Dependent Transport Research Articles

Transmission-path dependent electron hopping transport in thin films and nanorods of NiO

The present study demonstrates how the length and dimensionality of electron transmission-paths and temperature impact the electron hopping transport in NiO thin films and nanorods. The NiO nanorods and thin films of varying thicknesses were synthesized using physical vapor deposition techniques. The thin films of various thicknesses offer two-dimensional (2D) transmission-paths of varying lengths, whereas nanorods provide confined one-dimensional (1D) transmission-paths for the conduction of electrons. Also, the current-voltage characteristics of 2D and 1D transmission-paths in thin films and nanorods are measured at varying temperatures. The thin films and nanorods of NiO display a characteristic transition in conduction of electrons at a temperature of ∼180 K, which distinguishes the two kinds of electron conduction mechanisms, viz., the nearest-neighbor hopping (NNH) and variable range hopping (VRH). The analysis of the NNH and VRH mechanism quantifies the activation energy, localization lengths, probable hopping distance, and hopping energy of electrons through 2D and 1D transmission-paths at various temperatures. The quantification of these various figure-of-merits proves that the electron hopping transport in nanorods and thin films is quintessentially influenced due to the lengths and dimensionality of transmission-paths and temperature.

Molecular Mechanism of Iron Transport Systems in Vibrio

The ability to acquire iron from the environment is often an important virulence factor for pathogenic bacteria and Vibrios are no exception to this. Vibrios are reported mainly from marine habitats and most of the species are pathogenic. Among those, the pathogenic vibrios eg. V cholerae, V. parahaemolyticus, V. vulnificus causes foodborne illnesses. Vibrios are capable of producing all different classes of siderophores like hydroxamate (aerobactin), catecholate (vibriobactin, fluvibactin), carboxylate (vibrioferrin), and amphiphilic (amphibactin). Every different species of vibrios are capable of utilizing some endogenous or xenosiderophores. Being Gram-negative bacteria, Vibrios import iron siderophore via TonB dependent transport system and unlike other Gamma proteobacteria these usually possess two or even three partially redundant TonB systems for iron siderophore transport. Other than selected few iron siderophores, most pathogenic Vibrios are known to be able to utilize heme as the sole iron source, while some species are capable of importing free iron from the environment. As per the present knowledge, the spectrum of iron compound transport and utilization in Vibrios is better understood than the siderophore biosynthetic capability of individual species.

Extracellular vesicles from hypoxia-preconditioned mesenchymal stem cells alleviates myocardial injury by targeting thioredoxin-interacting protein-mediated hypoxia-inducible factor-1α pathway.

BACKGROUNDExtracellular vesicles (EVs) derived from hypoxia-preconditioned (HP) mesenchymal stem cells (MSCs) have better cardioprotective effects against myocardial infarction (MI) in the early stage than EVs isolated from normoxic (NC)-MSCs. However, the cardioprotective mechanisms of HP-EVs are not fully understood.AIMTo explore the cardioprotective mechanism of EVs derived from HP MSCs.METHODSWe evaluated the cardioprotective effects of HP-EVs or NC-EVs from mouse adipose-derived MSCs (ADSCs) following hypoxia in vitro or MI in vivo, in order to improve the survival of cardiomyocytes (CMs) and restore cardiac function. The degree of CM apoptosis in each group was assessed by the terminal deoxynucleotidyl transferase dUTP nick end-labeling and Annexin V/PI assays. MicroRNA (miRNA) sequencing was used to investigate the functional RNA diversity between HP-EVs and NC-EVs from mouse ADSCs. The molecular mechanism of EVs in mediating thioredoxin-interacting protein (TXNIP) was verified by the dual-luciferase reporter assay. Co-immunoprecipitation, western blotting, and immunofluorescence were performed to determine if TXNIP is involved in hypoxia-inducible factor-1 alpha (HIF-1α) ubiquitination and degradation via the chromosomal region maintenance-1 (CRM-1)-dependent nuclear transport pathway.RESULTSHP-EVs derived from MSCs reduced both infarct size (necrosis area) and apoptotic degree to a greater extent than NC-EVs from CMs subjected to hypoxia in vitro and mice with MI in vivo. Sequencing of EV-associated miRNAs showed the upregulation of 10 miRNAs predicted to bind TXNIP, an oxidative stress-associated protein. We showed miRNA224-5p, the most upregulated miRNA in HP-EVs, directly combined the 3’ untranslated region of TXNIP and demonstrated its critical protective role against hypoxia-mediated CM injury. Our results demonstrated that MI triggered TXNIP-mediated HIF-1α ubiquitination and degradation in the CRM-1-mediated nuclear transport pathway in CMs, which led to aggravated injury and hypoxia tolerance in CMs in the early stage of MI. CONCLUSIONThe anti-apoptotic effects of HP-EVs in alleviating MI and the hypoxic conditions of CMs until reperfusion therapy may partly result from EV miR-224-5p targeting TXNIP.

