1,191 research outputs found
Mean first passage time for nuclear fission and the emission of light particles
The concept of a mean first passage time is used to study the time lapse over
which a fissioning system may emit light particles. The influence of the
"transient" and "saddle to scission times" on this emission are critically
examined. It is argued that within the limits of Kramers' picture of fission no
enhancement over that given by his rate formula need to be considered.Comment: 4 pages, RevTex, 4 postscript figures; with correction of misprints;
appeared in Phys. Rev. Lett.90.13270
Coherent Population Trapping of Single Spins in Diamond Under Optical Excitation
Coherent population trapping is demonstrated in single nitrogen-vacancy
centers in diamond under optical excitation. For sufficient excitation power,
the fluorescence intensity drops almost to the background level when the laser
modulation frequency matches the 2.88 GHz splitting of the ground states. The
results are well described theoretically by a four-level model, allowing the
relative transition strengths to be determined for individual centers. The
results show that all-optical control of single spins is possible in diamond.Comment: minor correction
Quantitative test of the barrier nucleosome model for statistical positioning of nucleosomes up- and downstream of transcription start sites
The positions of nucleosomes in eukaryotic genomes determine which parts of
the DNA sequence are readily accessible for regulatory proteins and which are
not. Genome-wide maps of nucleosome positions have revealed a salient pattern
around transcription start sites, involving a nucleosome-free region (NFR)
flanked by a pronounced periodic pattern in the average nucleosome density.
While the periodic pattern clearly reflects well-positioned nucleosomes, the
positioning mechanism is less clear. A recent experimental study by Mavrich et
al. argued that the pattern observed in S. cerevisiae is qualitatively
consistent with a `barrier nucleosome model', in which the oscillatory pattern
is created by the statistical positioning mechanism of Kornberg and Stryer. On
the other hand, there is clear evidence for intrinsic sequence preferences of
nucleosomes, and it is unclear to what extent these sequence preferences affect
the observed pattern. To test the barrier nucleosome model, we quantitatively
analyze yeast nucleosome positioning data both up- and downstream from NFRs.
Our analysis is based on the Tonks model of statistical physics which
quantifies the interplay between the excluded-volume interaction of nucleosomes
and their positional entropy. We find that although the typical patterns on the
two sides of the NFR are different, they are both quantitatively described by
the same physical model, with the same parameters, but different boundary
conditions. The inferred boundary conditions suggest that the first nucleosome
downstream from the NFR (the +1 nucleosome) is typically directly positioned
while the first nucleosome upstream is statistically positioned via a
nucleosome-repelling DNA region. These boundary conditions, which can be
locally encoded into the genome sequence, significantly shape the statistical
distribution of nucleosomes over a range of up to ~1000 bp to each side.Comment: includes supporting materia
Numerical results for the exact spectrum of planar AdS4/CFT3
We compute the anomalous dimension for a short single-trace operator in
planar ABJM theory at intermediate coupling. This is done by solving
numerically the set of Thermodynamic Bethe Ansatz equations which are expected
to describe the exact spectrum of the theory. We implement a truncation method
which significantly reduces the number of integral equations to be solved and
improves numerical efficiency. Results are obtained for a range of 't Hooft
coupling lambda corresponding to , where h(lambda) is
the interpolating function of the AdS4/CFT3 Bethe equations.Comment: v3: corrected Acknowledgements section; v4: minor changes, published
version; v5: fixed typos in Eq. (3.9
Sensing remote nuclear spins
Sensing single nuclear spins is a central challenge in magnetic resonance
based imaging techniques. Although different methods and especially diamond
defect based sensing and imaging techniques in principle have shown sufficient
sensitivity, signals from single nuclear spins are usually too weak to be
distinguished from background noise. Here, we present the detection and
identification of remote single C-13 nuclear spins embedded in nuclear spin
baths surrounding a single electron spins of a nitrogen-vacancy centre in
diamond. With dynamical decoupling control of the centre electron spin, the
weak magnetic field ~10 nT from a single nuclear spin located ~3 nm from the
centre with hyperfine coupling as weak as ~500 Hz is amplified and detected.
