Sudden Increase In Resistance Research Articles

Amorphization transition and electrical properties of La2−xCexCuO4 polycrystalline materials

In contrast to crystals, amorphous materials exhibit distinctive properties and applications due to their unique electronic structure and surface energy. Moreover, the amorphous modification of crystalline materials also results in numerous notable and unique properties. In this study, we propose the amorphous modification of polycrystal La2CuO4 with CeO2, examining the composition of the two phases and changes in the crystal structure. Our findings indicate that the degree of ordering of the La2CuO4 phase significantly decreases as the CeO2 content increases, leading to a resistivity increase in 3–4 orders of magnitude. Furthermore, within the 40–400 K, the transition of the Efros–Shklovskii variable range hopping (E–S VRH) transport mechanism between localized states to the Mott 3D VRH and the crossover around 230 K is observed. The method presented here has great potential in modifying polycrystalline materials by using amorphization to make a sudden increase in resistivity.

Aberrant photoelectric effect in the topological insulator/n-GaN heterojunction (Bi2Te3/n-GaN) under unpolarized illumination.

A topological insulator has a unique graphene-like Dirac cone conducting surface state, which is excellent for broadband absorption and photodetector applications. Experimental investigations on the Bi2Te3/n-GaN heterojunction exhibited an aberrant photoelectric effect under the influence of unpolarized light. Transport measurements of the Bi2Te3/n-GaN heterojunction revealed a negative photoconductance, with a sudden increase in resistance. This was consistent with the applied range of wavelength and power used for incident light while it was contrary to the usual gap-state transition model, which states that a negative conductance is due to the trapping of charge carriers. The observed aberrant photoelectric effect seen in Bi2Te3/n-GaN heterojunction devices was due to the polycrystalline nature of the Bi2Te3 topological insulator film, where the incident photon-induced bandgap in the Dirac cone surface state resulted in a negative photoelectric effect. This phenomenon opens the possibility for applications in highly sensitive photodetectors and non-volatile memories, along with employing the bandgap-opening concept in retinomorphic devices.

Quinolines and Macrolides Resistance-Associated Mutations in Chlamydia trachomatis in Women Endocervical Samples in the West Region of Cameroon


 
 
 
 Chlamydia trachomatis infection is a public health problem worldwide. Although antibiotic resistance of this strict intracellular bacterium is rare, it is important to monitor the appearance of resistance genes to available efficient antibiotics. This study aimed to screen for mutations in some of these genes in C. trachomatis clinical isolates, which may be associated to resistance to quinolone and macrolide antibiotics. Thirty-five endocervical samples were collected from women aged between 18 and 49 in five district hospitals in the Western Region of Cameroon. The mutations in quinolones (parC and gyrA) and macrolides (L4, L22 and 23S rRNA) resistance domains were detected by PCR followed by sequencing on positive samples to C. trachomatis. The overall mutation rate for the studied genes was 60% in the studied samples. Seven (20%) and twelve (34%) samples presented mutations in the parC and gyrA gene respectively. Mutations in L4 (11.42%) and L22 (60%) were detected in ours samples, while no mutation was found in 23S rRNA gene. Seven clinical samples (20%) presented mutations to both macrolide and quinolone resistance genes. This study revealed a relatively high rate of mutations in the resistance genes to macrolides and quinolones in C. trachomatis in the West Cameroon. This rate of mutation calls for the competent authorities for better surveillance of C. trachomatis infection in West Cameroon to avoid a sudden increase in resistance to antibiotics in the years to come.
 
 
 
 

Damage Evolution of Sandstone under Constant‐Amplitude Cyclic Loading Based on Acoustic Emission Parameters and Resistivity

