12,042 research outputs found
Half Cycle Pulse Train Induced State Redistribution of Rydberg Atoms
Population transfer between low lying Rydberg states independent of the
initial state is realized using a train of half-cycle pulses with pulse
durations much less than the classical orbit period. We demonstrate
experimentally the transfer of population from initial states around n=50 down
to n<40 as well as up to the continuum. The measured population transfer
matches well to a model of the process for 1D atoms.Comment: V2: discussion extended, version accepted for publication in Physical
Review
RVB gauge theory and the Topological degeneracy in the Honeycomb Kitaev model
We relate the Z gauge theory formalism of the Kitaev model to the SU(2)
gauge theory of the resonating valence bond (RVB) physics. Further, we
reformulate a known Jordan-Wigner transformation of Kitaev model on a torus in
a general way that shows that it can be thought of as a Z gauge fixing
procedure. The conserved quantities simplify in terms of the gauge invariant
Jordan-Wigner fermions, enabling us to construct exact eigen states and
calculate physical quantities. We calculate the fermionic spectrum for flux
free sector for different gauge field configurations and show that the ground
state is four-fold degenerate on a torus in thermodynamic limit. Further on a
torus we construct four mutually anti-commuting operators which enable us to
prove that all eigenstates of this model are four fold degenerate in
thermodynamic limit.Comment: 12 pages, 3 figures. Added affiliation and a new section,
'Acknowledgements'.Typos correcte
Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure
Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key
factors for the free layer magnetization switching by spin transfer torque
technique in magnetic tunnel junction devices. The magnetization precessional
dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure
was explored in broad band frequency range by employing micro-strip
ferromagnetic resonance technique. The polar angular variation of resonance
field and linewidth at different frequencies have been analyzed numerically
using Landau-Lifshitz-Gilbert equation by taking into account the total free
energy density of the film. The numerically estimated parameters Land\'{e}
-factor, PMA constant, and effective magnetization are found to be 2.1,
2 erg/cm and 7145 Oe, respectively. The frequency
dependence of Gilbert damping parameter () is evaluated by considering
both intrinsic and extrinsic effects into the total linewidth analysis. The
value of is found to be 0.006 at 10 GHz and it increases with
decreasing precessional frequency.Comment: 5 Pages, 6 Figures, Regular Submissio
Rolling tachyon solution of two-dimensional string theory
We consider a classical (string) field theory of matrix model which was
developed earlier in hep-th/9207011 and subsequent papers. This is a
noncommutative field theory where the noncommutativity parameter is the string
coupling . We construct a classical solution of this field theory and show
that it describes the complete time history of the recently found rolling
tachyon on an unstable D0 brane.Comment: 19 pages, 2 figures, minor changes in text and additional references,
correction of decay time (version to appear in JHEP.
A personalised medicine approach for ponatinib-resistant chronic myeloid leukaemia.
BACKGROUND: Chronic myeloid leukaemia (CML) is characterised by the presence of a fusion driver oncogene, BCR-ABL1, which is a constitutive tyrosine kinase. Tyrosine kinase inhibitors (TKIs) are the central treatment strategy for CML patients and have significantly improved survival rates, but the T315I mutation in the kinase domain of BCR-ABL1 confers resistance to all clinically approved TKIs, except ponatinib. However, compound mutations can mediate resistance even to ponatinib and remain a clinical challenge in CML therapy. Here, we investigated a ponatinib-resistant CML patient through whole-genome sequencing (WGS) to identify the cause of resistance and to find alternative therapeutic targets. PATIENTS AND METHODS: We carried out WGS on a ponatinib-resistant CML patient and demonstrated an effective combination therapy against the primary CML cells derived from this patient in vitro. RESULTS: Our findings demonstrate the emergence of compound mutations in the BCR-ABL1 kinase domain following ponatinib treatment, and chromosomal structural variation data predicted amplification of BCL2. The primary CD34(+) CML cells from this patient showed increased sensitivity to the combination of ponatinib and ABT-263, a BCL2 inhibitor with a negligible effect against the normal CD34(+) cells. CONCLUSION: Our results show the potential of personalised medicine approaches in TKI-resistant CML patients and provide a strategy that could improve clinical outcomes for these patients
Observation of a superconducting glass state in granular superconducting diamond
The magnetic field dependence of the superconductivity in nanocrystalline
boron doped diamond thin films is reported. Evidence of a glass state in the
phase diagram is presented, as demonstrated by electrical resistance and
magnetic relaxation measurements. The position of the phase boundary in the H-T
plane is determined from resistance data by detailed fitting to
zero-dimensional fluctuation conductivity theory. This allows determination of
the boundary between resistive and non-resistive behavior to be made with
greater precision than the standard ad hoc onset/midpoint/offset criterion
Fluctuation spectroscopy as a probe of granular superconducting diamond films
We present resistance versus temperature data for a series of boron-doped
nanocrystalline diamond films whose grain size is varied by changing the film
thickness. Upon extracting the fluctuation conductivity near to the critical
temperature we observe three distinct scaling regions -- 3D intragrain,
quasi-0D, and 3D intergrain -- in confirmation of the prediction of Lerner,
Varlamov and Vinokur. The location of the dimensional crossovers between these
scaling regions allows us to determine the tunnelling energy and the Thouless
energy for each film. This is a demonstration of the use of \emph{fluctuation
spectroscopy} to determine the properties of a superconducting granular system
Exact results for spin dynamics and fractionization in the Kitaev Model
We present certain exact analytical results for dynamical spin correlation
functions in the Kitaev Model. It is the first result of its kind in
non-trivial quantum spin models. The result is also novel: in spite of presence
of gapless propagating Majorana fermion excitations, dynamical two spin
correlation functions are identically zero beyond nearest neighbor separation,
showing existence of a gapless but short range spin liquid. An unusual,
\emph{all energy scale fractionization}of a spin -flip quanta, into two
infinitely massive -fluxes and a dynamical Majorana fermion, is shown to
occur. As the Kitaev Model exemplifies topological quantum computation, our
result presents new insights into qubit dynamics and generation of topological
excitations.Comment: 4 pages, 2 figures. Typose corrected, figure made better, clarifying
statements and references adde
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