Temperature dependent carrier transport in few-layered MoS2: from hopping to band transport

Understanding the carrier transport mechanisms is critical for electronic devices based on 2D semiconductors. Here, using a two-terminal device configuration, we show that the carrier transport behaviours in chemical vapour deposited few-layer MoS2 transition from resonant tunnelling to hopping, and eventually to band transport as the temperature increases from 5 K to 370 K. Specifically, the transport in the channel is dominated by resonant tunnelling when T < 30 K is reflected in the temperature-independent conductance. At 50 K < T < 110 K, the channel conductance exhibits a dependence of exp(T 1/2), a signature of Efros–Shklovskii type variable range hopping (VRH). At 110 K < T < 160 K, carrier transport behaves in a transition region with potential attribution to Mott-type VRH. At 160 K < T < 210 K, the nearest neighbour hopping mechanism is confirmed by the linear dependence from the resistance curve derivative analysis. For VRH, the localization length, hopping distance and energy, Coulomb gap energy and density of states are extracted. At T > 210 K, the carrier transport is dominated by thermally activated band transport based on AC conductance and mobility analysis. These findings are significant for revealing the material properties for future 2D semiconductor device applications.

Spatiotemporally controlled room-temperature exciton transport under dynamic strain

Two-dimensional transition metal dichalcogenides (TMDs) provide an attractive platform for studying strain dependent exciton transport at room temperature due to large exciton binding energy and strong bandgap sensitivity to mechanical stimuli. Here, we use Rayleigh type surface acoustic wave (SAW) to demonstrate controlled and directional exciton transport under weak coupling regime at room temperature. We screen the in-plane piezoelectric field using photogenerated carriers to study transport under type-I bandgap modulation and measure a maximum exciton drift velocity of 600 m/s. Furthermore, we demonstrate precise steering of exciton flux by controlling the relative phase between the input RF excitation and exciton photogeneration. The results provide important insight into the weak coupling regime between dynamic strain wave and room temperature excitons in a 2D semiconductor system and pave way to exciting applications of excitonic devices in data communication and processing, sensing and energy conversion.

Demonstration of reconfigurable magnetic tunnel diode and giant tunnel magnetoresistance in magnetic tunnel junctions made with spin gapless semiconductor and half-metallic Heusler alloy

Here, we report fabrication of a high quality exchanged biased trilayer magnetic tunnel junction (MTJ) utilizing a magnetron sputtering system. The MTJ is composed of a type-II spin gapless semiconductor (SGS) Ti2CoSi inverse Heusler alloy (used as a lower electrode), a thin MgO layer (used as a tunnel barrier), and a half-metallic ferromagnet (HMF) Co2MnSi Heusler alloy (used as an upper electrode). Spin dependent transport properties reveal that the micro-fabricated MTJ can act as a reconfigurable magnetic tunnel diode, which lets the electric current to flow in either the forward or reverse path relying on the relative alignment of the magnetization direction of the upper and lower magnetic electrodes. A considerably high on/off current ratio (∼103) and a significantly low turn on voltage (VT) of 0.09 V have been achieved at 5 K for both parallel and antiparallel configurations. Another important characteristic shown by our fabricated MTJ is that it exhibits extremely large tunnel magnetoresistance ratios of 892% at 5 K and 197% at room temperature, which brings to light the utmost importance of using the combination of HMF and SGS materials as magnetic electrodes in a tunnel junction for potential applications in modern spintronic devices. All these exceptional features can undoubtedly nominate CMS/MgO/TCS MTJs as a promising candidate to serve as memory or logic elements in next generation ultra-high density magnetoresistive random access memories together with contemporary spin based electronic devices.

