Band structure of topological insulators from noise measurements in tunnel junctions

The unique properties of spin-polarized surface or edge states in topological insulators (TIs) make these quantum coherent systems interesting from the point of view of both fundamental physics and their implementation in low power spintronic devices. Here we present such a study in TIs, through tunneling and noise spectroscopy utilizing TI/Al$_2$O$_3$/Co tunnel junctions with bottom TI electrodes of either Bi$_2$Te$_3$ or Bi$_2$Se$_3$. We demonstrate that features related to the band structure of the TI materials show up in the tunneling conductance and even more clearly through low frequency noise measurements. The bias dependence of 1/f noise reveals peaks at specific energies corresponding to band structure features of the TI. TI tunnel junctions could thus simplify the study of the properties of such quantum coherent systems, that can further lead to the manipulation of their spin-polarized properties for technological purposes

Effects of basal area on survival and growth of longleaf pine when practicing selection silviculture

Aim of study: Uneven-aged (UEA) management systems can achieve multiple-use objectives, however, use of UEA techniques to manage longleaf pine (Pinus palustris Mill.) forests are still open to question, because of the species’ intolerance of competition. It was our aim to examine the influence of different levels (9.2, 13.8 and 18.4 m2 ha-1) of residual basal area (RBA) on longleaf pine seedling survival and growth following three growing seasons.Area of study: This study was conducted at the Escambia Experimental Forest, located on the Southern Coastal Plain of Alabama, in the southeastern United States.Material and Methods: Selection silviculture was implemented with the Proportional-Basal Area (Pro-B) method. Prescribed burning was conducted before seed dispersal and in the second year after germination. Photosynthetically active radiation (PAR) was measured under the canopy in the study plots. Survival and growth of longleaf pine seedlings were observed for three growing seasons.Main results: An inverse relationship was found between the number of germinants and RBA, but the mortality of germinants and planted seedlings was not affected by RBA. At age three, an inverse relationship was observed between root-collar diameter (RCD) growth of the germinants and RBA, but RCD growth of planted seedlings was not affected by RBA. Most of the study plots contained more than the projected number of seedlings needed to sustain the target diameter structure.Research highlights: Long-term continuous monitoring of seedling development and recruitment into canopy is required to determine the efficacy of UEA management. However, current data suggest that UEA methods may be a viable alternative to the use of even-aged (EA) methods in longleaf ecosystems

Inverse problem and Bertrand's theorem

The Bertrand's theorem can be formulated as the solution of an inverse problem for a classical unidimensional motion. We show that the solutions of these problems, if restricted to a given class, can be obtained by solving a numerical equation. This permit a particulary compact and elegant proof of Bertrand's theorem.Comment: 11 pages, 3 figure

Monitoring of tectonic deformation in the Gulf of California (Mexico) using GPS measurements

International audienceThe Gulf of California, Mexico, was formed by the separation of the peninsular Baja California from North America between 12 and 6 Ma. Its transtensional fault system is composed of an en échelon array of long right-lateral transform fault segments that alternate with short extensionalbasins and spreading ridges. This tectonic setting provides a unique opportunity to study deformation associated with the transition of a continentalstrike-slip fault (the San Andreas Fault) to seafloor spreading (East Pacific Rise) along a rapidly moving fault system. The studied area is composedof the peninsular Baja California and the continental area of the Sonora and Sinaloa states of Mexico. We present the deformation field in the Gulf of California using GPS data observed between 2010 and 2015 and processed using the GAMIT/GLOBK software. The GPS stations used belong to the different networks namely SOPAC, CORS and the Mexican National red (Red Geodésica Activa de Instituto Nacional de Estadística y Geografía). A preliminary analysis of the deformation field will be related to the seismic events in the studied area

Sintesis Paduan Co-cr Menggunakan Metode Ultrasonik

Paduan Co-Cr merupakan material tahan suhu tinggi dan tahan korosi. Penelitian ini bertujuan mensistesis serbuk paduan Co-Cr dengan metode ultrasonik, kemudian dilanjutkan dengan proses sintering dalam kapsul kaca kuarsa. Iradiasi ultrasonik yang digunakan pada frekuensi 20 kHz dan amplitudo 40 % dengan komposisi Co : Cr sebesar 80 : 20.Waktu perlakuan sonikasi adalah selama 0 jam, 3 jam, 6 jam, 12 jam, 24 jam, dan 48 jamdalam larutan etanol. Setelah sonikasi selama 48 jam, fasa FCC dari Co mulai bertransformasi menjadi fasa HCP. Perlakuan ultrasonik terhadap campuran Co-Cr juga memberikan efek pengurangan ukuran partikel. Parameter kisi serbuk setelah ultrasonikasi 48 jam adalah: untuk HCP-Co a = b = 0,25074 nmdan c = 0,40699 nm, untuk FCC-Co a = b = c = 0,35411nm, dan untuk BCC-Cr a=b=c=0.28827 nm. Perlakuan ultrasonik selama 48 jam menhasilkan pembentukan paduan Co-Cr dengan persentasi berat sebesar 25,2124. Hasil sintering padatan Co-Cr menunjukkan parameter kisi HCP-Co memiliki nilai yaitu a = b = 0,25230 nm dan c=0,41223 nm, dan FCC-Co a = b = c = 0,35232 nm. Terbentuknya microalloying CoCr diindikasikan dari hasil EDS, teramati partikel yang mempunyai komposisi Co : Cr = 71,25 : 24,45. Paduan Co-Cr yang terbentuk setelah sintering pada 1300 oC adalah sebesar 15,33416 %berat

