Sound modes in composite incommensurate crystals

We propose a simple phenomenological model describing composite crystals, constructed from two parallel sets of periodic inter-penetrating chains. In the harmonic approximation and neglecting thermal fluctuations we find the eigenmodes of the system. It is shown that at high frequencies there are two longitudinal sound modes with standard attenuation, while in the low frequency region there is one propagating sound mode and an over-damped phase mode. The crossover between these two regions is analyzed numerically and the dynamical structure factor is calculated. It is shown that the qualitative features of the experimentally observed spectra can be consistently described by our model.Comment: 12 pages, 2 eps figures, Revtex, accepted to European Physics Journal B, (2002

Direct search for Higgs boson in LHCb

The LHCb detector is a forward one-arm spectrometer to precision measurements of CP violation in the B-meson systems. The motivation of the present work is to assess the potential of LHCb to observe a Standard Model (SM) Higgs signal. The recent results obtained at LEP give a hint of a SM Higgs boson with a mass mH = 115.0 +1.3 &#8211;0.9 GeV/c2 with a statistical significance of 2.9 standard deviations. Because of the high longitudinal boost encountered by the products in the pp collisions at LHC, a significant fraction (~30%) of light Higgs (mH = 115 GeV/c2) are produced in the LHCb acceptance 1.8 < h < 4.9. These facts potentially place LHCb in the race for the observation of the SM Higgs. Given a relatively low running luminosity of 2 x 1032 cm-2s-1- compared to the nominal 1034 cm-2s-1 at LHC and a limited geometrical acceptance, we have shown that the channels accessible to LHCb are H + W± Z0 b`b + l± X for Higgs masses in the range 100-130 GeV/c2. This work pioneered a setup for the production and the analysis of hard jets in the LHCb detector. We demonstrated in the full detector simulation that the LHCb baseline design allows to efficiently identify, reconstruct and trigger the b-jets coming from the Higgs. Due to the impossibility to perform a detailed simulation of the huge amount of background, we have developed a "fast simulation" which includes the relevant detector effects. The Higgs analysis requires a hard lepton isolated from the b-jets to reject the QCD background. At this stage, the cut-based study indicates that the dominant background comes from top pairs production. The signal significance is S/sqrt(B) ~0.7 for one LHCb year (integrated luminosity of 2 fb-l). A realistic scheme for b-jets tagging and for the identification of the associated lepton is left for further studies. This work initiated an involved analysis that deserves to be continued. The signal significance is modest, however, potentially large improvements must not be neglected when performing a combined optimization on the discriminating variables. This thesis also suggests some new strategies to enhance the signal significance. Part of the work done for this thesis was the participation in technical developments for LHCb. Appendix C summarizes the activity led in the context of the RD46 collaboration at CERN during the years 1996-1998 to develop the capillary layers technique for tracking purpose in high luminosity environment. The various publications to which the present work contributed are listed at the end of the appendix

The Lausanne Institutional Biobank: a new resource to catalyse research in personalised medicine and pharmaceutical sciences.

Breakthrough technologies which now enable the sequencing of individual genomes will irreversibly modify the way diseases are diagnosed, predicted, prevented and treated. For these technologies to reach their full potential requires, upstream, access to high-quality biomedical data and samples from large number of properly informed and consenting individuals and, downstream, the possibility to transform the emerging knowledge into a clinical utility. The Lausanne Institutional Biobank was designed as an integrated, highly versatile infrastructure to harness the power of these emerging technologies and catalyse the discovery and development of innovative therapeutics and biomarkers, and advance the field of personalised medicine. Described here are its rationale, design and governance, as well as parallel initiatives which have been launched locally to address the societal, ethical and technological issues associated with this new bio-resource. Since January 2013, inpatients admitted at Lausanne CHUV University Hospital have been systematically invited to provide a general consent for the use of their biomedical data and samples for research, to complete a standardised questionnaire, to donate a 10-ml sample of blood for future DNA extraction and to be re-contacted for future clinical trials. Over the first 18 months of operation, 14,459 patients were contacted, and 11,051 accepted to participate in the study. This initial 18-month experience illustrates that a systematic hospital-based biobank is feasible; it shows a strong engagement in research from the patient population in this University Hospital setting, and the need for a broad, integrated approach for the future of medicine to reach its full potential

