2,182 research outputs found
Site symmetry and crystal symmetry: a spherical tensor analysis
The relation between the properties of a specific crystallographic site and
the properties of the full crystal is discussed by using spherical tensors. The
concept of spherical tensors is introduced and the way it transforms under the
symmetry operations of the site and from site to site is described in detail.
The law of spherical tensor coupling is given and illustrated with the example
of the electric dipole and quadrupole transitions in x-ray absorption
spectroscopy. The main application of the formalism is the reduction of
computation time in the calculation of the properties of crystals by band
structure methods. The general approach is illustrated by the examples of
substitutional chromium in spinel and substitutional vanadium in garnet.Comment: 27 pages, 3 figure
Nuclear Clusters as a Probe for Expansion Flow in Heavy Ion Reactions at 10-15AGeV
A phase space coalescence description based on the Wigner-function method for
cluster formation in relativistic nucleus-nucleus collisions is presented. The
momentum distributions of nuclear clusters d,t and He are predicted for central
Au(11.6AGeV)Au and Si(14.6AGeV)Si reactions in the framework of the RQMD
transport approach. Transverse expansion leads to a strong shoulder-arm shape
and different inverse slope parameters in the transverse spectra of nuclear
clusters deviating markedly from thermal distributions. A clear ``bounce-off''
event shape is seen: the averaged transverse flow velocities in the reaction
plane are for clusters larger than for protons. The cluster yields
--particularly at low at midrapidities-- and the in-plane (anti)flow of
clusters and pions change if suitably strong baryon potential interactions are
included. This allows to study the transient pressure at high density via the
event shape analysis of nucleons, nucleon clusters and other hadrons.Comment: 38 pages, 9 figures, LaTeX type, eps used, subm. to Phys. Rev.
Hedgehog pathway mutations drive oncogenic transformation in high-risk T-cell acute lymphoblastic leukemia.
The role of Hedgehog signaling in normal and malignant T-cell development is controversial. Recently, Hedgehog pathway mutations have been described in T-ALL, but whether mutational activation of Hedgehog signaling drives T-cell transformation is unknown, hindering the rationale for therapeutic intervention. Here, we show that Hedgehog pathway mutations predict chemotherapy resistance in human T-ALL, and drive oncogenic transformation in a zebrafish model of the disease. We found Hedgehog pathway mutations in 16% of 109 childhood T-ALL cases, most commonly affecting its negative regulator PTCH1. Hedgehog mutations were associated with resistance to induction chemotherapy (P = 0.009). Transduction of wild-type PTCH1 into PTCH1-mutant T-ALL cells induced apoptosis (P = 0.005), a phenotype that was reversed by downstream Hedgehog pathway activation (P = 0.007). Transduction of most mutant PTCH1, SUFU, and GLI alleles into mammalian cells induced aberrant regulation of Hedgehog signaling, indicating that these mutations are pathogenic. Using a CRISPR/Cas9 system for lineage-restricted gene disruption in transgenic zebrafish, we found that ptch1 mutations accelerated the onset of notch1-induced T-ALL (P = 0.0001), and pharmacologic Hedgehog pathway inhibition had therapeutic activity. Thus, Hedgehog-activating mutations are driver oncogenic alterations in high-risk T-ALL, providing a molecular rationale for targeted therapy in this disease
Towards Quantum Repeaters with Solid-State Qubits: Spin-Photon Entanglement Generation using Self-Assembled Quantum Dots
In this chapter we review the use of spins in optically-active InAs quantum
dots as the key physical building block for constructing a quantum repeater,
with a particular focus on recent results demonstrating entanglement between a
quantum memory (electron spin qubit) and a flying qubit (polarization- or
frequency-encoded photonic qubit). This is a first step towards demonstrating
entanglement between distant quantum memories (realized with quantum dots),
which in turn is a milestone in the roadmap for building a functional quantum
repeater. We also place this experimental work in context by providing an
overview of quantum repeaters, their potential uses, and the challenges in
implementing them.Comment: 51 pages. Expanded version of a chapter to appear in "Engineering the
Atom-Photon Interaction" (Springer-Verlag, 2015; eds. A. Predojevic and M. W.
Mitchell
Examining leptogenesis with lepton flavor violation and the dark matter abundance
Within a supersymmetric (SUSY) type-I seesaw framework with flavor-blind
universal boundary conditions, we study the consequences of requiring that the
observed baryon asymmetry of the Universe be explained by either thermal or
non-thermal leptogenesis. In the former case, we find that the parameter space
is very constrained. In the bulk and stop-coannihilation regions of mSUGRA
parameter space (that are consistent with the measured dark matter abundance),
lepton flavor-violating (LFV) processes are accessible at MEG and future
experiments. However, the very high reheat temperature of the Universe needed
after inflation (of about 10^{12} GeV) leads to a severe gravitino problem,
which disfavors either thermal leptogenesis or neutralino dark matter.
