The antiferromagnetic ground state of copper oxide Mott insulators is achieved by localizing an electron at each copper atom in real space (r-space). Removing a small fraction of these electrons ...(hole doping) transforms this system into a superconducting fluid of delocalized Cooper pairs in momentum space (k-space). During this transformation, two distinctive classes of electronic excitations appear. At high energies, the mysterious 'pseudogap' excitations are found, whereas, at lower energies, Bogoliubov quasi-particles-the excitations resulting from the breaking of Cooper pairs-should exist. To explore this transformation, and to identify the two excitation types, we have imaged the electronic structure of Bi(2)Sr(2)CaCu(2)O(8+delta) in r-space and k-space simultaneously. We find that although the low-energy excitations are indeed Bogoliubov quasi-particles, they occupy only a restricted region of k-space that shrinks rapidly with diminishing hole density. Concomitantly, spectral weight is transferred to higher energy r-space states that lack the characteristics of excitations from delocalized Cooper pairs. Instead, these states break translational and rotational symmetries locally at the atomic scale in an energy-independent way. We demonstrate that these unusual r-space excitations are, in fact, the pseudogap states. Thus, as the Mott insulating state is approached by decreasing the hole density, the delocalized Cooper pairs vanish from k-space, to be replaced by locally translational- and rotational-symmetry-breaking pseudogap states in r-space.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Microorganisms alter gene and protein expression in response to environmental conditions to adapt and survive. Whereas the genetic composition of a microbe represents an organism's biological ...potential, the proteins expressed provide a functional readout of the organism's response to the environment. Understanding protein expression patterns in response to specific environmental conditions furthers fundamental knowledge about a microbe, which can be especially useful for understudied organisms such as Clostridium botulinum examined herein. In addition, protein expression patterns that reproducibly occur in certain growth conditions hold potential in fields such as microbial forensics, in which determination of conditions in which an unknown possible biothreat sample had been grown may be important. To investigate the identity and reproducibility of protein profile patterns for varied strains, we defined the proteomic profiles of four Group I strains of Clostridium botulinum, a Category A biothreat agent and the organism responsible for the production of the botulinum neurotoxin (BoNT), in two different culture media grown for five days. The four C. botulinum strains produced one of three neurotoxins (BoNT/A, /B, or /F), and their protein profiles were compared to that of a fifth non-toxigenic strain of C. sporogenes. These strains each had DNA sequences available to assist in accurate protein identification. Differing culture growth phase, bacterial strain, and growth medium resulted in reproducible protein profiles, which were used to calculate relative protein abundance ratios as an internally normalized metric of microbial growth in varying conditions. The resulting protein profiles provide functional information about how four Group I C. botulinum strains and a C. sporogenes strain respond to the culture environment during growth and explores the feasibility of using these proteins to characterize unknown samples.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Human activities within the riparian zone can alter abiotic properties of a watershed, potentially resulting in abiotic conditions that are stressful for resident fishes. The inability of fish to ...cope physiologically with stressful abiotic conditions can have deleterious effects on individuals, and could potentially lead to population declines or changes to community structure (biodiversity). Defining links between landscape-level processes and performance of individual stream fishes can therefore improve our ability to predict how land use changes can impact stream communities, which has relevance for management activities. This study tested the hypothesis that land use at the watershed scale influences the physiological stress response of resident fishes. For this, replicate streams in agricultural watersheds and forested watersheds were identified; sampling demonstrated that streams in agricultural watersheds were warmer and more thermally variable than streams from agricultural areas. Creek chub from each land use type were sampled for blood and muscle in the field, following exposure to thermal and oxygen stressors in the laboratory, and after prolonged holding at elevated temperatures that replicated field conditions. No differences in baseline physiological parameters were found in fish sampled directly from streams. However, when exposed to low oxygen and high temperature conditions in the laboratory, creek chub from streams within agricultural areas maintained physiological performance with a reduced stress response relative to creek chubs from streams within forested watersheds. In addition, prolonged holding at high temperature removed landscape-level differences in stress responses, resulting in improved physiological performance for all fishes after a heat challenge. Results indicate that creek chub have the ability to adjust physiological responses to improve performance in disturbed environments, and also provide a novel mechanism by which landscape-level processes can influence biodiversity.
Clove oil has become a popular fish anaesthetic for invasive fisheries research procedures, but few studies have examined the use of low concentrations of clove oil to achieve sedation for ...aquaculture procedures such as fish handling and transport. In this study, we used largemouth bass as a model species to examine the behavioral and physiological responses of fish to a gradation of clove oil concentrations (0 to 20 mg l
−1) while exposed to truck transport. Concentrations of clove oil ranging from ∼5 to 9 mg l
−1 elicited a sedative effect resulting in loss of reactivity and reduced cardiac output while maintaining equilibrium. Fish sedated by 5 to 9 mg l
−1 clove oil achieved that level of anaesthetization rapidly and recovered behaviorally more quickly than at higher concentrations. During transportation, videography revealed that fish in deep sedation (stage 2 induction) experienced the least opportunity for physical damage from the tank or conspecifics and had reduced activity relative to other concentrations. Cardiovascular assessments indicated that when exposed to clove oil of any concentration, cardiac output and heart rate rose following an initial bradycardia. Fish exposed to low levels of clove oil recovered rapidly when returned to fresh water, but those exposed to higher concentrations (usually stage 4 or 5 induction) exhibited protracted cardiovascular recovery. Recovery occurred more rapidly for fish that were exposed to stage 2 anaesthesia than nonanaesthetized controls. Low levels of clove oil (5 to 9 mg l
−1) yielded rapid induction and maintenance of stage 2 anaesthesia in subadult largemouth bass and was effective for mitigating the effects of fish transport stress. The results from this study could be useful for aquaculturists and other handling related husbandry practices that require sedation of fish.
