Cosmological and Black Hole Spacetimes in Twisted Noncommutative Gravity

We derive noncommutative Einstein equations for abelian twists and their solutions in consistently symmetry reduced sectors, corresponding to twisted FRW cosmology and Schwarzschild black holes. While some of these solutions must be rejected as models for physical spacetimes because they contradict observations, we find also solutions that can be made compatible with low energy phenomenology, while exhibiting strong noncommutativity at very short distances and early times.Comment: LaTeX 12 pages, JHEP.st

Noncommutative Solitons of Gravity

We investigate a three-dimensional gravitational theory on a noncommutative space which has a cosmological constant term only. We found various kinds of nontrivial solutions, by applying a similar technique which was used to seek noncommutative solitons in noncommutative scalar field theories. Some of those solutions correspond to bubbles of spacetimes, or represent dimensional reduction. The solution which interpolates $G_{\mu\nu}=0$ and Minkowski metric is also found. All solutions we obtained are non-perturbative in the noncommutative parameter $\theta$, therefore they are different from solutions found in other contexts of noncommutative theory of gravity and would have a close relation to quantum gravity.Comment: 29 pages, 5 figures. v2: minor corrections done in Section 3.1 and Appendix, references added. v3, v4: typos correcte

Coulomb Explosion and Thermal Spikes

A fast ion penetrating a solid creates a track of excitations. This can produce displacements seen as an etched track, a process initially used to detect energetic particles but now used to alter materials. From the seminal papers by Fleischer et al. [Phys. Rev. 156, 353 (1967)] to the present [C. Trautmann, S. Klaumunzer and H. Trinkaus, Phys. Rev. Lett. 85, 3648 (2000)], `Coulomb explosion' and thermal spike models are treated as conflicting models for describing ion track effects. Here molecular dynamics simulations of electronic-sputtering, a surface manifestation of ion track formation, show that `Coulomb explosion' produces a `heat' spike so that these are early and late aspects of the same process. Therefore, differences in scaling are due to the use of incomplete spike models.Comment: Submitted to PRL. 4 pages, 3 figures. For related movies see: http://dirac.ms.virginia.edu/~emb3t/coulomb/coulomb.html PACS added in new versio

Associações genômicas para perímetro escrotal ao desmame em bovinos da raça Canchim.

O objetivo deste trabalho foi estudar a associação entre polimorfismos de base única (SNP) com os valores genéticos do perímetro escrotal mensurado ao desmame (PED) em bovinos de corte de raça sintética. Neste estudo foram utilizados 285 animais da raça Canchim e 114 animais do grupo genético MA (utilizados na formação da raça Canchim), genotipados com o painel de alta densidade (786.799 SNPs). Após o controle de qualidade de informações (genótipos e fenótipos) restaram 672.778 SNPs e 392 animais. Foram observadas associações para PED nos cromossomos 20 e 28. Após a correção para múltiplos testes (?false discovery rate?) ao nível de 10%, 12 SNPs foram significativamente associados, ao longo do cromossomo, com PED. Novos e promissores genes associados com características reprodutivas foram identificados, como os genes SRD5A1 (steroid-5- alpha-reductase, alpha polypeptide 1), NSUN2 (NOP2/Sun domain family, member 2) e LOC100297493 (Odorant-binding protein-like). Estes genes podem ser destacados, pois os dois primeiros parecem atuar no crescimento corporal; desenvolvimento do sistema reprodutivo de machos devido à produção de hormônios andrógenos e espermatogênese; enquanto que o último atua no sistema olfativo. As regiões polimórficas identificadas apresentaram funções moleculares e processos biológicos que podem estar envolvidas na manutenção do organismo e no desempenho reprodutivo de machos. Genes associados à processos hormonais poderiam ser utilizados como genes candidatos para a melhoria do desempenho reprodutivo na raça Canchim. No entanto, é necessária a validação destes resultados em outra população de bovinos Canchim para confirmação das associações genômica

Estudo de associações genômicas para idade ao primeiro e segundo parto em bovinos da raça Canchim.

