Towards predictive many-body calculations of phonon-limited carrier mobilities in semiconductors

We probe the accuracy limit of {\it ab initio} calculations of carrier mobilities in semiconductors, within the framework of the Boltzmann transport equation. By focusing on the paradigmatic case of silicon, we show that fully predictive calculations of electron and hole mobilities require many-body quasiparticle corrections to band structures and electron-phonon matrix elements, the inclusion of spin-orbit coupling, and an extremely fine sampling of inelastic scattering processes in momentum space. By considering all these factors we obtain excellent agreement with experiment, and we identify the band effective masses as the most critical parameters to achieve predictive accuracy. Our findings set a blueprint for future calculations of carrier mobilities, and pave the way to engineering transport properties in semiconductors by design.Comment: 11 pages and 8 figure

Blue Shifter: A Reverse Quit Model for Law Enforcement Leaders

Many organizations are currently experiencing the impact of employees quitting their jobs, this reality has left organizations, including police departments, wondering how to slow down the effects of turnover. Employee turnover is witnessed when employees decide to leave their position at the organization and end their work relationship. Turnover can have a detrimental impact on an organization’s finances, employee performance, worker productivity, and customer service. Additionally, turnover is critical to communities since decreased police forces are related to increases in crime. Furthermore, police resignations are higher than ever and are predicted to continue increasing, however, it is not pernicious to all. Some organizations have discovered ways to reverse the intention to quit. This book draws on academic research and three decades of experience in public safety, to introduce some of the best practices to improve police turnover. To impact a police organizational shift and avert good police officers from the intention to quit in a time of intense probes in policing, police organizations will need to change at all levels of the police department, from the police executive to the beat officer on the street. This organizational shift demands a police leader that can motivate and address the needs of the new police officer. This type of leader is called a SHIFTER. The SHIFTER is proposed in a Reverse Quit Model (RQM) consisting of seven practical strategies used to lead: (1) serving (2) humble (3) innovative (4) fun-centered (5) trust-builder (6) empowering and (7) resilience. Serving leaders give what it takes to support their employees, Humble leaders are willing to give up their position or title for the bigger objective, Innovative leaders never stop thinking about ways to develop their organizations, Fun-centered leaders want to maintain joy in the workplace no matter what challenges may bring, Trust-building leaders value relationships and strive to improve them, Empowering leaders will encourage their employees to think, create, and make decisions without or with very little supervision, and Resilient leaders always believe in the intention to succeed or overcome. Resilience is the principal strategy of the model and will be the key ingredient to the SHIFTER. A police organization that focuses on hiring and developing frontline leaders to apply the seven strategies in the RQM is on the right path toward reducing the intention to quit

Ab initio theory of polarons: formalism and applications

We develop a theoretical and computational framework to study polarons in semiconductors and insulators from first principles. Our approach provides the formation energy, excitation energy, and wavefunction of both electron and hole polarons, and takes into account the coupling of the electron or hole to all phonons. An important feature of the present method is that it does not require supercell calculations, and relies exclusively on electron band structures, phonon dispersions, and electron-phonon matrix elements obtained from calculations in the crystal unit cell. Starting from the Kohn-Sham (KS) equations of density-functional theory, we formulate the polaron problem as a variational minimization, and we obtain a nonlinear eigenvalue problem in the basis of KS states and phonon eigenmodes. In our formalism the electronic component of the polaron is expressed as a coherent superposition of KS states, in close analogy with the solution of the Bethe-Salpeter equation for the calculation of excitons. We demonstrate the power of the methodology by studying polarons in LiF and Li2O2. We show that our method describes both small and large polarons, and seamlessly captures Frohlich-type polar electron-phonon coupling and non-Frohlich coupling to acoustic and optical phonons. To analyze in quantitative terms the electron-phonon coupling mechanisms leading to the formation of polarons, we introduce spectral decompositions similar to the Eliashberg spectral function. We validate our theory using both analytical results and direct calculations on large supercells. This study constitutes a first step toward complete ab initio many-body calculations of polarons in real materials.Comment: 26 pages, 8 figure