The quantum nature of the coupling is confirmed and precise position and the
vector components of the nuclear field are determined. Given the distance over
which nuclear magnetic fields can be detected the technique marks a firm step
towards imaging, detecting and controlling nuclear spin species external to the
diamond sensor
Observation of discrete time-crystalline order in a disordered dipolar many-body system
Understanding quantum dynamics away from equilibrium is an outstanding
challenge in the modern physical sciences. It is well known that
out-of-equilibrium systems can display a rich array of phenomena, ranging from
self-organized synchronization to dynamical phase transitions. More recently,
advances in the controlled manipulation of isolated many-body systems have
enabled detailed studies of non-equilibrium phases in strongly interacting
quantum matter. As a particularly striking example, the interplay of periodic
driving, disorder, and strong interactions has recently been predicted to
result in exotic "time-crystalline" phases, which spontaneously break the
discrete time-translation symmetry of the underlying drive. Here, we report the
experimental observation of such discrete time-crystalline order in a driven,
disordered ensemble of dipolar spin impurities in diamond at
room-temperature. We observe long-lived temporal correlations at integer
multiples of the fundamental driving period, experimentally identify the phase
boundary and find that the temporal order is protected by strong interactions;
this order is remarkably stable against perturbations, even in the presence of
slow thermalization. Our work opens the door to exploring dynamical phases of
matter and controlling interacting, disordered many-body systems.Comment: 6 + 3 pages, 4 figure
Electrophysiological and behavioral properties of 4-aminopyridine-induced epileptic activity in mice
Quark--anti-quark potential in N=4 SYM
We construct a closed system of equations describing the quark--anti-quark
potential at any coupling in planar N=4 supersymmetric Yang-Mills theory. It is
based on the Quantum Spectral Curve method supplemented with a novel type of
asymptotics. We present a high precision numerical solution reproducing the
classical and one-loop string predictions very accurately. We also analytically
compute the first 7 nontrivial orders of the weak coupling expansion.
Moreover, we study analytically the generalized quark--anti-quark potential
in the limit of large imaginary twist to all orders in perturbation theory. We
demonstrate how the QSC reduces in this case to a one-dimensional Schrodinger
equation. In the process we establish a link between the Q-functions and the
solution of the Bethe-Salpeter equation.Comment: 31 pages, 1 figure; v2: minor correcton
Grand unified theory constrained supersymmetry and neutrinoless double beta decay
We analyze the contributions to the neutrinoless double decay
(-decay) coming from the Grand Unified Theory (GUT) constrained
Minimal Supersymmetric Standard Model (MSSM) with trilinear R-parity breaking.
We discuss the importance of two-nucleon and pion-exchange realizations of the
quark-level -decay transitions. In this context, the questions
of reliability of the calculated relevant nuclear matrix elements within the
Renormalized Quasiparticle Random Phase Approximation (pn-RQRPA) for several
medium and heavy open-shell nuclei are addressed. The importance of gluino and
neutralino contributions to -decay is also analyzed. We review
the present experiments and deduce limits on the trilinear R-parity breaking
parameter from the non-observability of -decay
for different GUT constrained SUSY scenarios. In addition, a detailed study of
limits on the MSSM parameter space coming from the processes
by using the recent CLEO and OPAL results is performed. Some studies in respect
to the future -decay project GENIUS are also presented.Comment: 29 pages, 8 figure
Quantum Spectral Curve at Work: From Small Spin to Strong Coupling in N=4 SYM
We apply the recently proposed quantum spectral curve technique to the study
of twist operators in planar N=4 SYM theory. We focus on the small spin
expansion of anomalous dimensions in the sl(2) sector and compute its first two
orders exactly for any value of the 't Hooft coupling. At leading order in the
spin S we reproduced Basso's slope function. The next term of order S^2
structurally resembles the Beisert-Eden-Staudacher dressing phase and takes
into account wrapping contributions. This expansion contains rich information
about the spectrum of local operators at strong coupling. In particular, we
found a new coefficient in the strong coupling expansion of the Konishi
operator dimension and confirmed several previously known terms. We also
obtained several new orders of the strong coupling expansion of the BFKL
pomeron intercept. As a by-product we formulated a prescription for the correct
analytical continuation in S which opens a way for deriving the BFKL regime of
twist two anomalous dimensions from AdS/CFT integrability.Comment: 53 pages, references added; v3: due to a typo in the coefficients C_2
and D_2 on page 29 we corrected the rational part of the strong coupling
predictions in equations (1.5-6), (6.22-24), (6.27-30) and in Table
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