SAR-based Wind Resource Statistics in the Baltic Sea

Ocean winds in the Baltic Sea are expected to power many wind farms in the coming years. This study examines satellite Synthetic Aperture Radar (SAR) images from Envisat ASAR for mapping wind resources with high spatial resolution. Around 900 collocated pairs of wind speed from SAR wind maps and from 10 meteorological masts, established specifically for wind energy in the study area, are compared. The statistical results comparing in situ wind speed and SAR-based wind speed show a root mean square error of 1.17 m s−1, bias of −0.25 m s−1, standard deviation of 1.88 m s−1 and correlation coefficient of R2 0.783. Wind directions from a global atmospheric model, interpolated in time and space, are used as input to the geophysical model function CMOD-5 for SAR wind retrieval. Wind directions compared to mast observations show a root mean square error of 6.29° with a bias of 7.75°, standard deviation of 20.11° and R2 of 0.950. The scale and shape parameters, A and k, respectively, from the Weibull probability density function are compared at only one available mast and the results deviate ~2% for A but ~16% for k. Maps of A and k, and wind power density based on more than 1000 satellite images show wind power density values to range from 300 to 800 W m−2 for the 14 existing and 42 planned wind farms

A critical analysis of COVID-19 research literature: Text mining approach

Objective: Among the stakeholders of COVID-19 research, clinicians particularly experience difficulty keeping up with the deluge of SARS-CoV-2 literature while performing their much needed clinical duties. By revealing major topics, this study proposes a text-mining approach as an alternative to navigating large volumes of COVID-19 literature. Materials and methods: We obtained 85,268 references from the NIH COVID-19 Portfolio as of November 21. After the exclusion based on inadequate abstracts, 65,262 articles remained in the final corpus. We utilized natural language processing to curate and generate the term list. We applied topic modeling analyses and multiple correspondence analyses to reveal the major topics and the associations among topics, journal countries, and publication sources. Results: In our text mining analyses of NIH’s COVID-19 Portfolio, we discovered two sets of eleven major research topics by analyzing abstracts and titles of the articles separately. The eleven major areas of COVID-19 research based on abstracts included the following topics: 1) Public Health, 2) Patient Care & Outcomes, 3) Epidemiologic Modeling, 4) Diagnosis and Complications, 5) Mechanism of Disease, 6) Health System Response, 7) Pandemic Control, 8) Protection/Prevention, 9) Mental/Behavioral Health, 10) Detection/Testing, 11) Treatment Options. Further analyses revealed that five (2,3,4,5, and 9) of the eleven abstract-based topics showed a significant correlation (ranked from moderate to weak) with title-based topics. Conclusion: By offering up the more dynamic, scalable, and responsive categorization of published literature, our study provides valuable insights to the stakeholders of COVID-19 research, particularly clinicians.3417985

Natural coagulates for wastewater treatment; a review for application and mechanism

The increase of water demand and wastewater generation is among the global concerns in the world. The less effective management of water sources leads to serious consequences, the direct disposal of untreated wastewater is associated with the environmental pollution, elimination of aquatic life and the spread of deadly epidemics. The flocculation process is one of the most important stages in water and wastewater treatment plants, wherein this phase the plankton, colloidal particles, and pollutants are precipitated and removed. Two major types of coagulants are used in the flocculation process included the chemical and natural coagulants. Many studies have been performed to optimize the flocculation process while most of these studies have confirmed the hazardous effects of chemical coagulants utilization on the ecosystem. This chapter reviews a summary of the coagulation/flocculation processes using natural coagulants as well as reviews one of the most effective natural methods of water and wastewater treatment

Multiband tight-binding theory of disordered ABC semiconductor quantum dots: Application to the optical properties of alloyed CdZnSe nanocrystals

Zero-dimensional nanocrystals, as obtained by chemical synthesis, offer a broad range of applications, as their spectrum and thus their excitation gap can be tailored by variation of their size. Additionally, nanocrystals of the type ABC can be realized by alloying of two pure compound semiconductor materials AC and BC, which allows for a continuous tuning of their absorption and emission spectrum with the concentration x. We use the single-particle energies and wave functions calculated from a multiband sp^3 empirical tight-binding model in combination with the configuration interaction scheme to calculate the optical properties of CdZnSe nanocrystals with a spherical shape. In contrast to common mean-field approaches like the virtual crystal approximation (VCA), we treat the disorder on a microscopic level by taking into account a finite number of realizations for each size and concentration. We then compare the results for the optical properties with recent experimental data and calculate the optical bowing coefficient for further sizes