45,023 research outputs found
Proposed New Test of Spin Effects in General Relativity
The recent discovery of a double-pulsar PSR J0737-3039A/B provides an
opportunity of unequivocally observing, for the first time, spin effects in
general relativity. Existing efforts involve detection of the precession of the
spinning body itself. However, for a close binary system, spin effects on the
orbit may also be discernable. Not only do they add to the advance of the
periastron (by an amount which is small compared to the conventional
contribution) but they also give rise to a precession of the orbit about the
spin direction. The measurement of such an effect would also give information
on the moment of inertia of pulsars
Roles of the Bloom's syndrome helicase in the maintenance of genome stability
The RecQ family of DNA helicases is highly conserved in evolution from bacteria to humans. Of the five known human RecQ family members, three (BLM, WRN and RECQ4, which cause Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome respectively) are mutated in distinct clinical disorders associated with cancer predisposition and/or premature aging. BLM forms part of a multienzyme complex including topoisomerase IIIalpha, replication protein A and a newly identified factor called BLAP75. Together, these proteins play a role in the resolution of DNA structures that arise during the process of homologous recombination repair. In the absence of BLM, cells show genomic instability and a high incidence of sister-chromatid exchanges. In addition to a DNA structure-specific helicase activity, BLM also catalyses Holliday-junction branch migration and the annealing of complementary single-stranded DNA molecules
Supersolid Helium at High Pressure
We have measured the pressure dependence of the supersolid fraction by a
torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9
bar. The supersolid fraction in the low temperature limit increases from 0.6 %
at 25.6 bar near the melting boundary up to a maximum of 1.5% near 55 bar
before showing a monotonic decrease with pressure extrapolating to zero near
170 bar.Comment: 4 pages, 4 figure
Exploring the magnetic properties of the largest single molecule magnets
The giant {Mn₇₀} and {Mn₈₄} wheels are the largest nuclearity single-molecule magnets synthesized to date, and understanding their magnetic properties poses a challenge to theory. Starting from first-principles calculations, we explore the magnetic properties and excitations in these wheels using effective spin Hamiltonians. We find that the unusual geometry of the superexchange pathways leads to weakly coupled {Mn₇} subunits carrying an effective S = 2 spin. The spectrum exhibits a hierarchy of energy scales and massive degeneracies, with the lowest-energy excitations arising from Heisenberg-ring-like excitations of the {Mn₇} subunits around the wheel. We further describe how weak longer-range couplings can select the precise spin ground-state of the Mn wheels out of the nearly degenerate ground-state band
Conditional preparation of states containing a definite number of photons
A technique for conditionally creating single- or multimode photon-number
states is analyzed using Bayesian theory. We consider the heralded N-photon
states created from the photons produced by an unseeded optical parametric
amplifier when the heralding detector is the time-multiplexed
photon-number-resolving detector recently demonstrated by Fitch, et al. [Phys.
Rev. A 68, 043814 (2003).] and simultaneously by Achilles, et al. [Opt. Lett.
28, 2387 (2003).]. We find that even with significant loss in the heralding
detector, fields with sub-Poissonian photon-number distributions can be
created. We also show that heralded multimode fields created using this
technique are more robust against detector loss than are single-mode fields.Comment: 6 pages, 6 figures, reference added, typos corrected, content update
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