6,989 research outputs found
Discovery of carbon monoxide in the upper atmosphere of Pluto
Pluto's icy surface has changed colour and its atmosphere has swelled since
its last closest approach to the Sun in 1989. The thin atmosphere is produced
by evaporating ices, and so can also change rapidly, and in particular carbon
monoxide should be present as an active thermostat. Here we report the
discovery of gaseous CO via the 1.3mm wavelength J=2-1 rotational transition,
and find that the line-centre signal is more than twice as bright as a
tentative result obtained by Bockelee-Morvan et al. in 2000. Greater
surface-ice evaporation over the last decade could explain this, or increased
pressure could have caused the atmosphere to expand. The gas must be cold, with
a narrow line-width consistent with temperatures around 50 K, as predicted for
the very high atmosphere, and the line brightness implies that CO molecules
extend up to approximately 3 Pluto radii above the surface. The upper
atmosphere must have changed markedly over only a decade since the prior
search, and more alterations could occur by the arrival of the New Horizons
mission in 2015.Comment: 5 pages; accepted for publication in MNRAS Letter
UCN Upscattering rates in a molecular deuterium crystal
A calculation of ultra-cold neutron (UCN) upscattering rates in molecular
deuterium solids has been carried out, taking into account intra-molecular
exictations and phonons. The different moelcular species ortho-D2 (with even
rotational quantum number J) and para-D2 (with odd J) exhibit significantly
different UCN-phonon annihilation cross-sections. Para- to ortho-D2 conversion,
furthermore, couples UCN to an energy bath of excited rotational states without
mediating phonons. This anomalous upscattering mechanism restricts the UCN
lifetime to 4.6 msec in a normal-D2 solid with 33% para content.Comment: 3 pages, one figur
Technical note: successful DNA amplification of DNA from non-destructive buccal swabbing in Vespertilionid and Rhinolophid bats
\ua9 The Author(s) 2024.Acquiring DNA from wild bats (Mammalia: Chiroptera) is typically undertaken utilizing highly invasive (but non-lethal) sampling techniques comprising wing biopsies and occasional blood samples. While non-invasive sampling is possible through the extraction of DNA from faecal samples, it is not always possible to acquire samples from individual bats whilst conducting fieldwork, and as such, this method is primarily applicable to roost occupancy identification. Similarly, wing swabbing is liable to cross-contamination from roost mates. Here we present the first use of oral (buccal) swabbing for successful, species-resolution DNA sequencing of Vespertilionidae and Rhinolophidae in 10 bat species (nine Vespertilionidae and one Rhinolophidae) from the UK
Incommensurate Charge and Spin Fluctuations in d-wave Superconductors
We show analytic results for the irreducible charge and spin
susceptibilities, , where is the momentum
transfer between the nodes in d-wave superconductors. Using the BCS theory and
a circular Fermi surface, we find that the singular behavior of the irreducible
charge susceptibility leads to the dynamic incommensurate charge collective
modes. The peaks in the charge structure factor occur at a set of wave vectors
which form an ellipse around and in
momentum space with momentum dependent spectral weight. It is also found that,
due to the non-singular irreducible spin susceptibility, an extremely strong
interaction via random phase approximation is required to support the magnetic
peaks near . Under certain conditions, the peaks in the magnetic
structure factor occur near and .Comment: 5 pages, 3 figure
Atom interferometer as a selective sensor of rotation or gravity
In the presence of Earth gravity and gravity-gradient forces, centrifugal and
Coriolis forces caused by the Earth rotation, the phase of the time-domain atom
interferometers is calculated with accuracy up to the terms proportional to the
fourth degree of the time separation between pulses. We considered double-loop
atom interferometers and found appropriate condition to eliminate their
sensitivity to acceleration to get atomic gyroscope, or to eliminate the
sensitivity to rotation to increase accuracy of the atomic gravimeter.