Recentemente, programas de melhoramento genético de bovinos de corte têm dado maior ênfase para características reprodutivas de fêmeas devido à sua importância econômica para o sistema de produção. O objetivo deste trabalho foi estudar a associação entre polimorfismos de base única (SNP) com os valores genéticos das características idade ao primeiro (IPP) e segundo (ISP) parto em bovinos de corte de raça sintética. Neste estudo foram utilizados 285 animais da raça Canchim e 114 animais do grupo genético MA (utilizados na formação da raça Canchim), genotipados com o painel de alta densidade (786.799 SNPs). Após o controle de qualidade de informações (genótipos e fenótipos) restaram 672.778 SNPs e 392 animais. Foram observadas associações para IPP nos cromossomos 4 e 27, e para ISP nos cromossomos 10, 11 e 15. Após a correção para múltiplos testes (?false discovery rate?) ao nível de 10%, seis e quatro SNPs foram significativamente associados, ao longo do cromossomo, com IPP e ISP. Novos e promissores genes associados com características reprodutivas foram identificados, como os genes SLC8A1 e UBQLN3. Com base nas análises de associação entre SNPs e as características estudadas, verificou-se que os SNPs observados como significativos poderiam ser utilizados na seleção genômica da raça Canchim. As regiões polimórficas identificadas apresentaram funções moleculares e processos biológicos que podem estar envolvidos na manutenção do organismo e no desempenho reprodutivo. Os genes associados à IPP e ISP poderiam ser utilizados como genes candidatos para a melhoria do desempenho de fêmeas e, indiretamente, de machos. A validação destes resultados em outra população de bovinos Canchim deve ser conduzida futuramente para confirmação das associações genômicas

Spatially-resolved decoherence of donor spins in silicon strained by a metallic electrode

Electron spins are amongst the most coherent solid-state systems known, however, to be used in devices for quantum sensing and information processing applications, they must be typically placed near interfaces. Understanding and mitigating the impacts of such interfaces on the coherence and spectral properties of electron spins is critical to realize such applications, but is also challenging: inferring such data from single-spin studies requires many measurements to obtain meaningful results, while ensemble measurements typically give averaged results that hide critical information. Here, we report a comprehensive study of the coherence of near-surface bismuth donor spins in 28-silicon at millikelvin temperatures. In particular, we use strain-induced frequency shifts caused by a metallic electrode to make spatial maps of spin coherence as a function of depth and position relative to the electrode. By measuring magnetic-field-insensitive clock transitions we separate magnetic noise caused by surface spins from charge noise. Our results include quantitative models of the strain-split spin resonance spectra and extraction of paramagnetic impurity concentrations at the silicon surface. The interplay of these decoherence mechanisms for such near-surface electron spins is critical for their application in quantum technologies, while the combination of the strain splitting and clock transition extends the coherence lifetimes by up to two orders of magnitude, reaching up to 300 ms at a mean depth of only 100nm. The technique we introduce here to spatially map coherence in near-surface ensembles is directly applicable to other spin systems of active interest, such as defects in diamond, silicon carbide, and rare earth ions in optical crystals.Comment: 16 pages, 11 figure

Asymptotic expansion for reversible A + B <-> C reaction-diffusion process

We study long-time properties of reversible reaction-diffusion systems of type A + B C by means of perturbation expansion in powers of 1/t (inverse of time). For the case of equal diffusion coefficients we present exact formulas for the asymptotic forms of reactant concentrations and a complete, recursive expression for an arbitrary term of the expansions. Taking an appropriate limit we show that by studying reversible reactions one can obtain "singular" solutions typical of irreversible reactions.Comment: 6 pages, no figures, to appear in PR

Design and Implementation of a Thomson Parabola for Fluence Dependent Energy-Loss Measurements at the Neutralized Drift Compression eXperiment

The interaction of ion beams with matter includes the investigation of the basic principles of ion stopping in heated materials. An unsolved question is the effect of different, especially higher, ion beam fluences on ion stopping in solid targets. This is relevant in applications such as in fusion sciences. To address this question, a Thomson parabola was built for the Neutralized Drift Compression eXperiment (NDCX-II) for ion energy-loss measurements at different ion beam fluences. The linear induction accelerator NDCX-II delivers 2 ns short, intense ion pulses, up to several tens of nC/pulse, or 10$^{10}$-10$^{11}$ ions, with a peak kinetic energy of ~1.1 MeV and a minimal spot size of 2 mm FWHM. For this particular accelerator the energy determination with conventional beam diagnostics, for example, time of flight measurements, is imprecise due to the non-trivial longitudinal phase space of the beam. In contrast, a Thomson parabola is well suited to reliably determine the beam energy distribution. The Thomson parabola differentiates charged particles by energy and charge-to-mass ratio, through deflection of charged particles by electric and magnetic fields. During first proof-of-principle experiments, we achieved to reproduce the average initial helium beam energy as predicted by computer simulations with a deviation of only 1.4 %. Successful energy-loss measurements with 1 {\mu}m thick Silicon Nitride foils show the suitability of the accelerator for such experiments. The initial ion energy was determined during a primary measurement without a target, while a second measurement, incorporating the target, was used to determine the transmitted energy. The energy-loss was then determined as the difference between the two energies