In the real environment, besides static load, rock is more affected by cyclic load. There is a large difference in the mechanical properties exhibited by rocks under cyclic and static loading. Therefore, it is particularly necessary to investigate the mechanical characteristics of rock subjected to cyclic loading. These parameters of rock, acoustic emission (AE) and resistivity, are both sensitive to the failure process of rock, and they are complementary to the different stages of rock damage. Therefore, in this paper, the AE characteristics and resistivity properties of sandstone subjected to constant‐amplitude cyclic loading and unloading were experimentally investigated using a typical sandstone in Chongqing. The same three‐stage pattern was found for the AE evolution of sandstones during constant‐amplitude cyclic loading. Initial evolution stage: the rock deformation is fast with strong changes in the AE signal. The rock deformation developed slowly while the changes of the AE signal were stable in the constant velocity evolution stage. The rock deformation developed dramatically while the AE signal became more intense in accelerated evolution stage. The change in resistivity is characterized by a rapid decrease during the loading stage and a rapid rebound during the unloading stage. Overall, from the beginning of the cycle to the end of the cycle, the resistivity of the sandstone showed a general trend of gradual decrease, until the sudden increase in resistivity at the time of damage. Finally, a damage model based on AE parameters and resistivity was constructed by combining damage mechanics.

Role of disorder and strong 5d electron correlation in the electronic structure of Sr2TiIrO6

Transport and magnetic properties along with a high-resolution valence band photoemission study of disordered double perovskite Sr2TiIrO6have been investigated. The insulator to insulator transition along with a magnetic transition concurrently occur at 240 K. The comparison of the valence band photoemission with band structure calculations suggests that the spin orbit coupling as well as the electron correlation are necessary to capture the line shape and width of the Ir 5d band. Room temperature valence band photoemission spectra show a negligibly small intensity at the Fermi energy, EF. A Fermi cut-off is observed at low temperatures employing high resolution. The spectral density of states at room temperature exhibits energy dependence signifying the role of electron-electron interaction. This energy dependence changes to below the magnetic transition evidencing the role of the electron-magnon coupling in a magnetically ordered state. The evolution of a pseudogap () explains the sudden increase in resistivity below 50 K in this disordered system. The temperature-dependent spectral density of states at EF exhibiting behaviour verifies the Altshuler-Aronov theory for correlated disordered systems.

Electromigration Characteristics and Morphological Evolution of Cu Interconnects on CVD Co and Ru Liners for 10-nm Class VLSI Technology

Ruthenium (Ru) and cobalt (Co) are new candidates for the replacement of physical vapor deposition tantalum (Ta) in liner materials because Ru and Co have excellent Cu-filling properties when deposited using chemical vapor deposition (CVD). Under accelerated current stressing conditions, Cu interconnects on a TaN/Co barrier showed an abrupt increase in resistance. The Cu resistance on a TaN/Ru barrier increased gradually and saturated with low deviation because voids generated randomly, and the Cu that remained on the Ru in the voids acted as shunt layers, preventing a sudden increase in resistance. Cu evolution tests on a Ru liner indicated that Cu had a strong bond with CVD Ru liner, even at high temperatures. These results suggest that Cu deposited on a TaN/Ru barrier can endure electromigration failure.

Effect of magnetic field on electronic transport in a bilayer graphene nanomesh

We report on the observation of an unexpected sudden increase of resistance in bilayer graphene nanomesh (GNM) in the temperature range 270 ∼ 300 K that is strongly dependent on the magnetic field strength. We conjecture that the sharp increase in resistance originates from ripple scattering as induced by substrate roughness. The observed result is evidence of extrinsic corrugation in bilayer GNM as an additional scattering source that contributes to significant resistance. The observed weak localization in the GNM indicates intervalley scattering induced by lattice defects acts as resonant scatterers attribute to the high D peak. Magnetotransport measurement strongly supports that the charge inhomogeneity related to the intrinsic disorder in bilayer GNM and the positive magnetoresistance shows a linear behavior with magnetic field strength. Potentially, the observed phenomena, therefore, point to a clear pathway towards practical application of bilayer GNM and to the design of a graphene magnetic sensor that can be manipulated by a magnetic field and a new generation of spintronics.

Water absorption test for carbon fiber epoxy resin composite based on electrical resistance

Electric contacts were inserted into a carbon fiber epoxy resin composite to research the relationship between water absorption and resistance, which allowed the diagnosis of composite water absorption in a nondestructive way. The results show that the carbon fiber in the composite form does not absorb water from the environment, and its resistance remained unchanged when immersed in water. However, the resistance of the composite increased after water was absorbed along the fiber until the specimen reached saturation, which resulted in a sudden increase in resistance. The transverse resistance changed logarithmically in relation to water absorption. The data fitting equation is y = 2.03 × lg(x)−6.26 (R2 = 0.98), where x is the transverse resistance after water absorption (Ω), and y is the weight gain rate after water absorption (%). According to this equation, the weight gain rate of the composite can be calculated from the transverse resistance.