Ab Initio Phase Diagram of Chromium to 2.5 TPa

Chromium possesses remarkable physical properties such as hardness and corrosion resistance. Chromium is also a very important geophysical material as it is assumed that lighter Cr isotopes were dissolved in the Earth's molten core during the planet's formation, which makes Cr one of the main constituents of the Earth's core. Unfortunately, Cr has remained one of the least studied 3d transition metals. In a very recent combined experimental and theoretical study (Anzellini et al., Scientific Reports, 2022), the equation of state and melting curve of chromium were studied to 150 GPa, and it was determined that the ambient body-centered cubic (bcc) phase of crystalline Cr remains stable in the whole pressure range considered. However, the importance of the knowledge of the physical properties of Cr, specifically its phase diagram, necessitates further study of Cr to higher pressure. In this work, using a suite of ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid-solid phase transition boundaries, we obtain the theoretical phase diagram of Cr to 2.5 TPa. We calculate the melting curves of the two solid phases that are present on its phase diagram, namely, the lower-pressure bcc and the higher-pressure hexagonal close-packed (hcp) ones, and obtain the equation for the bcc-hcp solid-solid phase transition boundary. We also obtain the thermal equations of state of both bcc-Cr and hcp-Cr, which are in excellent agreement with both experimental data and QMD simulations. We argue that 2180 K as the value of the ambient melting point of Cr which is offered by several public web resources ("Wikipedia," "WebElements," "It's Elemental," etc.) is most likely incorrect and should be replaced with 2135 K, found in most experimental studies as well as in the present theoretical work

Next-generation forward genetic screens: using simulated data to improve the design of mapping-by-sequencing experiments in Arabidopsis

Forward genetic screens have successfully identified many genes and continue to be powerful tools for dissecting biological processes in Arabidopsis and other model species. Next-generation sequencing technologies have revolutionized the time-consuming process of identifying the mutations that cause a phenotype of interest. However, due to the cost of such mapping-by-sequencing experiments, special attention should be paid to experimental design and technical decisions so that the read data allows to map the desired mutation. Here, we simulated different mapping-by-sequencing scenarios. We first evaluated which short-read technology was best suited for analyzing gene-rich genomic regions in Arabidopsis and determined the minimum sequencing depth required to confidently call single nucleotide variants. We also designed ways to discriminate mutagenesis-induced mutations from background Single Nucleotide Polymorphisms in mutants isolated in Arabidopsis non-reference lines. In addition, we simulated bulked segregant mapping populations for identifying point mutations and monitored how the size of the mapping population and the sequencing depth affect mapping precision. Finally, we provide the computational basis of a protocol that we already used to map T-DNA insertions with paired-end Illumina-like reads, using very low sequencing depths and pooling several mutants together; this approach can also be used with single-end reads as well as to map any other insertional mutagen. All these simulations proved useful for designing experiments that allowed us to map several mutations in Arabidopsis

Emerging pathogens in the central nervous system: a cerebral abscess by Streptococcus porcinus

Brain abscesses can cause an incapacitating neurological deicit in up to 50% of patients, thus the reduction of these sequelae becomes the main goal of its timely and speciic surgical and medical treatment. With technological advances in bacteriological identiication and diagnostic imaging, the clinical suspicion can be conirmed, and the speciic etiological agent can be identiied in a larger number of cases. New pathogens have emerged through this process, such as Streptococcus porcinus, in which the ability to affect the central nervous system has not been documented. A clinical case is presented of a brain abscess in an immunocompetent patient, and its favorable response to surgical drainage t hrough a skull burr h ole and nee dle aspiration with antibiotic therapy (ceftriaxone, metronidazole and vancomycin) is discussed