Dominant negative mutation in oxalate transporter SLC26A6 associated with enteric hyperoxaluria and nephrolithiasis

BackgroundNephrolithiasis (NL) is a complex multifactorial disease affecting up to 10%–20% of the human population and causing a significant burden on public health systems worldwide. It results from a combination...

Coordination of two kinesin superfamily motor proteins, KIF3A and KIF13A, is essential for pericellular matrix degradation by membrane-type 1 matrix metalloproteinase (MT1-MMP) in cancer cells

MT1-MMP plays a crucial role in promoting the cellular invasion of cancer cells by degrading the extracellular matrix to create a path for migration. During this process, its localization at the leading edge of migrating cells is critical, and it is achieved by targeted transport of MT1-MMP-containing vesicles along microtubules by kinesin superfamily motor proteins (KIFs). Here we identified three KIFs involved in MT1-MMP vesicle transport: KIF3A, KIF13A, and KIF9. Knockdown of KIF3A and KIF13A effectively inhibited MT1-MMP-dependent collagen degradation and invasion, while knockdown of KIF9 increased collagen degradation and invasion. Our data suggest that KIF3A/KIF13A dependent MT1-MMP vesicles transport takes over upon KIF9 knockdown. Live-cell imaging analyses have indicated that KIF3A and KIF13A coordinate to transport the same MT1-MMP-containing vesicles from the trans-Golgi to the endosomes, and KIF13A alone transports the vesicle from the endosome to the plasma membrane. Taken together, we have identified a unique interplay between three KIFs to regulate leading edge localization of MT1-MMP and MT1-MMP-dependent cancer cell invasion.

Insights into the Na+-dependent transport in SLC4 proteins from a cryo-EM structure of the NDCBE transporter and computational modelling

SLC4 transporters are involved in transport of Cl-, HCO3-, CO32-, Na+, H+, and NH3 through the membrane and are key for pH maintenance and ion homeostasis in the body. Despite their high sequence identity, the members of the family demonstrate an array of transport modes - Na+-dependent or independent transport, H+ and NH3 transport, Na+-anion symport, anion exchange and combinations thereof. Two structures of SLC4 transporters, the human anion exchanger 1 (AE1) and the human sodium carbonate electrogenic symporter 1 (NBCe1), have been previously resolved in their outward facing (OF) open state by X-Ray and cryo-EM, and putative binding sites have been determined from functional mutagenesis and computational modelling.

Huntingtin S421 phosphorylation and expression levels differentially affect signalling and degradative intracellular cargoes

Huntingtin phosphorylation and expression levels modulate endosome motility. Huntingtin acts as a scaffolding protein that recruits motor proteins to vesicular cargoes, enabling it to regulate kinesin- and dynein- dependent transport. The cell precisely regulates motor activity through post-translational modifications of scaffolding molecules including htt. We used CRISPR/Cas9 to induce a phosphomimetic mutation of the endogenous huntingtin at S421 (htt-S421D). This approach allowed us to maintain endogenous expression levels to avoid perturbing the stoichiometry of huntingtin and its many interacting partners.