Synergistic effect of electromigration and Joule heating on system level weak-link failure in 2.5D integrated circuits

In system level electromigration test of 2.5D integrated circuits, a failure mode due to synergistic effect of Joule heating and electromigration has been found. In the test circuit, there are three levels of solder joints, two Si chips (one of them has through-Si-via), and one polymer substrate. In addition, there are two redistribution layers; one between every two levels of solder joints. We found that the redistribution layer between the flip chip solder joints and micro-bumps is the weak-link and failed easily by burn-out in electromigration test. The failure is time-dependent with sudden resistance increase. Preliminary simulation results show that Joule heating has a positive feedback to electromigration in the redistribution layer and caused the thermal run-away failure. Joule heating becomes an important reliability issue in the future scaling of semiconductor devices.

Impact Of Strain In Drawing Process And Surface Modification On Resistance To Electrochemical Corrosion Of Wires Used In Dentistry

Abstract The study presents the results of research into the impact of strain in cold drawing and surface modification treatment on corrosion properties of wires made of X10CrNi 18-8 steel used in maxillofacial surgery. Scanning microscopy enabled to make images of the surface of wires after drawing process as well as after surface modification treatment. Resistance to electrochemical corrosion was evaluated on the ground of registered anodic polarisation curves in artificial saliva. In order to evaluate physical and chemical properties of the surface, electrochemical impedance spectroscopy was performed. Test results show deterioration of corrosion properties of wires along with strain taking place in drawing process. It was proved that electrochemical polishing and chemical passivation caused sudden increase of resistance of wires made of stainless steel to pitting corrosion in artificial saliva.

Enhancement of the transport and dielectric properties of graphite oxide nanoplatelets‐polyvinyl alcohol composite showing low percolation threshold

AbstractGraphite oxide nanoplatelets (GOnP) were prepared using standard method and used to make GOnP‐polyvinyl alcohol (PVA) composites by using solution cast technique. Significant enhancement of electrical conductivity and dielectric permittivity of the GOnP/PVA composites are observed at low GOnP concentration (fGOnP = fc∼0.41 vol%) which is the percolation threshold value estimated from the concentration dependent transport and dielectric data. Nearly 300 times increase in dielectric permittivity (compared with that of PVA) is observed in the GOnP/PVA composite around fc. We notice interesting metal‐insulator like transition (a sudden increase in resistivity) from the temperature dependent resistivity data in the pure GOnP sample around TMI ∼ 275 K which is shifted to 300 K in the GOnP/PVA composite for fc = 0.41 vol%, indicating drastic change of sp3/sp2 ratio around respective TMI. The present graphite‐based composite material might be processed for different applications. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Single-valley quantum Hall ferromagnet in a dilute MgxZn1−xO/ZnO strongly correlated two-dimensional electron system

We investigate the spin susceptibility (${g}^{*}$${m}^{*}$) of dilute two-dimensional (2D) electrons confined at the Mg${}_{x}$Zn${}_{1\ensuremath{-}x}$O/ZnO heterointerface. Magnetotransport measurements show a four-fold enhancement of ${g}^{*}$${m}^{*}$, dominated by the increase in the Land\'e $g$-factor. The $g$-factor enhancement leads to a ferromagnetic instability of the electron gas as evidenced by sharp resistance spikes. At high magnetic field, the large ${g}^{*}$${m}^{*}$ leads to full spin polarization, where we found sudden increase in resistance around the filling factors of half-integer, accompanied by complete disappearance of fractional quantum Hall (QH) states. Along with its large effective mass and the high electron mobility, our result indicates that the ZnO 2D system is ideal for investigating the effect of electron correlations in the QH regime.