We examined the effects of adult common carp (Cyprinus carpio) on shallow aquatic ecosystems and compared the effects with those of a native benthic fish, channel catfish (Ictalurus punctatus). ...Experimental ponds contained enclosures (0.06 ha) with a low carp biomass (174 kg·ha
1
), high carp biomass (476 kg·ha
1
), high catfish biomass (416 kg·ha
1
), and no fish. We measured abiotic factors (turbidity, suspended solids, total phosphorus), as well as effects on adjacent trophic levels (aquatic macrophytes, zooplankton, and aquatic macroinvertebrates) from July to September. Common carp was positively related to total phosphorus, turbidity, suspended solids, and zooplankton biomass, and negatively related to macrophyte and macroinvertebrate abundance. Suspended solids in the carp treatments consisted primarily of inorganic particles. Carp were either positively or negatively related to phytoplankton, depending on zooplankton abundance. A high biomass of carp had greater effect on nutrients, turbidity, and suspended solids than a low biomass. Channel catfish was positively related to total phosphorus concentrations and altered zooplankton composition, but did not affect turbidity, suspended solids, macroinvertebrates, and macrophytes. These results suggest that common carp have a stronger influence on water quality and aquatic community structure than benthic fish native to North America.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Channel catfish Ictalurus punctatus is a highly mobile species and is known to make extensive seasonal movements in lotic systems. Dams have been suggested to detrimentally affect this species, ...although abundant channel catfish populations are known to occur in many fragmented rivers. To examine factors that allow channel catfish to persist in impounded rivers, we assessed relative abundance of channel catfish in three impounded and three flowing sites of the Fox River, Illinois, USA. Radiotelemetry was used to determine movement and habitat use patterns of channel catfish among flowing and impounded areas. Relative abundance of channel catfish was consistently higher at flowing sites than at impounded sites during summer. Several radio‐tagged channel catfish moved downstream into impounded areas in fall, and all tagged individuals were found in impounded areas during winter. The majority of tagged channel catfish moved upstream into flowing areas during spring. Channel catfish used a wide range of depths (0.28–2.60 m), and were always found in current velocities less than 0.50 m s−1. They selected most strongly for coarse substrates, but were infrequently found near cover. Although low‐head dams restrict the movements of channel catfish, impounded areas appear to provide overwintering habitats that may eliminate the need for seasonal long‐distance movements. Small run‐of‐river impoundments, however, may contain unsuitable conditions for channel catfish during other seasons.
Temperature and oxygen gradients exist in nearly every water body, but anthropogenic activities can subject fish to rapid changes in these important environmental variables. These rapid changes in ...temperature and oxygen (generally referred to as temperature or oxygen shock) may have sub-lethal consequences depending upon the magnitude and the fish species. This study quantified physiological changes in largemouth bass, Micropterus salmoides (Lacepède), exposed to two levels of heat and cold shocks and to two levels of hypoxic and hyperoxic shocks. Following a cold shock from 20 °C to 8 °C, plasma cortisol and glucose increased after 1 h and lactate dehydrogenase activity increased after 6 h. Plasma glucose and K⁺ concentrations increased 1 h after a heat shock from 20 °C to 32 °C but not after 6 h. Bass subjected to a hypoxic shock from 8 to 2 mg O₂ L⁻¹ showed decreased plasma K⁺ and increased plasma glucose and white muscle lactate. No changes in physiological parameters were observed in bass subjected up to 18 mg O₂ L⁻¹ hyperoxia. Results from this study suggest that largemouth bass can tolerate a wide range of temperature and oxygen shocks, but temperature decreases of 20 to 8 °C and hypoxia as low as 4 mg O₂ L⁻¹ should be avoided to minimise physiological perturbations.
Winter temperatures may reduce energy costs for ectotherms. However, variable mid-temperate and low-latitude winters may interact with scaling of size, metabolism, and energy reserves to cause energy ...deficits and require trade-offs between foraging and predation. A dynamic optimization model explored how ration, fall fat, and both non- and size-selective predation influenced foraging (i.e., fast or forage) and energy allocation (i.e., length or fat) decisions that maximize winter survival of age-0 largemouth bass (Micropterus salmoides). During a mid-latitude (38° N) winter, a pond experiment in which age-0 fish occurred with or without adult conspecific predators tested a subset of the model. In the model without predators, winter foraging occurred, with small size only reducing survival when low ration and low fall fat caused small fish to exhaust reserves. With predation, all sizes foraged to maintain mass and fat reserves when ration was sufficiently high, with small fish also growing in length. When modeled predation was nonselective, size-dependent mortality varied in complex ways. In contrast, size-selective predators consistently reduced survival of small fish. Generally consistent with the model, fish in ponds without predators gained mass and energy content, while those with predators only maintained these parameters. All small individuals grew more than large counterparts in length. Mortality in ponds never depended on size but was ~20% higher with predators. Energy deficits often demand active foraging during mid-temperate winters, with predation rather than energy depletion influencing size-dependent survival.
PDF