Optical absorption spectrum of dilute U4+ impurities in incommensurate ThBr4 : lineshape analysis

Crystal-field transitions associated with U4+ impurities diluted in ThBr4 give rise to broad absorption bands characterized by edge singularities. We show that the experimental spectra are consistent with the known occurrence of a sinusoidal distortion which modulates the Br- ion equilibrium positions, thus reducing the actinide site-symmetry from D2d to D2. The observation of spectral singularities corresponding to D2d-sites is interpreted as resulting from the partial pinning of the incommensurate modulation by the U4+ impurities

Thermal conductivity of the thermoelectric layered cobalt oxides measured by the Harman method

In-plane thermal conductivity of the thermoelectric layered cobalt oxides has been measured using the Harman method, in which thermal conductivity is obtained from temperature gradient induced by applied current. We have found that the charge reservoir block (the block other than the CoO$_2$ block) dominates the thermal conduction, where a nano-block integration concept is effective for material design. We have further found that the thermal conductivity shows a small but finite in-plane anisotropy between $a$ and $b$ axes, which can be ascribed to the misfit structure.Comment: 4 pages, 4 figures, J. Appl. Phys. (scheduled on July 1, 2004

The SrTiO3_3 displacive transition revisited by Coherent X-ray Diffraction

We present a Coherent X-ray Diffraction study of the antiferrodistortive displacive transition of SrTiO$_3$, a prototypical example of a phase transition for which the critical fluctuations exhibit two length scales and two time scales. From the microbeam x-ray coherent diffraction patterns, we show that the broad (short-length scale) and the narrow (long-length scale) components can be spatially disentangled, due to 100 $\mu$m-scale spatial variations of the latter. Moreover, both components exhibit a speckle pattern, which is static on a $\sim$10 mn time-scale. This gives evidence that the narrow component corresponds to static ordered domains. We interpret the speckles in the broad component as due to a very slow dynamical process, corresponding to the well-known \emph{central} peak seen in inelastic neutron scattering.Comment: 4 pages, 3 figures, accepted in PR

Modern Humans Did Not Admix with Neanderthals during Their Range Expansion into Europe

The process by which the Neanderthals were replaced by modern humans between 42,000 and 30,000 before present is still intriguing. Although no Neanderthal mitochondrial DNA (mtDNA) lineage is found to date among several thousands of Europeans and in seven early modern Europeans, interbreeding rates as high as 25% could not be excluded between the two subspecies. In this study, we introduce a realistic model of the range expansion of early modern humans into Europe, and of their competition and potential admixture with local Neanderthals. Under this scenario, which explicitly models the dynamics of Neanderthals' replacement, we estimate that maximum interbreeding rates between the two populations should have been smaller than 0.1%. We indeed show that the absence of Neanderthal mtDNA sequences in Europe is compatible with at most 120 admixture events between the two populations despite a likely cohabitation time of more than 12,000 y. This extremely low number strongly suggests an almost complete sterility between Neanderthal females and modern human males, implying that the two populations were probably distinct biological species

SPLATCHE2: a spatially explicit simulation framework for complex demography, genetic admixture and recombination

Summary: SPLATCHE2 is a program to simulate the demography of populations and the resulting molecular diversity for a wide range of evolutionary scenarios. The spatially explicit simulation framework can account for environmental heterogeneity and fluctuations, and it can manage multiple population sources. A coalescent-based approach is used to generate genetic markers mostly used in population genetics studies (DNA sequences, SNPs, STRs or RFLPs). Various combinations of independent, fully or partially linked genetic markers can be produced under a recombination model based on the ancestral recombination graph. Competition between two populations (or species) can also be simulated with user-defined levels of admixture between the two populations. SPLATCHE2 may be used to generate the expected genetic diversity under complex demographic scenarios and can thus serve to test null hypotheses. For model parameter estimation, SPLATCHE2 can easily be integrated into an Approximate Bayesian Computation (ABC) framework. Availability and implementation: SPLATCHE2 is a C++ program compiled for Windows and Linux platforms. It is freely available at www.splatche.com, together with its related documentation and example data. Contact: [email protected]