Multiband transport in bilayer graphene at high carrier densities

We report a multiband transport study of bilayer graphene at high carrier densities. Employing a poly(ethylene)oxide-CsClO$_4$ solid polymer electrolyte gate we demonstrate the filling of the high energy subbands in bilayer graphene samples at carrier densities $|n|\geq2.4\times 10^{13}$ cm$^{-2}$. We observe a sudden increase of resistance and the onset of a second family of Shubnikov de Haas (SdH) oscillations as these high energy subbands are populated. From simultaneous Hall and magnetoresistance measurements together with SdH oscillations in the multiband conduction regime, we deduce the carrier densities and mobilities for the higher energy bands separately and find the mobilities to be at least a factor of two higher than those in the low energy bands.

Experimental Methods to Detect and Quantify Damage in Restrained Concrete Ring Specimens

This paper describes the use of three experimental methods to detect shrinkage cracking in restrained ring specimens. These methods include monitoring the strain at the inner surface of the restraining steel ring, using passive acoustic emission, and measuring the electrical resistance of conductive materials that are applied to the surface of the mortar. The methods for detecting cracking are compared and their advantages and limitations are discussed. Both plain and steel fiber reinforced (2% steel fiber by volume) mortar were evaluated in this study. The time of through cracking detected by the three methods corresponds to the time of visible cracking. In the mixtures containing fibers the time of through cracking is delayed significantly when compared to the plain systems. The delay in the age of through cracking can be explained by the role of fibers in arresting the cracks as they develop and their role in transferring stress across the crack width that keeps the cracks from opening. The passive acoustic emission data indicates substantial damage development before a through crack forms. The time of through cracking can be detected using conductive surfaces with a sudden increase in resistance of these conductive elements. Cracking can be detected using conductive coatings when the crack is 0.02 mm or larger. Specimens with different degrees of restraint show through cracking at approximately the same stress level; however, the age at which cracking occurs decreases as the degree of restraint increases. This can be attributed to the increased micro-cracking (i.e., damage and precritical crack growth) as confirmed with acoustic emission data.

Emergence of multiple drug resistance Vibrio cholerae O1 in East Delhi

Considering the changing geographical and temporal occurrence of Vibrio cholerae, there is a continuing need to monitor the strain characteristics and antibiotic resistance patterns of this pathogen. The present study was conducted to document the changing biology of V. cholerae isolates in and around Delhi, India, and the development of antibiotic resistance. A total of 1,424 stool samples or rectal swabs from patients with acute secretory diarrhoea admitted to Guru Teg Bahadur Hospital, Delhi, between January 2007 and December 2009 were processed using standard bacteriological methods. Strains identified as V. cholerae were further subjected to serogrouping, phage typing and antimicrobial susceptibility testing. Minimum inhibitory concentration (MIC) of gentamicin and tetracycline was determined. V. cholerae was isolated in 242/1,424 (17.0%) specimens. Of these, the majority were V. cholerae O1 serotype (98.3%) and serovar Ogawa. The drugs to which V. cholerae O1 isolates showed high levels of resistance were nalidixic acid, furazolidone, and cotrimoxazole throughout the study period, whereas strains were usually susceptible to chloramphenicol and cefotaxime. In 2007, there was a sudden increase of resistance to gentamicin and tetracycline, followed by a slow reversal to previous levels in subsequent years. The phage typing pattern (Basu and Mukherjee scheme) showed a dominance of phage type 2 throughout the study period. The importance of reporting all cases of V. cholerae, should be greatly emphasized, with the ultimate goal of understanding the constantly changing resistance patterns of this pathogen.

High pressure electrical resistivity studies on Ni-doped TiO 2 nanoparticles

Electrical resistivity measurement of Ni-doped TiO 2 nanoparticles were performed under high pressure using a Bridgman opposed anvil setup. It is observed that, anatase phase nanoparticles shows a sudden increase in resistivity below the pressure limit of 4 GPa and is attributed to the transition from anatase to rutile phase. In addition, the transition limit is shifted towards lower pressure region with increase in dopant concentration. But, Ni-doped TiO 2 nanoparticles with rutile phase shows a rapid decrease in resistivity up to 5 GPa and thereafter it becomes constant. Samples with constant resistivity behavior are mainly ascribed to the semiconductor-metallic transformation.

Theory ofI−Vcharacteristics of magnetic Josephson junctions

We analyze the electrical characteristics of a circuit consisting of a free thin-film magnetic layer and source and drain electrodes that have opposite magnetization orientations along the free magnet's two hard directions. We find that when the circuit's current exceeds a critical value there is a sudden resistance increase which can be large in relative terms if the currents to source or drain are strongly spin polarized and the free magnet is thin. This behavior can be partly understood in terms of a close analogy between the magnetic circuit and a Josephson junction.

