DNA strands to suppress chromosome breaks and translocations during V(D)J recombination
The H2AX core histone variant is phosphorylated in chromatin around DNA double strand breaks (DSBs) and functions through unknown mechanisms to suppress antigen receptor locus translocations during V(D)J recombination. Formation of chromosomal coding joins and suppression of translocations involves the ataxia telangiectasia mutated and DNA-dependent protein kinase catalytic subunit serine/threonine kinases, each of which phosphorylates H2AX along cleaved antigen receptor loci. Using Abelson transformed pre–B cell lines, we find that H2AX is not required for coding join formation within chromosomal V(D)J recombination substrates. Yet we show that H2AX is phosphorylated along cleaved Igκ DNA strands and prevents their separation in G1 phase cells and their progression into chromosome breaks and translocations after cellular proliferation. We also show that H2AX prevents chromosome breaks emanating from unrepaired RAG endonuclease-generated TCR-α/δ locus coding ends in primary thymocytes. Our data indicate that histone H2AX suppresses translocations during V(D)J recombination by creating chromatin modifications that stabilize disrupted antigen receptor locus DNA strands to prevent their irreversible dissociation. We propose that such H2AX-dependent mechanisms could function at additional chromosomal locations to facilitate the joining of DNA ends generated by other types of DSBs
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