Non-thermal leptogenesis in the preheating phase from SUSY flat directions
relaxes the gravitino problem by lowering the required reheat temperature. The
baryon asymmetry can then be explained while preserving neutralino dark matter,
and for the bulk or stop-coannihilation regions LFV processes should be
observed in current or future experiments.Comment: 20 pages, 5 figures, 1 tabl
Moscow-type NN-potentials and three-nucleon bound states
A detailed description of Moscow-type (M-type) potential models for the NN
interaction is given. The microscopic foundation of these models, which appear
as a consequence of the composite quark structure of nucleons, is discussed.
M-type models are shown to arise naturally in a coupled channel approach when
compound or bag-like six-quark states, strongly coupled to the NN channel, are
eliminated from the complete multiquark wave function. The role of the
deep-lying bound states that appear in these models is elucidated. By
introducing additional conditions of orthogonality to these compound six-quark
states, a continuous series of almost on-shell equivalent nonlocal interaction
models, characterized by a strong reduction or full absence of a local
repulsive core (M-type models), is generated. The predictions of these
interaction models for 3N systems are analyzed in detail. It is shown that
M-type models give, under certain conditions, a stronger binding of the 3N
system than the original phase-equivalent model with nodeless wave functions.
An analysis of the 3N system with the new versions of the Moscow NN potential
describing also the higher even partial waves is presented. Large deviations
from conventional NN force models are found for the momentum distribution in
the high momentum region. In particular, the Coulomb displacement energy for
nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H
binding energy is extrapolated to the experimental value.Comment: 23 pages Latex, 9 figures, to appear in Phys.Rev.
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Multiparticle azimuthal correlations for extracting event-by-event elliptic and triangular flow in Au + Au collisions at sNN =200 GeV
We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity 1<|η|<3 in Au + Au collisions at sNN=200 GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients v2{2},v2{4},v2{6}, and v2{8}, and triangular flow coefficients v3{2} and v3{4}. Using the small-variance limit, we estimate the mean and variance of the event-by-event v2 distribution from v2{2} and v2{4}. In a complementary analysis, we also use a folding procedure to study the distributions of v2 and v3 directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final-state momentum distributions are discussed
Equity as a Prerequisite for Stability of Cooperation on Global Public Good Provision
Analysing cooperative provision of a global public good such as climate protection, we explore the relationship between equitable burden sharing on the one hand and core stability on the other. To assess the size of the burden which a public good contribution entails for a country, we make use of a specific measure based on Moulin (Econometrica 55:963-977, 1987). In particular, we show that a Pareto optimal allocation which is not in the core can always be blocked by a group of countries with the highest Moulin sacrifices. In this sense, it is the 'overburdening' and thus 'unfair' treatment of some countries that provides the reason for core instability. By contrast, a Pareto optimal allocation is in the core if the public good contributions are fairly equally distributed according to their Moulin sacrifices. The potential implications of our theoretical analysis for global climate policy are also discussed
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
Rare brain biopsy findings in a first ADEM-like event of pediatric MS: histopathologic, neuroradiologic and clinical features
Pediatric MS tends to present more often with an acute onset and a polysymptomatic form of the disease, possibly with encephalopathy and large tumefactive lesions similar to those observed in some cases of acute disseminated encephalomyelitis (ADEM), which makes it more difficult to differentiate between an explosive and severe onset of MS vs. ADEM. An ADEM-like first demyelinating event can be the first attack of pediatric MS, but international consensus definitions require two or more non-ADEM demyelinating events for diagnosis of MS. In our patient KIDMUS MRI criteria for MS (Mikaeloff et al. J Pediatr 144:246–252, 2004a; Mikaeloff et al. Brain 127:1942–1947, 2004b) were negative at first attack, but Barkhof criteria for lesion dissemination in space in adults (Barkhof et al. 120:2059–2069, 1997), Callen modified MS-criteria and Callen MS-ADEM criteria for children (Callen et al. Neurology 72:961–967, 2009a; Callen et al. Neurology 72:968–973, 2009b) were positive suggesting pediatric MS. As the clinical course was devastating with non-responsiveness upon high-dose immune modulatory therapy and due to the absence of an alternative diagnosis other than demyelinating disease brain biopsy was performed. Brain biopsy studies or autopsy case reports of fulminant pediatric MS patients are extremely rare. Histopathology revealed an inflammatory demyelinating CNS process with confluent demyelination, indicating the likelihood of a relapsing disease course compatible with an acute to subacute demyelinating inflammatory disease. This pattern was corresponding to the early active multiple sclerosis subtype I of Lucchinetti et al. (Ann Neurol 47(6):707–717, 2000)
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