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Experiments were initiated to characterize a waterhemp population (CHR) discovered in a central Illinois corn field after it was not controlled by the 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor topramezone. Field experim...
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Experiments were initiated to characterize a waterhemp population (CHR) discovered in a central Illinois corn field after it was not controlled by the 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor topramezone. Field experiments conducted during 2014-2015 indicated that acetolactate synthase (ALS)-, protoporphyrinogen oxidase (PPO)-, photosystem II (PSII)-, and HPPD-inhibiting herbicides and the synthetic auxin 2,4-D did not control the CHR population. Laboratory experiments confirmed target site-based resistance mechanisms to ALS- and PPO-inhibiting herbicides. Herbicide doses required to reduce dry biomass 50% (GR(50)) were determined in greenhouse dose-response experiments, and indicated 16-fold resistance to the HPPD inhibitor mesotrione, 9.5-fold resistance to the synthetic auxin 2,4-D, and 252-fold resistance to the PSII inhibitor atrazine. Complementary results from field, laboratory, and greenhouse investigations indicate that the CHR population has evolved resistance to herbicides from five sites of action (SOAs): ALS-, PPO-, PSII-, and HPPD-inhibiting herbicides and 2,4-D. Herbicide use history for the field in which CHR was discovered indicates no previous use of 2,4-D.
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The study of resistance has exploded during recent years and the field has broadened in order to accommodate more issues. The broadened scope of resistance studies is fruitful, yet the embracing of resistance's complex character h...
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The study of resistance has exploded during recent years and the field has broadened in order to accommodate more issues. The broadened scope of resistance studies is fruitful, yet the embracing of resistance's complex character has led to a situation where the current research on resistance does not offer the appropriate tools to analyze the multiple and often overlapping forms of resistance. It is in this scholarly context that this paper form a bridge between fields in its endeavor to illuminate the richness of 'resistance', while still providing tools - for example, definitions, paths and forms of resistance - for analyzing it.
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The tedizolid MIC of 27 clinical isolates of linezolid-resistant staphylococci and enterococci was determined. Tedizolid MICs were >= 1 mu g/mL and were 4- to 32 -fold lower than those of linezolid. Linezolid resistance mechanisms...
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The tedizolid MIC of 27 clinical isolates of linezolid-resistant staphylococci and enterococci was determined. Tedizolid MICs were >= 1 mu g/mL and were 4- to 32 -fold lower than those of linezolid. Linezolid resistance mechanisms included G2576T 235 rRNA gene and rplC and rplD mutations. (C) 2016 Elsevier Inc. All rights reserved.
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Accurate extraction of parasitic gate (R_G). source (R_S), drain (R_D), and substrate (R_(sub)) resistances in MOSFETs is important in the modeling and characterization for DC and RF applications. Combining DC current-voltage and ...
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Accurate extraction of parasitic gate (R_G). source (R_S), drain (R_D), and substrate (R_(sub)) resistances in MOSFETs is important in the modeling and characterization for DC and RF applications. Combining DC current-voltage and low-frequency capacitance-voltage characteristics with an equivalent circuit, we report a simple technique for a complete and separate extraction of parasitic resistances (R_G, R_S. R_D. and R_(sub)) in individual MOSFETs without employing multiple devices or complicated S-parameter characterization with various device combinations. Intrinsic spreading component is also separated from the contact-related extrinsic component in R_S and R_D.
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A greater number of, and more varied, modes of resistance have evolved in weeds than in other pests because the usage of herbicides is far more extensive than the usage of other pesticides, and because weed seed output is so great...
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A greater number of, and more varied, modes of resistance have evolved in weeds than in other pests because the usage of herbicides is far more extensive than the usage of other pesticides, and because weed seed output is so great. The discovery and development of selective herbicides are more problematic than those of insecticides and fungicides, as these must only differentiate between plant and insect or pathogen. Herbicides are typically selective between plants, meaning that before deployment there are already some crops possessing natural herbicide resistance that weeds could evolve. The concepts of the evolution of resistance and the mechanisms of delaying resistance have evolved as nature has continually evolved new types of resistance. Major gene target-site mutations were the first types to evolve, with initial consideration devoted mainly to them, but slowly 'creeping' resistance, gradually accruing increasing levels of resistance, has become a major force owing to an incremental accumulation of genetic changes in weed populations. Weeds have evolved mechanisms unknown even in antibiotic as well as other drug and pesticide resistances. It is even possible that cases of epigenetic 'remembered' resistances may have appeared.
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In 2006 and 2007, farmers from two counties in Illinois reported failure to control waterhemp with glyphosate. Subsequent onsite field experiments revealed that the populations might be resistant to multiple herbicides. Greenhouse...