A Branch-Price-and-Cut Procedure for the Discrete Ordered Median Problem

International audienceThe Discrete Ordered Median Problem (DOMP) is formulated as a set partitioning problem using an exponential number of variables. Each variable corresponds to a set of demand points allocated to the same facility with the information of the sorting position of their corresponding costs. We develop a column generation approach to solve the continuous relaxation of this model. Then, we apply a branch-price-and-cut algorithm to solve small to large sized instances of DOMP in competitive computational time

Heridas craneales por proyectil de arma de fuego en población civil: análisis de la experiencia de un centro en Monterrey, México

ResumenAntecedentesLas heridas por proyectil de arma de fuego en población civil mexicana eran excepcionales. Actualmente los conflictos entre grupos de delincuencia organizada son con armas consideradas en México como de uso exclusivo del ejército.ObjetivosDescribir nuestra experiencia y compartir el resultado de factores clínicos y radiológicos de influencia en el pronóstico de los pacientes.Material y métodosEstudio observacional, retrospectivo de pacientes con herida craneal por proyectil de arma de fuego penetrando duramadre, tratados de enero de 2009 a enero de 2013, considerando variables: demográficas, escala de coma de Glasgow al ingreso, estado pupilar, tipo de operación y tamaño de descompresión, escala de resultados de Glasgow al egreso y a los 6 meses.ResultadosDe 68 pacientes excluimos a aquellos en los que no hubo penetración de duramadre, quedando 52. Edad promedio de 28.7 años, hombres un 80.8%, todos intervenidos quirúrgicamente y con mortalidad general del 8%. La mortalidad del grupo con escala de coma de Glasgow de 3-5 fue del 43%, de 6-8 fue del 6%, y nula con 9-15. En los pacientes con ambas pupilas fijas, anisocóricas e isocóricas, la mortalidad fue del 67, 7 y 3%, respectivamente. Una trayectoria del proyectil bihemisférica, multilobar y unihemisférica más compromiso ventricular se relacionó con escala de resultados de Glasgow en el momento del egreso≤3 en el 90.9% de los casos.ConclusionesEscala de coma de Glasgow al ingreso y estado pupilar son los factores con mayor influencia en el pronóstico. Pacientes con escala de coma de Glasgow>8 y<13 puntos al ingreso, respuesta pupilar normal y sin compromiso ventricular se pueden beneficiar con tratamiento quirúrgico agresivo temprano.AbstractBackgroundGunshot wounds in civilian population of México were quite rare. Currently, conflicts amongst organized crime groups are carried out with weapons, which are considered as exclusive use by the natiońs army.ObjectivesDescribe the experience of our institution and share results of clinical and radiological factors influencing the prognosis of the patients.Material and methodsObservational and retrospective study of patients with cranial gunshot wounds (GSW), which penetrated the duramater, treated from January 2009 - January 2013. We considered several demographic variables, Glasgow Coma Scale (GCS), upon admission, state of pupils, type of surgery and size of decompression, Glasgow Outcome Score (GOS) upon discharge, and after 6 months.ResultsOf 68 patients, we excluded those whose duramater was not penetrated, leaving 52 patients. The average age was 28.7 years, and 80.8% were males. All were surgically intervened, with 8% of general mortality. Mortality in the GCS 3 to 5 points group was 43%, from the 6 to 8 points it was 6%, and no deaths in the 9 to 15 points. In patients with both pupils fixed, anisocoric and isocoric, mortality was 67%, 7%, and 3%, respectively. Bihemispheric, multilobar and unihemispheric trajectory of the bullet plus ventricular compromise was related to a Glasgow Outcome Score ≤ 3 upon discharge in 90.9% of the cases.ConclusionsGCS upon admission and state of the pupils are the most influential factors in the prognosis. Patients with a GCS > 8 < 13 points upon admission, normal pupillary response, without ventricular compromise can benefit with early and aggressive surgical treatment