Structural characterization of the reaction cycle of bacterial DASS dicarboxylate transporters

Na+-dependent dicarboxylate transporter from Vibrio cholerae (VcINDY) imports nutrients across the inner membrane into the cell. The protein is a prototype for the divalent anion sodium symporter (DASS) family, which also includes another group, the Na+-independent dicarboxylate/ dicarboxylate antiporters. Both groups form homodimers, with a scaffold domain and an elevator domain. Using X-ray crystallography and cryo-EM, we have determined multiple state structures of VcINDY and LaINDY, a dicarboxylate antiporter from Lactobacillus acidophilus.

A review on bacterial redox dependent iron transporters and their evolutionary relationship

Iron is an essential yet toxic micronutrient and its transport across biological membranes is tightly regulated in all living organisms. One such iron transporter, the Ftr-type permeases, is found in both eukaryotic and prokaryotic cells. These Ftr-type transporters are required for iron transport, predicted to form α-helical transmembrane structures, and conserve two ArgGluxxGlu (x = any amino acid) motifs. In the yeast Ftr transporter (Ftr1p), a ferroxidase (Fet3p) is required for iron transport in an oxidation coupled transport step. None of the bacterial Ftr-type transporters (EfeU and FetM from E. coli; cFtr from Campylobacter jejuni; FtrC from Brucella, Bordetella, and Burkholderia spp.) contain a ferroxidase protein. Bioinformatics report predicted periplasmic EfeO and FtrB (from the EfeUOB and FtrABCD systems) as novel cupredoxins. The Cu2+ binding and the ferrous oxidation properties of these proteins are uncharacterized and the other two bacterial Ftr-systems are expressed without any ferroxidase/cupredoxin, leading to controversy about the mode of function of these transporters. Here, we review published data on Ftr-type transporters to gain insight into their functional diversity. Based on original bioinformatics data presented here evolutionary relations between these systems are presented.

Spin transport in epitaxial Fe3O4/GaAs lateral structured devices

Research in the spintronics community has been intensively stimulated by the proposal of the spin field-effect transistor (SFET), which has the potential for combining the data storage and process in a single device. Here we report the spin dependent transport on a Fe3O4/GaAs based lateral structured device. Parallel and antiparallel states of two Fe3O4 electrodes are achieved. A clear MR loop shows the perfect butterfly shape at room temperature, of which the intensity decreases with the reducing current, showing the strong bias dependence. Understanding the spin-dependent transport properties in this architecture has strong implication in further development of the spintronic devices for room-temperature SFETs.

Temperature Dependent Carrier Transport in Hydrogenated Amorphous Semiconductors for Thin Film Memristive Applications

This paper demonstrates the transport of electron and hole carriers in two distinct hydrogenated amorphous semiconductor materials at different temperatures. Compared to crystalline materials, the amorphous semiconductors differ structurally, optically and electrically, hence the nature of carrier transport through such amorphous materials differ. Materials like hydrogenated amorphous silicon and amorphous IGZO have been used for the study of temperature dependent carrier transport in this paper. Simulation results have been presented to show the variation of free electron and hole concentration, trapped electron and hole concentration with energy at 300K for both the materials. The change in mobility with a change in the Fermi level has been plotted for different temperatures. The effect of temperature on Brownian motion mobility of electrons and holes in hydrogenated amorphous silicon and amorphous IGZO has been demonstrated towards the end of this paper.

Energy Efficient Hop-by-Hop Retransmission and Congestion Mitigation of an Optimum Routing and Clustering Protocol for WSNs