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In 2006 and 2007, farmers from two counties in Illinois reported failure to control waterhemp with glyphosate. Subsequent onsite field experiments revealed that the populations might be resistant to multiple herbicides. Greenhouse experiments therefore were conducted to confirm glyphosate resistance, and to test for multiple resistance to other herbicides, including atrazine, acifluorfen, lactofen, and imazamox. In glyphosate dose-response experiments, both populations responded similarly to a previously characterized glyphosate-resistant population (MO1). Both Illinois populations also demonstrated high frequencies of resistance to the acetolactate synthase (ALS) inhibitor, imazamox. Additionally, one of the populations demonstrated high frequencies of resistance to both atrazine and the protoporphyrinogen oxidase (PPO) inhibitor, lactofen. Furthermore, using combinations of sequential and tank-mix herbicide applications, individual plants resistant to herbicides spanning all four site-of-action groups were identified from one population. Molecular experiments were performed to provide an initial characterization of the resistance mechanisms and to provide confirmation of the presence of multiple resistance traits within the two populations. Both populations contained the W574L ALS mutation and the Delta G210 PPO mutation, previously shown to confer resistance to ALS and PPO inhibitors, respectively. Atrazine resistance in both populations is suspected to be metabolism-based, because a triazine target-site mutation was not identified. A P106S EPSPS mutation, previously reported to confer glyphosate resistance, was identified in one population. This mutation was identified in both resistant and sensitive plants from the population; however, and so more research is needed to determine the glyphosate-resistance mechanism(s). This is the first known case of a weed population in the United States possessing multiple resistance to herbicides from four site-of-action groups.
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Herbicide-resistant weed biotypes are an increasing problem in agriculture, with reports of resitance to almost every herbicide class at some place in the world, and the total number of resistant biotypes at over 250. Agricultural...
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Herbicide-resistant weed biotypes are an increasing problem in agriculture, with reports of resitance to almost every herbicide class at some place in the world, and the total number of resistant biotypes at over 250. Agricultural Research Service (ARS) scientists have been key players in this area since the first substantiated occurence of these resistance biotpes in the 1970s. The most significant of their contributions is the complete unraveling of the mechanism of triazine resistance by Arntzen and colleagues, then with ARS at the University of Illinois. These studies established a hig h banchmark for research in this area and are a model for all studies in this area. Other ARS scientists have investigated a large number of weed biotypes with resistance to a wide range of herbicide classes and mechanisms of resistance. Collectively, these studies have been used to generate herbicide resistance-management schemes for growners, based uon the herbicide site and the potential for resistance development.
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This study systematically investigates the effects of electrical resistance at the workpiece/electrode interface or electrode face on temperature dependent dynamic resistance during resistance spot welding (RSW). To evaluate tempe...
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This study systematically investigates the effects of electrical resistance at the workpiece/electrode interface or electrode face on temperature dependent dynamic resistance during resistance spot welding (RSW). To evaluate temperature transport equations of mass, momentum, energy, species and magnetic field intensity in workpieces, the energy and magnetic equations in the electrode are solved. Contact resistances composed of constriction and film resistances are functions of hardness, temperature, electrode force and surface conditions. The results show that dynamic resistance is complicated due to different variations of film and constriction resistances with temperature at not only the faying surface but also the electrode face in the early stage, i.e. shorter than around 3 cycles. Dynamic resistance in this stage is fortunately insignificant to transport processes. When the power is off, dynamic resistance depends on competition between decreased bulk resistance and increased constriction resistance at the electrode face. Decreased constriction resistance at the electrode face reduces dynamic resistance and temperature.
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In the geophysical electrical resistivity method, arrays of electrodes are commonly deployed on the Earth's surface. In electrical power engineering applications, arrays of electrodes are often connected in parallel in order to re...
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In the geophysical electrical resistivity method, arrays of electrodes are commonly deployed on the Earth's surface. In electrical power engineering applications, arrays of electrodes are often connected in parallel in order to reduce the total resistance to ground. The electrical characteristics of an array of N electrodes can be fully described by N self-resistances and N(N-1)/2 mutual resistances for a total of N(N+1)/2 independent parameters which represent the coefficients of an N by N symmetric matrix. Typically, certain linear combinations of the mutual resistances are measured during a geophysical electrical resistivity survey while protocols of specific measurements are used to determine self-resistances. In this contribution, I investigate whether it is possible to determine all of the self- and mutual resistances for an array and hence capture all possible information. I assume that measurements of potential and current can be made at each electrode and that any combination of series and parallel current injections between the electrodes can be made. I show that all N(N+1)/2 resistances can only be determined uniquely if current and voltage reference electrodes that are external to the array are used. If only an external current electrode or only an external voltage reference is used then only N(N+1)/2-1 independent measurements can be made and the system is underdetermined. If only electrodes within the array itself are available only, N(N-1)/2 independent measurements can be made and the system is strongly underdetermined. The procedure outlined here also gives a general prescription for calculating the completeness and redundancy of any given array.
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Current increases in antifungal drug resistance in Candida spp. and clinical treatment failures are of concern, as invasive candidiasis is a significant cause of mortality in intensive care units (ICUs). This trend reflects the la...
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Current increases in antifungal drug resistance in Candida spp. and clinical treatment failures are of concern, as invasive candidiasis is a significant cause of mortality in intensive care units (ICUs). This trend reflects the large and expanding use of newer broad-spectrum antifungal agents, such as triazoles and echinocandins. In this review, we firstly present an overview of the mechanisms of action of the drugs and of resistance in pathogenic yeasts, subsequently focusing on recent changes in the epidemiology of antifungal resistance in ICU. Then, we emphasize the clinical impacts of these current trends. The emergence of clinical treatment failures due to resistant isolates is described. We also consider the clinical usefulness of recent advances in the interpretation of antifungal susceptibility testing and in molecular detection of the mutations underlying acquired resistance. We pay particular attention to practical issues relating to ICU patient management, taking into account the growing threat of antifungal drug resistance.
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