Electronic structure and spectroscopy of the quaternary Heusler alloy Co2_2Cr1−x_{1-x}Fex_{x}Al

Quaternary Heusler alloys Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe ratio $x$ were investigated experimentally and theoretically. The electronic structure and spectroscopic properties were calculated using the full relativistic Korringa-Kohn-Rostocker method with coherent potential approximation to account for the random distribution of Cr and Fe atoms as well as random disorder. Magnetic effects are included by the use of spin dependent potentials in the local spin density approximation. Magnetic circular dichroism in X-ray absorption was measured at the $L_{2,3}$ edges of Co, Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to determine element specific magnetic moments. Calculations and measurements show an increase of the magnetic moments with increasing iron content. Resonant (560eV - 800eV) soft X-ray as well as high resolution - high energy ($\geq 3.5$keV) hard X-ray photo emission was used to probe the density of the occupied states in Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al.Comment: J.Phys.D_Appl.Phys. accepte

Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces

We investigate the transport properties of a ferromagnet-superconductor interface within the framework of a modified three-dimensional Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge inhomogeneity forms via two unique transport mechanisms, namely, evanescent Andreev reflection and evanescent quasiparticle transmission. Furthermore, we take into account the influence of charge inhomogeneity on the interfacial barrier potential and calculate the conductance as a function of bias voltage. Point-contact Andreev reflection (PCAR) spectra often show dip structures, large zero-bias conductance enhancement, and additional zero-bias conductance peak. Our results indicate that transport-induced charge inhomogeneity could be a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure

Design of magnetic materials: Co2_2Cr1−x_{1-x}Fex_{x}Al

Doped Heusler compounds Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe ratio $x$ were investigated experimentally and theoretically. The electronic structure of the ordered, doped Heusler compound Co$_2$Cr$_{1-x}$Fe$_{x}$Al ($x=n/4, n=0,1,2,3,4)$ was calculated using different types of band structure calculations. The ordered compounds turned out to be ferromagnetic with small Al magnetic moment being aligned anti-parallel to the 3d transition metal moments. All compounds show a gap around the Fermi-energy in the minority bands. The pure compounds exhibit an indirect minority gap, whereas the ordered, doped compounds exhibit a direct gap. Magnetic circular dichroism (MCD) in X-ray absorption spectra was measured at the $L_{2,3}$ edges of Co, Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to determine element specific magnetic moments. Calculations and measurements show an increase of the magnetic moments with increasing iron content. The experimentally observed reduction of the magnetic moment of Cr can be explained by Co-Cr site-disorder. The presence of the gap in the minority bands of Co$_2$CrAl can be attributed to the occurrence of pure Co$_2$ and mixed CrAl (001)-planes in the $L2_1$ structure. It is retained in structures with different order of the CrAl planes but vanishes in the $X$-structure with alternating CoCr and CoAl planes.Comment: corrected author lis

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Evaluation of Electrochemotherapy with Bleomycin in the Treatment of Colorectal Hepatic Metastases in a Rat Model

Background: The available ablative procedures for the treatment of hepatic cancer have contraindications due to the heat-sink effect and the risk of thermal injuries. Electrochemotherapy (ECT) as a nonthermal approach may be utilized for the treatment of tumors adjacent to high-risk regions. We evaluated the effectiveness of ECT in a rat model. Methods: WAG/Rij rats were randomized to four groups and underwent ECT, reversible electroporation (rEP), or intravenous injection of bleomycin (BLM) eight days after subcapsular hepatic tumor implantation. The fourth group served as Sham. Tumor volume and oxygenation were measured before and five days after the treatment using ultrasound and photoacoustic imaging; thereafter, liver and tumor tissue were additionally analysed by histology and immunohistochemistry. Results: The ECT group showed a stronger reduction in tumor oxygenation compared to the rEP and BLM groups; moreover, ECTtreated tumors exhibited the lowest levels of hemoglobin concentration compared to the other groups. Histological analyses further revealed a significantly increased tumor necrosis of >85% and a reduced tumor vascularization in the ECT group compared to the rEP, BLM, and Sham groups. Conclusion: ECT is an effective approach for the treatment of hepatic tumors with necrosis rates >85% five days following treatment

Indications on self mode-locking in a broad area single-section quantum dot laser

Broad-area edge-emitting monolithic mode-locked semiconductor quantum dot lasers emitting at 1.26 μm could potentially serve as ideal sources for the generation of high power broad optical frequency combs for short-reach inter and intra data-center links. In this contribution, the inter-mode beat frequency of a 2 mm long InAs/InGaAs quantum dot laser with a broad-ridge waveguide are studied experimentally. Laser output power, radio-frequency and spectral domain analysis is performed. -3 dB spectral widths ranging from 2nm to 5.3 nm and the existence of an inter-mode beat frequency at 20.4 GHz with a signal-to-noise ratio from 2 dB up to 11 dB are experimentally confirmed for injection currents from 0.225 A to 1 A. Our results indicate a potential way towards high output power optical frequency comb generation by electrically injected monolithic semiconductor lasers