In the past few decades, wireless sensor networks, which take a growing number of applications in the surroundings further than the human reach, have risen in popularity. Various routing pseudo codes have been suggested for network optimization, emphasizing energy efficiency, network longevity, and clustering processes. To the existing load balancing energy-efficient sleep awake, aware smart sensor network routing protocol, the modified load-balancing efficient-energy sleep active alert smart routing system for wireless sensor networks is presented in this paper, which takes network homogeneity into account. The modified protocol is the optimum clustering and routing protocol in wireless sensor networks (OCRSN), which simulates an enhanced network coupled node pair model. Our suggested modified approach studies and enhances factors such as network stability, network lifetime, and cluster monitor mechanism choice. The significance of typically combining sensor endpoints is applied to maximize energy efficiency. The proposed protocol significantly improved network parameters in simulations, showing that it could be a valuable option for WSNs. In wireless sensor networks, in addition to memory considerations and dependable transportation, this paper presents a hop-by-hop re-transmission strategy and congestion mitigation, which is the major contribution of this paper. It is a very consistent method based on a pipe flow model. After performing additional optimized overhead to improve the network lifespan of wireless sensors networks, the current algorithm can be paralleled to the less energy adaptive clustering hierarchy protocol. The optimal clustering in multipath and multihop technique intends to minimize the energy consumption highlighted for a circular area enclosed by a sink by replacing one-hop communication with efficient multihop communication. The optimum quantity of clusters is determined, and the energy consumption is reduced by splitting the network into clusters of nearly equal size. The obtained simulation results will demonstrate the increase in the network lifetime compared to previous clustering strategies such as Low Energy Adaptive Clustering Hierarchy.

Doping dependent electronic and magnetic ordering in mixed-valent La1−x Sr x MnO3 thin films

We have investigated the collective electronic and magnetic orderings of a series of La1−x Sr x MnO3 thin films grown epitaxially strained to (001) oriented strontium titanate substrates as a function of doping, x, for 0 ≤ x ≤ 0.4. We find that the ground states of these crystalline thin films are, in general, consistent with that observed in bulk crystals and thin film samples synthesized under a multitude of techniques. Our systematic study, however, reveal subtle features in the temperature dependent electronic transport and magnetization measurements, which presumably arise due to Jahn-Teller type distortions in the lattice for particular doping levels. For the parent compound LaMnO3 (x = 0), we report evidence of a strain-induced ferromagnetic ordering in contrast to the antiferromagnetic ground state found in bulk crystals.

Growth direction dependent separate-channel charge transport in the organic weak charge-transfer co-crystal of anthracene-DTTCNQ.

Co-crystallization is an efficient way of molecular crystal engineering to tune the electronic properties of organic semiconductors. In this work, we synthesized anthracene-4,8-bis(dicyanomethylene)4,8-dihydrobenzo[1,2-b:4,5-b']-dithiophene (DTTCNQ) single crystals as a template to study the crystal growth direction dependent charge transport properties and attempted to elucidate the mechanism by proposing a separate-channel charge transport model. Single-crystal anthracene-DTTCNQ field-effect transistors showed that ambipolar transport properties could be observed in all crystal growth directions. Furthermore, upon changing the measured crystal directions, the electronic properties experienced a weak change from n-type dominated ambipolar, balanced ambipolar, to p-type dominated ambipolar properties. The theoretical calculations at density functional theory (DFT) and higher theory levels suggested that the anthracene-DTTCNQ co-crystal motif was a weak charge-transfer complex, in line with the experiment. Furthermore, the detailed theoretical analysis also indicated that electron or hole transport properties originated from separated channels formed by DTTCNQ or anthracene molecules. We thus proposed a novel separate-channel transport mechanism to support additional theoretical analysis and calculations. The joint experimental and theoretical efforts in this work suggest that the engineering of co-crystallization of weak charge-transfer complexes can be a practical approach for achieving tuneable ambipolar charge transport properties by the rational choice of co-crystal formers.

Safety Climate Assessment: The Implementation of Psychological Fatigue Indicators in Airline Fatigue Risk Management Systems

