879 research outputs found
Infinite Infrared Regularization and a State Space for the Heisenberg Algebra
We present a method for the construction of a Krein space completion for
spaces of test functions, equipped with an indefinite inner product induced by
a kernel which is more singular than a distribution of finite order. This
generalizes a regularization method for infrared singularities in quantum field
theory, introduced by G. Morchio and F. Strocchi, to the case of singularites
of infinite order. We give conditions for the possibility of this procedure in
terms of local differential operators and the Gelfand- Shilov test function
spaces, as well as an abstract sufficient condition. As a model case we
construct a maximally positive definite state space for the Heisenberg algebra
in the presence of an infinite infrared singularity.Comment: 18 pages, typos corrected, journal-ref added, reference adde
On the discrete spectrum of spin-orbit Hamiltonians with singular interactions
We give a variational proof of the existence of infinitely many bound states
below the continuous spectrum for spin-orbit Hamiltonians (including the Rashba
and Dresselhaus cases) perturbed by measure potentials thus extending the
results of J.Bruening, V.Geyler, K.Pankrashkin: J. Phys. A 40 (2007)
F113--F117.Comment: 10 pages; to appear in Russian Journal of Mathematical Physics
(memorial volume in honor of Vladimir Geyler). Results improved in this
versio
Effect of external pressure on the magnetic properties of CoAsO ( = La, Pr, Sm): a SR study
We report on a detailed investigation of the itinerant ferromagnets LaCoAsO,
PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the
application of external hydrostatic pressures up to GPa. These
materials are shown to be magnetically hard in view of the weak dependence of
both critical temperatures and internal fields at the muon site on .
In the cases = La and Sm, the behaviour of the internal field is
substantially unaltered up to GPa. A much richer phenomenology is
detected in PrCoAsO instead, possibly associated with a strong dependence
of the statistical population of the two different crystallographic sites for
the muon. Surprisingly, results are notably different from what is observed in
the case of the isostructural compounds CoPO, where the full As/P
substitution is already inducing a strong chemical pressure within the lattice
but is still very effective in further affecting the magnetic properties.Comment: 8 pages, 9 figure
CeRuSn: heavy fermions emerging from a Kondo-insulating state
The combination of low-temperature specific-heat and
nuclear-magnetic-resonance (NMR) measurements reveals important information of
the ground-state properties of CeRuSn, which has been proposed as a
rare example of a tetragonal Kondo-insulator (KI). The NMR
spin-latticerelaxation rate deviates from the Korringa law below 100 K
signaling the onset of an energy gap K. This gap is
stable against magnetic fields up to 10 T. Below 10 K, however, unusual
low-energy excitations of in-gap states are observed, which depend strongly on
the field H. The specific heat C detects these excitations in the form of an
enhanced Sommerfeld coefficient : In zero field,
increases steeply below 5 K, reaching a maximum at 0.1 K, and then saturates at
J/molK. This maximum is shifted to higher temperatures with
increasing field suggesting a residual density of states at the Fermi level
developing a spin gap . A simple model, based on two narrow
quasiparticle bands located at the Fermi level - which cross the Fermi level in
zero field at 0.022 states/meV f.u. - can account qualitatively as well as
quantitatively for the measured observables. In particular, it is demonstrated
that fitting our data of both specific heat and NMR to the model, incorporating
a Ce magnetic moment of , leads to
the prediction of the field dependence of the gap. Our measurements rule out
the presence of a quantum critical point as the origin for the enhanced
in CeRuSn and suggest that this arises rather from correlated,
residual in-gap states at the Fermi level. This work provides a fundamental
route for future investigations into the phenomenon of narrow-gap formation in
the strongly correlated class of systemComment: 11 pages, 13 figure
Spin Gap in the Single Spin-1/2 Chain Cuprate SrCaCuO
We report Cu nuclear magnetic resonance and muon spin rotation
measurements on the S=1/2 antiferromagnetic Heisenberg spin chain compound
SrCaCuO. An exponentially decreasing spin-lattice
relaxation rate 1/T indicates the opening of a spin gap. This behavior is
very similar to what has been observed for the cognate zigzag spin chain
compound SrCaCuO, and confirms that the occurrence of a
spin gap upon Ca doping is independent of the interchain exchange coupling
. Our results therefore generally prove the appearance of a spin gap in an
antiferromagnetic Heisenberg spin chain induced by a local bond disorder of the
intrachain exchange coupling . A low temperature upturn of 1/T evidences
growing magnetic correlations. However, zero field muon spin rotation
measurements down to 1.5 K confirm the absence of magnetic order in this
compound which is most likely suppressed by the opening of the spin gap.Comment: 5 pages, 4 figure
Toward a noncytotoxic glioblastoma therapy: blocking MCP-1 with the MTZ Regimen
To improve the prognosis of glioblastoma, we developed an adjuvant treatment directed to a neglected aspect of glioblastoma growth, the contribution of nonmalignant monocyte lineage cells (MLCs) (monocyte, macrophage, microglia, dendritic cells) that infiltrated a main tumor mass. These nonmalignant cells contribute to glioblastoma growth and tumor homeostasis. MLCs comprise of approximately 10%-30% of glioblastoma by volume. After integration into the tumor mass, these become polarized toward an M2 immunosuppressive, pro-angiogenic phenotype that promotes continued tumor growth. Glioblastoma cells initiate and promote this process by synthesizing 13 kDa MCP-1 that attracts circulating monocytes to the tumor. Infiltrating monocytes, after polarizing toward an M2 phenotype, synthesize more MCP-1, forming an amplification loop. Three noncytotoxic drugs, an antibiotic - minocycline, an antihypertensive drug - telmisartan, and a bisphosphonate - zoledronic acid, have ancillary attributes of MCP-1 synthesis inhibition and could be re-purposed, singly or in combination, to inhibit or reverse MLC-mediated immunosuppression, angiogenesis, and other growth-enhancing aspects. Minocycline, telmisartan, and zoledronic acid - the MTZ Regimen - have low-toxicity profiles and could be added to standard radiotherapy and temozolomide. Re-purposing older drugs has advantages of established safety and low drug cost. Four core observations support this approach: 1) malignant glioblastoma cells require a reciprocal trophic relationship with nonmalignant macrophages or microglia to thrive;2) glioblastoma cells secrete MCP-1 to start the cycle, attracting MLCs, which subsequently also secrete MCP-1 perpetuating the recruitment cycle;3) increasing cytokine levels in the tumor environment generate further immunosuppression and tumor growth;and 4) MTZ regimen may impede MCP-1-driven processes, thereby interfering with glioblastoma growth
Parametrizations of density matrices
This article gives a brief overview of some recent progress in the
characterization and parametrization of density matrices of finite dimensional
systems. We discuss in some detail the Bloch-vector and Jarlskog
parametrizations and mention briefly the coset parametrization. As applications
of the Bloch parametrization we discuss the trace invariants for the case of
time dependent Hamiltonians and in some detail the dynamics of three-level
systems. Furthermore, the Bloch vector of two-qubit systems as well as the use
of the polarization operator basis is indicated. As the main application of the
Jarlskog parametrization we construct density matrices for composite systems.
In addition, some recent related articles are mentioned without further
discussion.Comment: 31 pages. v2: 32 pages, Abstract and Introduction rewritten and
Conclusion section added, references adde
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