81 research outputs found
D-branes and the Non-commutative Structure of Quantum Spacetime
A worldsheet approach to the study of non-abelian D-particle dynamics is
presented based on viewing matrix-valued D-brane coordinate fields as coupling
constants of a deformed sigma-model which defines a logarithmic conformal field
theory. The short-distance structure of spacetime is shown to be naturally
captured by the Zamolodchikov metric on the corresponding moduli space which
encodes the geometry of the string interactions between D-particles. Spacetime
quantization is induced directly by the string genus expansion and leads to new
forms of uncertainty relations which imply that general relativity at very
short-distance scales is intrinsically described by a non-commutative geometry.
The indeterminancies exhibit decoherence effects suggesting the natural
incorporation of quantum gravity by short-distance D-particle probes. Some
potential experimental tests are briefly described.Comment: 20 pages LaTeX, 3 eps figures, uses epsf.sty; Based on talks given by
R.J.S. at SUSY'98, Oxford, England, July 11-17, 1998, and by N.E.M. at the
6th Hellenic School and Workshop on Elementary Particle Physics, TMR project
"Physics Beyond the Standard Model", Corfu, Greece, September 15-18, 199
Matrix Sigma-models for Multi D-brane Dynamics
We describe a dynamical worldsheet origin for the Lagrangian describing the
low-energy dynamics of a system of parallel D-branes. We show how matrix-valued
collective coordinate fields for the D-branes naturally arise as couplings of a
worldsheet sigma-model, and that the quantum dynamics require that these
couplings be mutually noncommutative. We show that the low-energy effective
action for the sigma-model couplings describes the propagation of an open
string in the background of the multiple D-brane configuration, in which all
string interactions between the constituent branes are integrated out and the
genus expansion is taken into account, with a matrix-valued coupling. The
effective field theory is governed by the non-abelian Born-Infeld target space
action which leads to the standard one for D-brane field theory.Comment: 14 pages LaTeX, 1 encapsulated postscript figure; uses epsf.te
Gradient Flow in Logarithmic Conformal Field Theory
We establish conditions under which the worldsheet beta-functions of
logarithmic conformal field theories can be derived as the gradient of some
scalar function on the moduli space of running coupling constants. We derive a
renormalization group invariant version of this function and relate it to the
usual Zamolodchikov C-function expressed in terms of correlation functions of
the worldsheet energy-momentum tensor. The results are applied to the example
of D-brane recoil in string theory.Comment: 12 pages LaTeX; references updated, one added; to be published in
Physics Letters
Conditional stability parameters for the actinides (IV)-humic acid system: a search for consistency
http://www.radiochimacta.deInternational audienceThe coherence of actinide(IV) complexation by humic substances (HS) is reviewed and new data are proposed. In a first attempt, the values of independent data from literature on Th(IV), U(IV), and Pu(IV) are collected, selected, and compiled. The data obtained follow the “classical” trend of increasing conditional formation “constants” with pH, led both by the increasing ionisation of HS and by the extensive hydrolysis of the tetravalent actinides. Even though a fair agreement is evident, the experimental uncertainties do not permit a full analogy between the actinides(IV) to be ascertained. In a second attempt, the experiments from which the original data are available were reinterpreted using only one hydrolysis constant set for U(IV) as an example, considering that all actinides(IV) have analogous humic complexation behaviour. Hence, the obtained evolution of conditional formation “constants” is much more coherent and the uncertainties do not permit to distinguish an actinide(IV) from one another. The obtained data are then applied to independent laboratory and in situ experiments in order to delimit the domain of possible applicability. This exercise demonstrates the treatment of data through analogy in the case of actinides(IV) and would permit to limit and orientate the number of necessary, but difficult, experiment with redox sensitive elements like U, Np, or Pu. It also demonstrates that complexation-only mechanisms may not be sufficient to understand field observations
Phase-sensitive amplification of 11 WDM channels across bandwidth of 8 nm in a fibre optic parametric amplifier
We experimentally demonstrate phase-sensitive fibre optic parametric amplification with gain >10dB and optical noise figure below 3dB for 11 channels spaced of 100 GHz. We employ all-fibre dispersion management to achieve a wideband phase-matching between signals and their copies
Parametric Amplification and Wavelength Conversion in Dual-Core Highly Nonlinear Fibers
In this paper we experimentally show parametric amplification and wavelength conversion in a custom manufactured dual-core highly nonlinear fiber. On-off gain > 10 dB and conversion efficiencies between −1 and −8.5 dB were measured for both cores. The estimated effective nonlinear parameter for the cores of the fiber are 6.6 W−1.km−1 and 6.3 W−1.km−1, while the zero-dispersion wavelength for the individual cores is shown to be relatively close from each other. Furthermore, complementary analytical and numerical results show that coupled cores fiber optical parametric amplifier offer the potential of wide-band gain even when they have significantly distinct zero-dispersion wavelengths
Time Delays of Strings in D-particle Backgrounds and Vacuum Refractive Indices
Using standard techniques in string/D-brane scattering amplitude
computations, we evaluate the scattering of open strings off D-particles in
brane world scenarios. The D-particles are viewed as D3 branes wrapped up
around three cycles, and their embedding in brane worlds constitutes a case of
intersecting branes, among which strings are stretched, representing various
types of excitations of the Standard Model (SM) particles in the low-energy
limit. Our analysis, reveals interesting and novel selection rules for the
resulting causal time delays, proportional to the energy of the incident matter
state, from the processes of splitting, capture and re-emission of the latter
by the D-particles. In particular, we show that there are relatively large time
delays only for excitations that belong to the Cartan subalgebra of the SM
gauge group, which notably includes photons. We discuss the possible relevance
of these results to the models of space time foam predicting a non-trivial
vacuum refractive index for photons and the associated cosmic \gamma-ray
phenomenology. In particular, we demonstrate how low-string-scale models can be
falsified already in this context, by current astrophysical observations of
cosmic photons, and how such observations serve as a way to discriminate low-
from high-string scale models.Comment: RevTex4, 10 pages, 3 eps.figures incorporated, amended discussion on
Lorentz symmetry (section I), and on gamma-ray phenomenology, based on
version to appear in Phys. Lett.