Consequent use of these interferometers allows one to measure all components of
the acceleration and rotation frequency projection on the plane perpendicular
to gravity acceleration. Atom interference on the Raman transition driving by
noncounterpropagating optical fields is proposed to exclude stimulated echo
processes which can affect the accuracy of the atomic gyroscopes. Using
noncounterpropagating optical fields allows one to get a new type of the Ramsey
fringes arising in the unidirectional Raman pulses and therefore centered at
the two-quantum line center. Density matrix in the Wigner representation is
used to perform calculations. It is shown that in the time between pulses, in
the noninertial frame, for atoms with fully quantized spatial degrees of
freedom, this density matrix obeys classical Liouville equations.Comment: 21 pages, 4 figures, extended references, discussion, and motivatio
Development of a generic activities model of command and control
This paper reports on five different models of command and control. Four different models are reviewed: a process model, a contextual control model, a decision ladder model and a functional model. Further to this, command and control activities are analysed in three distinct domains: armed forces, emergency services and civilian services. From this analysis, taxonomies of command and control activities are developed that give rise to an activities model of command and control. This model will be used to guide further research into technological support of command and control activities
Symmetry, complexity and multicritical point of the two-dimensional spin glass
We analyze models of spin glasses on the two-dimensional square lattice by
exploiting symmetry arguments. The replicated partition functions of the Ising
and related spin glasses are shown to have many remarkable symmetry properties
as functions of the edge Boltzmann factors. It is shown that the applications
of homogeneous and Hadamard inverses to the edge Boltzmann matrix indicate
reduced complexities when the elements of the matrix satisfy certain
conditions, suggesting that the system has special simplicities under such
conditions. Using these duality and symmetry arguments we present a conjecture
on the exact location of the multicritical point in the phase diagram.Comment: 32 pages, 6 figures; a few typos corrected. To be published in J.
Phys.
The optical calcium frequency standards of PTB and NIST
We describe the current status of the Ca optical frequency standards with
laser-cooled neutral atoms realized in two different laboratories for the
purpose of developing a possible future optical atomic clock.
Frequency measurements performed at the Physikalisch-Technische Bundesanstalt
(PTB) and the National Institute of Standards and Technology (NIST) make the
frequency of the clock transition of 40Ca one of the best known optical
frequencies (relative uncertainty 1.2e-14) and the measurements of this
frequency in both laboratories agree to well within their respective
uncertainties.
Prospects for improvement by orders of magnitude in the relative uncertainty
of the standard look feasible.Comment: 13 pages, 11 figures, to appear in Comptes Rendus Physiqu
Screening and classifying small-molecule inhibitors of amyloid formation using ion mobility spectrometry-mass spectrometry
The search for therapeutic agents that bind specifically to precursor protein conformations and inhibit amyloid assembly is an important challenge. Identifying such inhibitors is difficult because many protein precursors of aggregation are partially folded or intrinsically disordered, which rules out structure-based design. Furthermore, inhibitors can act by a variety of mechanisms, including specific or nonspecific binding, as well as colloidal inhibition. Here we report a high-throughput method based on ion mobility spectrometry–mass spectrometry (IMS–MS) that is capable of rapidly detecting small molecules that bind to amyloid precursors, identifying the interacting protein species and defining the mode of inhibition. Using this method we have classified a variety of small molecules that are potential inhibitors of human ​islet amyloid polypeptide (​hIAPP) aggregation or ​amyloid-beta 1-40 aggregation as specific, nonspecific, colloidal or non-interacting. We also demonstrate the ability of IMS–MS to screen for inhibitory small molecules in a 96-well plate format and use this to discover a new inhibitor of ​hIAPP amyloid assembly
Sub-dekahertz ultraviolet spectroscopy of 199Hg+
Using a laser that is frequency-locked to a Fabry-Perot etalon of high
finesse and stability, we probe the 5d10 6s 2S_1/2 (F=0) - 5d9 6s 2D_5/2 (F=2)
Delta-m_F = 0 electric-quadrupole transition of a single laser-cooled 199Hg+
ion stored in a cryogenic radio-frequency ion trap. We observe
Fourier-transform limited linewidths as narrow as 6.7 Hz at 282 nm (1.06 X
10^15 Hz), yielding a line Q = 1.6 X 10^14. We perform a preliminary
measurement of the 5d9 6s2 2D_5/2 electric-quadrupole shift due to interaction
with the static fields of the trap, and discuss the implications for future
trapped-ion optical frequency standards.Comment: 4 pages, 4 figures, submitted for publicatio
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