Transition from a weak ferromagnetic insulator to an exchange-enhanced paramagnetic metal in theBaIrO3polytypes

As a follow-up of the high-pressure synthesis and the structural determination of two new ${\text{BaIrO}}_{3}$ polytypes, we report in this paper a systematic study of the physical properties of all polytypes available to us through measurements of magnetic, electronic transport, thermodynamic, and low-temperature structural as well as pressure effects. With increasing fraction of the corner- to face-sharing octahedra in the sequence $9R$ $(hhChhChhC)\ensuremath{\rightarrow}5H(hChCC)\ensuremath{\rightarrow}6H(hCChCC)$, the ground states of ${\text{BaIrO}}_{3}$ evolve from a ferromagnetic insulator with ${T}_{\text{c}}\ensuremath{\approx}180\text{ }\text{K}$ in the $9R$ phase to a ferromagnetic metal with ${T}_{\text{c}}\ensuremath{\approx}50\text{ }\text{K}$ in the $5H$ phase, and finally to an exchange-enhanced paramagnetic metal near a quantum critical point (QCP) in the $6H$ phase. The experimental results for the $9R$ phase confirm that the ferromagnetic transition is accompanied by a lattice instability, presumably associated with the formation of a charge density wave. The evidence includes a sudden increase in resistivity and thermoelectric power, an anomaly in the thermal conductivity, an unusual expansion of the $c$ axis, and an extraordinarily large pressure coefficient of ${T}_{\text{c}}$. In contrast, the ferromagnetic transition in the $5H$ ${\text{BaIrO}}_{3}$ only gives rise to weak anomalies in the resistivity and specific heat near ${T}_{\text{c}}$, similar to ${\text{SrRuO}}_{3}$; the $5H$ phase is the first weak ferromagnetic metal among the known oxide iridates. The $6H$ phase remains a paramagnetic metal to the lowest temperature. However, a strongly enhanced thermoelectric power and a non-Fermi-liquid behavior from the resistivity measurement at low temperature show that quantum critical fluctuations play a role in this exchange-enhanced paramagnetic phase. A positive thermoelectric power confirms the charge carriers are holelike for all polytypes, which is consistent with the electronic configuration of Ir(IV) $(5{d}^{5})$ in the low-spin state. The low-temperature specific-heat coefficients and Sommerfeld-Wilson ratios are in agreement with the evolution of the ground states across a ferromagnetic to paramagnetic QCP.

Acute cor pulmonale

Acute cor pulmonale is a form of acute right heart failure produced by a sudden increase in resistance to blood flow in the pulmonary circulation, which is now rapidly recognized by bedside echocardiography. In the clinical setting, acute cor pulmonale is mainly observed as a complication of massive pulmonary embolism or acute respiratory distress syndrome. In acute respiratory distress syndrome, the worsening effect of mechanical ventilation has been recently emphasized. As a general rule, the treatment consists in rapidly reducing resistance to blood flow in the pulmonary circulation, obtained by a specific strategy according to etiology.

Effect of A-site dopant on the piezoresistive characteristics of La0.8Sr0.2MnO3 ceramics

This letter reports the effect of the A-site doping (2, 4, and 6 mol% Bi and Li) on the piezoresistance phenomenon in La0.8Sr0.2MnO3 (LSMO) polycrystalline ceramics. The fractional change in resistivity was found to be nominal for Li-modified samples but samples modified with 4 and 6 mol% Bi2O3 exhibited 1.8% and 2.3% fractional change in resistivity $$ [(\rho _{o} - \rho _{\sigma } )/\rho _{o} ] $$ at 19.2 MPa which is significantly higher than that for pure LSMO. The enhancement in piezoresistive phenomenon is attributed to distortion of Mn–O bond due to substitution of smaller ion on to La-site. All the samples showed a sudden increase in resistivity with applied stress in the range of 0.5–2 MPa and the behavior was found to saturate as the magnitude of applied stress increases. Magnetic measurements as a function of field and temperature were conducted to confirm the A-site substitution.