Isosbestic Points: Theory and Applications

We analyze the sharpness of crossing ("isosbestic") points of a family of curves which are observed in many quantities described by a function f(x,p), where x is a variable (e.g., the frequency) and p a parameter (e.g., the temperature). We show that if a narrow crossing region is observed near x* for a range of parameters p, then f(x,p) can be approximated by a perturbative expression in p for a wide range of x. This allows us, e.g., to extract the temperature dependence of several experimentally obtained quantities, such as the Raman response of HgBa2CuO4+delta, photoemission spectra of thin VO2 films, and the reflectivity of CaCu3Ti4O12, all of which exhibit narrow crossing regions near certain frequencies. We also explain the sharpness of isosbestic points in the optical conductivity of the Falicov-Kimball model and the spectral function of the Hubbard model.Comment: 12 pages, 11 figure

Proces schvalování učebnic v historickosrovnávací perspektivě

Cílem příspěvku je popsat postup pro udělování schvalovací doložky, který byl nedávno změněn, a porovnat jej se systémy schvalování v zahraničí. Závěrem navrhneme některé nástroje, které by mohly v českém prostředí vést ke zvyšování kvality učebnic

Avalanche analysis from multi-electrode ensemble recordings in cat, monkey and human cerebral cortex during wakefulness and sleep

Self-organized critical states are found in many natural systems, from earthquakes to forest fires, they have also been observed in neural systems, particularly, in neuronal cultures. However, the presence of critical states in the awake brain remains controversial. Here, we compared avalanche analyses performed on different in vivo preparations during wakefulness, slow-wave sleep and REM sleep, using high-density electrode arrays in cat motor cortex (96 electrodes), monkey motor cortex and premotor cortex and human temporal cortex (96 electrodes) in epileptic patients. In neuronal avalanches defined from units (up to 160 single units), the size of avalanches never clearly scaled as power-law, but rather scaled exponentially or displayed intermediate scaling. We also analyzed the dynamics of local field potentials (LFPs) and in particular LFP negative peaks (nLFPs) among the different electrodes (up to 96 sites in temporal cortex or up to 128 sites in adjacent motor and pre-motor cortices). In this case, the avalanches defined from nLFPs displayed power-law scaling in double log representations, as reported previously in monkey. However, avalanche defined as positive LFP (pLFP) peaks, which are less directly related to neuronal firing, also displayed apparent power-law scaling. Closer examination of this scaling using more reliable cumulative distribution functions (CDF) and other rigorous statistical measures, did not confirm power-law scaling. The same pattern was seen for cats, monkey and human, as well as for different brain states of wakefulness and sleep. We also tested other alternative distributions. Multiple exponential fitting yielded optimal fits of the avalanche dynamics with bi-exponential distributions. Collectively, these results show no clear evidence for power-law scaling or self-organized critical states in the awake and sleeping brain of mammals, from cat to man.Comment: In press in: Frontiers in Physiology, 2012, special issue "Critical Brain Dynamics" (Edited by He BY, Daffertshofer A, Boonstra TW); 33 pages, 13 figures. 3 table

Histone H2AX Is Phosphorylated at Sites of Retroviral DNA Integration but Is Dispensable for Postintegration Repair

The histone variant H2AX is rapidly phosphorylated (denoted {gamma}H2AX) in large chromatin domains (foci) flanking double strand DNA (dsDNA) breaks that are produced by ionizing radiation or genotoxic agents and during V(D)J recombination. H2AX-deficient cells and mice demonstrate increased sensitivity to dsDNA break damage, indicating an active role for {gamma}H2AX in DNA repair; however, {gamma}H2AX formation is not required for V(D)J recombination. The latter finding has suggested a greater dependence on {gamma}H2AX for anchoring free broken ends versus ends that are held together during programmed breakage-joining reactions. Retroviral DNA integration produces a unique intermediate in which a dsDNA break in host DNA is held together by the intervening viral DNA, and such a reaction provides a useful model to distinguish {gamma}H2AX functions. We found that integration promotes transient formation of {gamma}H2AX at retroviral integration sites as detected by both immunocytological and chromatin immunoprecipitation methods. These results provide the first direct evidence for the association of newly integrated viral DNA with a protein species that is an established marker for the onset of a DNA damage response. We also show that H2AX is not required for repair of the retroviral integration intermediate as determined by stable transduction. These observations provide independent support for an anchoring model for the function of {gamma}H2AX in chromatin repair

