1,375 research outputs found
Improved electrodes for skin contacts
Design is described of thick, flexible electrodes with appropriate metal surfaces which prevent unnecessary skin motion. Electrodes provide sufficient radial pressure directed toward body surface to depress skin a noticeable portion of its normal resilient thickness
Decaying warm dark matter and neutrino masses
Neutrino masses may arise from spontaneous breaking of ungauged lepton
number. Due to quantum gravity effects the associated Goldstone boson - the
majoron - will pick up a mass. We determine the lifetime and mass required by
cosmic microwave background observations so that the massive majoron provides
the observed dark matter of the Universe. The majoron DDM scenario fits nicely
in models where neutrino masses arise a la seesaw, and may lead to other
possible cosmological implications.Comment: 4 pages, 3 figures. Replaced to match published version. Minor
changes made to address referees' comments. References adde
Submillimeter Spectrum of Formic Acid
We have measured new submillimeter-wave data around 600 GHz and around 1.1
THz for the 13C isotopologue of formic acid and for the two deuterium
isotopomers; in each case for both the trans and cis rotamer. For cis-DCOOH and
cis-HCOOD in particular only data up to 50 GHz was previously available. For
all species the quality and quantity of molecular parameters has been increased
providing new measured frequencies and more precise and reliable frequencies in
the range of existing and near-future submillimeter and far-infrared
astronomical spectroscopy instruments such as Herschel, SOFIA and ALMA
Rotational Spectrum of the Formyl Cation, HCO+, to 1.2 THz
A variety of high-quality spectroscopic studies have contributed to knowledge of the formyl cation, HCO+, and its rare isotopologues, but technical limitations have previously limited precise determinations of the far-infrared, or terahertz spectrum. This study extends the microwave, millimeter, and submillimeter spectroscopy of HCO+ into the terahertz range. The resulting measurements and predictions are of sufficient coverage to adequately address astrophysical questions about this species using the Herschel Space Observatory or the Atacama Large Millimeter Array
Rotational spectroscopy of the HCCO and DCCO radicals in the millimeter and submillimeter range
The ketenyl radical, HCCO, has recently been detected in the ISM for the
first time. Further astronomical detections of HCCO will help us understand its
gas-grain chemistry, and subsequently revise the oxygen-bearing chemistry
towards dark clouds. Moreover, its deuterated counterpart, DCCO, has never been
observed in the ISM. HCCO and DCCO still lack a broad spectroscopic
investigation, although they exhibit a significant astrophysical relevance. In
this work we aim to measure the pure rotational spectra of the ground state of
HCCO and DCCO in the millimeter and submillimeter region, considerably
extending the frequency range covered by previous studies. The spectral
acquisition was performed using a frequency-modulation absorption spectrometer
between 170 and 650 GHz. The radicals were produced in a low-density plasma
generated from a select mixture of gaseous precursors. For each isotopologue we
were able to detect and assign more than 100 rotational lines. The new lines
have significantly enhanced the previous data set allowing the determination of
highly precise rotational and centrifugal distortion parameters. In our
analysis we have taken into account the interaction between the ground
electronic state and a low-lying excited state (Renner-Teller pair) which
enables the prediction and assignment of rotational transitions with up
to 4. The present set of spectroscopic parameters provides highly accurate,
millimeter and submillimeter rest-frequencies of HCCO and DCCO for future
astronomical observations. We also show that towards the pre-stellar core
L1544, ketenyl peaks in the region where - peaks,
suggesting that HCCO follows a predominant hydrocarbon chemistry, as already
proposed by recent gas-grain chemical models
Conformations of confined biopolymers
Nanoscale and microscale confinement of biopolymers naturally occurs in cells
and has been recently achieved in artificial structures designed for
nanotechnological applications. Here, we present an extensive theoretical
investigation of the conformations and shape of a biopolymer with varying
stiffness confined to a narrow channel. Combining scaling arguments, analytical
calculations, and Monte Carlo simulations, we identify various scaling regimes
where master curves quantify the functional dependence of the polymer
conformations on the chain stiffness and strength of confinement.Comment: 5 pages, 4 figures, minor correction
Fluctuation-Dissipation Theorem for the Microcanonical Ensemble
A derivation of the Fluctuation-Dissipation Theorem for the microcanonical
ensemble is presented using linear response theory. The theorem is stated as a
relation between the frequency spectra of the symmetric correlation and
response functions. When the system is not in the thermodinamic limit, this
result can be viewed as an extension of the fluctuation-dissipation relations
to a situation where dynamical fluctuations determine the response. Therefore,
the relation presented here between equilibrium fluctuations and response can
have a very different physical nature from the usual one in the canonical
ensemble. These considerations imply that the Fluctuation-Dissipation Theorem
is not restricted to the context of thermal equilibrium, where it is usually
derived. Dispersion relations and sum rules are also obtained and discussed in
the present case. Although analogous to the Kramers-Kronig relations, they are
not related to the frequency spectrum but to the energy dependence of the
response function.Comment: 15 pages, v3: final version, new text added, new reference
Signatures of clumpy dark matter in the global 21 cm background signal
We examine the extent to which the self-annihilation of supersymmetric
neutralino dark matter, as well as light dark matter, influences the rate of
heating, ionisation and Lyman-alpha pumping of interstellar hydrogen and helium
and the extent to which this is manifested in the 21cm global background
signal. We fully consider the enhancements to the annihilation rate from DM
halos and substructures within them. We find that the influence of such
structures can result in significant changes in the differential brightness
temperature. The changes at redsfhits z<25 are likely to be undetectable due to
the presence of the astrophysical signal; however, in the most favourable
cases, deviations in the differential brightness temperature, relative to its
value in the absence of self-annihilating DM, of up to ~20 mK at z=30 can
occur. Thus we conclude that, in order to exclude these models, experiments
measuring the global 21cm signal, such as EDGES and CORE, will need to reduce
the systematics at 50 MHz to below 20 mK.Comment: V3: 32 pages, 14 figures, 4 tables. Replaced to match version
accepted for publication in PRD. Major revisions to address referee's
comment
Lessons from the Congested Clique Applied to MapReduce
The main results of this paper are (I) a simulation algorithm which, under
quite general constraints, transforms algorithms running on the Congested
Clique into algorithms running in the MapReduce model, and (II) a distributed
-coloring algorithm running on the Congested Clique which has an
expected running time of (i) rounds, if ;
and (ii) rounds otherwise. Applying the simulation theorem to
the Congested-Clique -coloring algorithm yields an -round
-coloring algorithm in the MapReduce model.
Our simulation algorithm illustrates a natural correspondence between
per-node bandwidth in the Congested Clique model and memory per machine in the
MapReduce model. In the Congested Clique (and more generally, any network in
the model), the major impediment to constructing fast
algorithms is the restriction on message sizes. Similarly, in the
MapReduce model, the combined restrictions on memory per machine and total
system memory have a dominant effect on algorithm design. In showing a fairly
general simulation algorithm, we highlight the similarities and differences
between these models.Comment: 15 page
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