Carfilzomib, thalidomide, and dexamethasone is safe and effective in relapsed and/or refractory multiple myeloma: final report of the single arm, multicenter phase II ALLG MM018/AMN002 study.
This multicentre, phase II study of the Australian Lymphoma and Leukaemia Group (ALLG) and the Asian Myeloma Network (AMN) investigated fixed-duration (18-month) treatment with carfilzomib (K), thalidomide (T), and dexamethasone (d; KTd) in patients with relapsed and/or refractory multiple myeloma and 1-3 prior lines of therapy. Patients received induction with up to twelve 28-day cycles of K [20mg/m2 IV cycle 1 day 1 and 2, 56mg/m2 (36mg/m2 for patients ≥75 years) from day 8 onwards), T 100mg PO nocte and weekly dexamethasone 40mg (20mg for patients ≥75 years). During maintenance T was omitted, while K continued on days 1,2,15,16 with fortnightly dexamethasone. The primary endpoint was progression free survival (PFS). Secondary endpoints were overall response rate, overall survival (OS), duration of response, safety, and tolerability. Ninety-three patients (median age 66.3 years (41.9 – 84.5)) were enrolled with a median follow-up of 26.4 (1.6 – 54.6) months. The median PFS was 22.3 months (95% CI 15.7 – 25.6) with a 46.3% (95% CI 35.1 – 52.8) 2-year PFS. Median OS was not reached and was 73.8% (95% CI 62.9 – 81.9) at 2 years. The overall response rate was 88% (≥ VGPR 73%). There was no difference in the depth of response, PFS or OS comparing Asian and Non-Asian cohorts (p=0.61). The safety profile for KTd was consistent with each individual drug. KTd is well tolerated and effective in patients with RRMM irrespective of Asian or non-Asian ethnicity and provides an alternative option particularly where use of KRd is limited by access, cost, or renal impairment
Reduced Neutrophil Count in People of African Descent Is Due To a Regulatory Variant in the Duffy Antigen Receptor for Chemokines Gene
Persistently low white blood cell count (WBC) and neutrophil count is a well-described phenomenon in persons of African ancestry, whose etiology remains unknown. We recently used admixture mapping to identify an approximately 1-megabase region on chromosome 1, where ancestry status (African or European) almost entirely accounted for the difference in WBC between African Americans and European Americans. To identify the specific genetic change responsible for this association, we analyzed genotype and phenotype data from 6,005 African Americans from the Jackson Heart Study (JHS), the Health, Aging and Body Composition (Health ABC) Study, and the Atherosclerosis Risk in Communities (ARIC) Study. We demonstrate that the causal variant must be at least 91% different in frequency between West Africans and European Americans. An excellent candidate is the Duffy Null polymorphism (SNP rs2814778 at chromosome 1q23.2), which is the only polymorphism in the region known to be so differentiated in frequency and is already known to protect against Plasmodium vivax malaria. We confirm that rs2814778 is predictive of WBC and neutrophil count in African Americans above beyond the previously described admixture association (P = 3.8×10−5), establishing a novel phenotype for this genetic variant
Genome-wide association study identifies 32 novel breast cancer susceptibility loci from overall and subtype-specific analyses.
Breast cancer susceptibility variants frequently show heterogeneity in associations by tumor subtype1-3. To identify novel loci, we performed a genome-wide association study including 133,384 breast cancer cases and 113,789 controls, plus 18,908 BRCA1 mutation carriers (9,414 with breast cancer) of European ancestry, using both standard and novel methodologies that account for underlying tumor heterogeneity by estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 status and tumor grade. We identified 32 novel susceptibility loci (P < 5.0 × 10-8), 15 of which showed evidence for associations with at least one tumor feature (false discovery rate < 0.05). Five loci showed associations (P < 0.05) in opposite directions between luminal and non-luminal subtypes. In silico analyses showed that these five loci contained cell-specific enhancers that differed between normal luminal and basal mammary cells. The genetic correlations between five intrinsic-like subtypes ranged from 0.35 to 0.80. The proportion of genome-wide chip heritability explained by all known susceptibility loci was 54.2% for luminal A-like disease and 37.6% for triple-negative disease. The odds ratios of polygenic risk scores, which included 330 variants, for the highest 1% of quantiles compared with middle quantiles were 5.63 and 3.02 for luminal A-like and triple-negative disease, respectively. These findings provide an improved understanding of genetic predisposition to breast cancer subtypes and will inform the development of subtype-specific polygenic risk scores
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