Passive mode-locking of p-doped quantum dot semiconductor lasers

Quantum dot based monolithic edge-emitting semiconductor lasers at 1.25 µm are ideal sources for the generation of broad optical frequency combs for optical communication applications. In this work, InAs/InGaAs quantum dot lasers with different total laser length to absorber length ratio and with different p-doping concentrations in the GaAs barrier sections are investigated experimentally in dependence on the gain injection current and absorber reverse bias voltage. A smaller mode-locking area is found for the p-doped device in dependence on the laser biasing conditions. For the undoped active region 1.3 ps short pulse widths at a pulse repetition rate of 20 GHz with a pulse-to-pulse timing jitter of 111 fs are reported for an absorber section length of 12% to the total cavity length. For an undoped and p-doped device short pulse emission between 2.5 ps and 5.5 ps is attained and a shorter absorber section length of 8% or 5%

Identifying Farming Strategies Associated With Achieving Global Agricultural Sustainability

Sustainable agroecosystems provide adequate food while supporting environmental and human wellbeing and are a key part of the United Nations Sustainable Development Goals (SDGs). Some strategies to promote sustainability include reducing inputs, substituting conventional crops with genetically modified (GM) alternatives, and using organic production. Here, we leveraged global databases covering 121 countries to determine which farming strategies—the amount of inputs per area (fertilizers, pesticides, and irrigation), GM crops, and percent agriculture in organic production—are most correlated with 12 sustainability metrics recognized by the United Nations Food and Agriculture Organization. Using quantile regression, we found that countries with higher Human Development Indices (HDI) (including education, income, and lifespan), higher-income equality, lower food insecurity, and higher cereal yields had the most organic production and inputs. However, input-intensive strategies were associated with greater agricultural greenhouse gas emissions. In contrast, countries with more GM crops were last on track to meeting the SDG of reduced inequalities. Using a longitudinal analysis spanning 2004–2018, we found that countries were generally decreasing inputs and increasing their share of agriculture in organic production. Also, in disentangling correlation vs. causation, we hypothesize that a country's development is more likely to drive changes in agricultural strategies than vice versa. Altogether, our correlative analyses suggest that countries with greater progress toward the SDGs of no poverty, zero hunger, good health and wellbeing, quality education, decent work, economic growth, and reduced inequalities had the highest production of organic agriculture and, to a lesser extent, intensive use of inputs

Vertical distribution and migration of fish larvae in the NW Iberian upwelling system during the winter mixing period: implications for cross-shelf distribution

The vertical distribution and vertical migrations of fish larvae and implications for their cross-shelf distribution were investigated in the northern limit of the NE Atlantic upwelling region during the late winter mixing period of 2012. The average positive values of the upwelling index for February and March of this year were far from normal, although the average hydrographic conditions during the period of study were of downwelling and the water column was completely mixed. Fish larvae, most in the preflexion stage, were concentrated in the upper layers of the water column and their distribution was depth stratified, both day and night. However, the larval fish community was not structured in the vertical plane and fish larvae did not show significant diel vertical migration (DVM), although five species showed ontogenetic vertical migration. In regions of coastal upwelling and in the absence of DVM, the location of fish larvae in the water column is crucial for their cross-shelf distribution. Thus, the cross-shelf distribution of the six most abundant species collected in this study can be explained by the surface onshore flow associated with coastal downwelling, retaining larvae of the coastal spawning species with a relatively shallow distribution in the shelf region and transporting larvae of slope spawning species onto the shelf. The wide vertical distribution shown by larvae of the offshore spawning species could be an adaptation of these species to ensure that some larvae reach the inshore nursery areasPlan Nacional de I+D+i (CRAMERCTM2010- 21856-CO3-02), Junta de Galicia (ECOPREGA-10MMA602021PR), Principado de Asturias (GRUPIN14-144)Postprint2,044

Fluctuations in active membranes

Active contributions to fluctuations are a direct consequence of metabolic energy consumption in living cells. Such metabolic processes continuously create active forces, which deform the membrane to control motility, proliferation as well as homeostasis. Membrane fluctuations contain therefore valuable information on the nature of active forces, but classical analysis of membrane fluctuations has been primarily centered on purely thermal driving. This chapter provides an overview of relevant experimental and theoretical approaches to measure, analyze and model active membrane fluctuations. In the focus of the discussion remains the intrinsic problem that the sole fluctuation analysis may not be sufficient to separate active from thermal contributions, since the presence of activity may modify membrane mechanical properties themselves. By combining independent measurements of spontaneous fluctuations and mechanical response, it is possible to directly quantify time and energy-scales of the active contributions, allowing for a refinement of current theoretical descriptions of active membranes.Comment: 38 pages, 9 figures, book chapte