In commercial aviation, safety is of paramount importance and an indispensable prerequisite for building extensive, dependable air transportation networks. Several aspects affect airline safety, from training to operations and organizational conditions. The critical importance of aircrew fatigue has long been identified; in 2016, nearly 20% of all accidents under investigation by the US NTSB had it listed as one of the probable causes or contributing factors. This study aims to evaluate the utility of adding psychological fatigue elements to the fatigue self-report and survey tools currently used by airlines. Research goals include identifying psychological fatigue markers in airline fatigue survey forms, analyzing these instruments to determine their sensitivity in identifying fatigue that is not exclusively attributed to physiological factors, and investigating potential improvements of these instruments for use in commercial aviation. The authors examined the effect of psychological and physiological fatigue factors on the aviation industry's overall state and dynamics, especially given the consequences of the recent pandemic. Analysis indicates that incorporating psychological items to existing fatigue reporting and survey instruments significantly changes the measured fatigue levels, suggesting that measuring physiological fatigue alone may not be sufficient to accurately determine overall fatigue levels. The proposed implementation of psychological Fatigue Indicators identifies critical and significant risks related to the current Fatigue Risk Management System, especially in atypical periods when the aviation industry is experiencing substantial disruptions and psychological fatigue is prevalent.

Magneto-tunability of photocurrent in Zn0.3Ni0.7Fe2O4/ZnO-rGO composite heterojunction device

We studied light and magnetic field dependent DC transport properties of Zn0.3Ni0.7Fe2O4/ZnO-reduced graphene oxide composite heterojunction. Current through the heterojunction is expected from the carrier injection and tunneling in forward and reverse bias, respectively. Application of magnetic field has shown both negative magnetoresistance (MR) at forward bias and positive MR at reverse bias. The negative MR is attributed to the reduction of spin dependent scattering in the bulk of Zn0.3Ni0.7Fe2O4 layer. On the other hand, under reverse bias, a magnetic field dependent increase of depletion region in Zn0.3Ni0.7Fe2O4 side is supposed to take place, resulting in a positive MR. Under 660 nm visible light illumination, photoresponse has been observed. Under illumination, negative MR is found in reverse bias. This negative MR is expected to be associated with the magnetic field dependent widening of reverse bias depletion region. In forward bias voltages, under strong illumination of 3.08 mW/cm2 of 660 nm light, a positive MR is found. This positive MR is associated with the light dependent enhancement of depletion width at Zn0.3Ni0.7Fe2O4 side under high injection mode. When the applied voltage is swept along a cycle, irreversible nature of I-V characteristics is observed.

Systematic analysis and comparison of ABC proteins superfamily confer structural, functional and evolutionary insights into four cotton species

ATP binding cassette transporters (ABCTs) is one of the largest gene superfamily comprising of integral membrane proteins that are ubiquitously found in all domains of life and implicated in ATP dependent active transport of ligands across the concentration gradient. We present here the identification and distribution of ABC proteins from seven plant species into four groups (Full, Half, Quarter and ABC2 molecules), eight families (ABCA to ABCG and ABCI) and twelve sub families (MDR, PDR, MRP, PMP, AOH, ATH, ATM, TAP, WBC, RLI, GCN and NAP) based on topology, orientation, size, and phylogenetic relationships with main focus on four cotton species especially tetraploid Gossypium hirsutum (Gh) encoding 320 ORFs. Dynamics of complex formation of structurally characterized ABCTs from each subfamily shows their kinetic and molecular mechanisms to combine the ATP hydrolysis and binding for substrate translocation, portraying a "structure to function relationship". Analysis of protein motif and genomic organizations displayed structural and functional conservation within same subfamily but diverged among the different subfamilies. Abundance of small sized single ABCs signifies the higher gene death/birth rate and ongoing evolution for functional advancements and environmental adaptability. Gene duplication relationship analysis illustrates the major role of tandem and segmental duplication in large scale expansion of ABC gene family in mentioned species. The overall Ka/Ks ratio indicated the intense purifying selection of ABC genes in four cotton species during evolution. In addition, tissue specific expression profiling, abiotic stress resistance and Co-expression networking of GhABCs infers their role in diverse range of molecular, cellular and biological processes. Cis-elements and gene enrichments also supported their predicted roles in substrates translocation, xenobiotic detoxification, lipid metabolism, hormonal and abiotic stresses responses. Forward and reverse genetics along with evolutionary trajectories, structural dynamics and validated expression profiling will provide much-needed clarity and a qualitative molecular framework for future research. This study will further broaden our insights into the evolution and functional elucidation of ABC gene family in cotton.