Recording advances for neural prosthetics

An important challenge for neural prosthetics research is to record from populations of neurons over long periods of time, ideally for the lifetime of the patient. Two new advances toward this goal are described, the use of local field potentials (LFPs) and autonomously positioned recording electrodes. LFPs are the composite extracellular potential field from several hundreds of neurons around the electrode tip. LFP recordings can be maintained for longer periods of time than single cell recordings. We find that similar information can be decoded from LFP and spike recordings, with better performance for state decodes with LFPs and, depending on the area, equivalent or slightly less than equivalent performance for signaling the direction of planned movements. Movable electrodes in microdrives can be adjusted in the tissue to optimize recordings, but their movements must be automated to be a practical benefit to patients. We have developed automation algorithms and a meso-scale autonomous electrode testbed, and demonstrated that this system can autonomously isolate and maintain the recorded signal quality of single cells in the cortex of awake, behaving monkeys. These two advances show promise for developing very long term recording for neural prosthetic applications

How to Get the Biggest Bang for Your Buck: Wildlife Monitoring on Shrublands of the Nevada Test Site

The Nevada Test Site (NTS) covers 1,375 square miles and extends over portions of both the Mojave and Great Basin Deserts. The resulting diverse and complex flora and fauna exhibit elements of both deserts. There are 20 vegetation associations, composed primarily of shrubs, nested within 10 vegetation alliances. Of the more than 1,200 invertebrates and 339 vertebrates found in these shrubland habitats, 267 are considered sensitive or protected/regulated by federal or state laws. Wildlife and wildlife habitat monitoring ensures NTS activities comply with all federal and state laws enacted for the protection of these valuable biological resources. This paper describes the monitoring approach used at this large site. Monitoring techniques include conducting preactivity surveys, repeated sampling of permanent plots, proactively monitoring sensitive species, and collaborating with other agencies and biologists. Ways to make monitoring more efficient and examples of successful monitoring and collaborations are discussed

Consistent alleviation of abiotic stress with silicon addition: a meta-analysis

1. Hundreds of single species studies have demonstrated the facility of silicon (Si) to alleviate diverse abiotic stresses in plants. Understanding of the mechanisms of Si-mediated stress alleviation is progressing, and several reviews have brought information together. A quantitative assessment of the alleviative capacity of Si, however, which could elucidate plant Si function more broadly, was lacking. 2. We combined the results of 145 experiments, predominantly on agricultural species, in a meta-analysis to statistically assess the responses of stressed plants to Si supply across multiple plant families and abiotic stresses. We interrogated our database to determine whether stressed plants increased in dry mass and net assimilation rate, oxidative stress markers were reduced, antioxidant responses were increased and whether element uptake showed consistent changes when supplied with Si. 3. We demonstrated that across plant families and stress types, Si increases dry weight, assimilation rate and chlorophyll biosynthesis and alleviates oxidative damage in stressed plants. In general, results indicated that plant family (as a proxy for accumulator type) and stress type had significant explanatory power for variation in responses. The consistent reduction in oxidative damage was not mirrored by consistent increases in antioxidant production, indicative of the several different stress alleviation mechanisms in which Si is involved. Silicon addition increased K in shoots, decreased As and Cd in roots and Na and Cd in shoots. Silicon addition did not affect Al, Ca or Mn concentration in shoots and roots of stressed plants. Plants had significantly lower concentrations of Si accumulated in shoots but not in roots when stressed. 4. Meta-analyses showed consistent alleviation by Si of oxidative damage caused by a range of abiotic stresses across diverse species. Our findings indicate that Si is likely to be a useful fertilizer for many crops facing a spectrum of abiotic stresses. Similarities in responses across families provide strong support for a role of Si in the alleviation of abiotic stress in natural systems, where it has barely been explored. We suggest this role may become more important under a changing climate and more experiments using non-agricultural species are now needed

Getting The Biggest Bang For Your Buck: Wildlife Monitoring On Shrublands Of The Nevada Test Site

The Nevada Test Site (NTS) covers 3,561 km2 and extends over portions of both the Mojave and Great Basin Deserts. The resulting diverse and complex flora and fauna exhibit elements of both deserts. There are 20 vegetation associations, composed primarily of shrubs, nested within 10 vegetation alliances. Of the more than 1,200 invertebrate and 339 vertebrate species found in these shrubland habitats, 267 are considered sensitive or protected/regulated by federal or state laws. Wildlife and wildlife habitat monitoring ensures NTS activities comply with all federal and state laws enacted for the protection of these valuable biological resources and provides ecological information that can be used to predict and evaluate the potential impacts of proposed projects and current activities on these resources. This paper describes the monitoring approach used at this large site. Monitoring strategies include conducting preactivity surveys, proactively monitoring sensitive species, monitoring long-term population trends, and collaborating with other agencies and biologists. Ways to make monitoring more efficient and examples of successful monitoring and collaborations are discussed