We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using ...eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from weakly interacting massive particles (WIMPs) with masses below ∼10 GeV/c(2). This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c(2) and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments.
This paper lays the groundwork for linking Hounsfield unit measurements to the International System of Units (SI), ultimately enabling traceable measurements across X-ray CT (XCT) machines. We do ...this by characterizing a material basis that may be used in XCT reconstruction giving linear combinations of concentrations of chemical elements (in the SI units of mol/m3) which may be observed at each voxel. By implication, linear combinations not in the set are not observable.
We formulated a model for our material basis with a set of measurements of elemental powders at four tube voltages, 80 kV, 100 kV, 120 kV, and 140 kV, on a medical XCT. The samples included 30 small plastic bottles of powders containing various compounds spanning the atomic numbers up to 20, and a bottle of water and one of air. Using the chemical formulas and measured masses, we formed a matrix giving the number of Hounsfield units per (mole per cubic meter) at each tube voltage for each of 13 chemical elements. We defined a corresponding matrix in units we call molar Hounsfield unit (HU) potency, the difference in HU values that an added mole per cubic meter in a given voxel would add to the measured HU value. We built a matrix of molar potencies for each chemical element and tube voltage and performed a singular value decomposition (SVD) on these to formulate our material basis. We determined that the dimension of this basis is two. We then compared measurements in this material space with theoretical measurements, combining XCOM cross section data with the tungsten anode spectral model using interpolating cubic splines (TASMICS), a one-parameter filter, and a simple detector model, creating a matrix similar to our experimental matrix for the first 20 chemical elements. Finally, we compared the model predictions to Hounsfield unit measurements on three XCT calibration phantoms taken from the literature.
We predict the experimental HU potency values derived from our scans of chemical elements with our theoretical model built from XCOM data. The singular values and singular vectors of the model and powder measurements are in substantial agreement. Application of the Bayesian Information Criterion (BIC) shows that exactly two singular values and singular vectors describe the results over four tube voltages. We give a good account of the HU values from the literature, measured for the calibration phantoms at several tube voltages for several commercial instruments, compared with our theoretical model without introducing additional parameters.
We have developed a two-dimensional material basis that specifies the degree to which individual elements in compounds effect the HU values in XCT images of samples with elements up to atomic number Z = 20. We show that two dimensions is sufficient given the contrast and noise in our experiment. The linear combination of concentrations of elements that can be observed using a medical XCT have been characterized, providing a material basis for use in dual-energy reconstruction. This approach provides groundwork for improved reconstruction and for the link of Hounsfield units to the SI.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Mice have a large visual field that is constantly stabilized by vestibular ocular reflex (VOR) driven eye rotations that counter head-rotations. While maintaining their extensive visual coverage is ...advantageous for predator detection, mice also track and capture prey using vision. However, in the freely moving animal quantifying object location in the field of view is challenging. Here, we developed a method to digitally reconstruct and quantify the visual scene of freely moving mice performing a visually based prey capture task. By isolating the visual sense and combining a mouse eye optic model with the head and eye rotations, the detailed reconstruction of the digital environment and retinal features were projected onto the corneal surface for comparison, and updated throughout the behavior. By quantifying the spatial location of objects in the visual scene and their motion throughout the behavior, we show that the prey image consistently falls within a small area of the VOR-stabilized visual field. This functional focus coincides with the region of minimal optic flow within the visual field and consequently area of minimal motion-induced image-blur, as during pursuit mice ran directly toward the prey. The functional focus lies in the upper-temporal part of the retina and coincides with the reported high density-region of Alpha-ON sustained retinal ganglion cells.
Fragile X syndrome, caused by a mutation in the
Fmr1 gene, is characterized by mental retardation. Several studies reported the absence of long-term potentiation (LTP) at neocortical synapses in
Fmr1 ...knockout (FMR1-KO) mice, but underlying cellular mechanisms are unknown. We find that in the prefrontal cortex (PFC) of FMR1-KO mice, spike-timing-dependent LTP (tLTP) is not so much absent, but rather, the threshold for tLTP induction is increased. Calcium signaling in dendrites and spines is compromised. First, dendrites and spines more often fail to show calcium transients. Second, the activity of L-type calcium channels is absent in spines. tLTP could be restored by improving reliability and amplitude of calcium signaling by increasing neuronal activity. In FMR1-KO mice that were raised in enriched environments, tLTP was restored to WT levels. Our results show that mechanisms for synaptic plasticity are in place in the FMR1-KO mouse PFC, but require stronger neuronal activity to be triggered.
We report results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory (CDMS II) featuring the full complement of 30 detectors. A blind analysis of data taken between October ...2006 and July 2007 sets an upper limit on the weakly interacting massive particle (WIMP) nucleon spin-independent cross section of 6.6x10;{-44} cm;{2} (4.6x10;{-44} cm;{2} when combined with previous CDMS II data) at the 90% confidence level for a WIMP mass of 60 GeV/c;{2}. This achieves the best sensitivity for dark matter WIMPs with masses above 44 GeV/c;{2}, and significantly restricts the parameter space for some favored supersymmetric models.
Fragile X syndrome (FXS), the most common form of hereditary mental retardation, is caused by a loss-of-function mutation of the Fmr1 gene, which encodes fragile X mental retardation protein (FMRP). ...FMRP affects dendritic protein synthesis, thereby causing synaptic abnormalities. Here, we used a quantitative proteomics approach in an FXS mouse model to reveal changes in levels of hippocampal synapse proteins. Sixteen independent pools of Fmr1 knock-out mice and wild type mice were analyzed using two sets of 8-plex iTRAQ experiments. Of 205 proteins quantified with at least three distinct peptides in both iTRAQ series, the abundance of 23 proteins differed between Fmr1 knock-out and wild type synapses with a false discovery rate (q-value) <5%. Significant differences were confirmed by quantitative immunoblotting. A group of proteins that are known to be involved in cell differentiation and neurite outgrowth was regulated; they included Basp1 and Gap43, known PKC substrates, and Cend1. Basp1 and Gap43 are predominantly expressed in growth cones and presynaptic terminals. In line with this, ultrastructural analysis in developing hippocampal FXS synapses revealed smaller active zones with corresponding postsynaptic densities and smaller pools of clustered vesicles, indicative of immature presynaptic maturation. A second group of proteins involved in synaptic vesicle release was up-regulated in the FXS mouse model. In accordance, paired-pulse and short-term facilitation were significantly affected in these hippocampal synapses. Together, the altered regulation of presynaptically expressed proteins, immature synaptic ultrastructure, and compromised short-term plasticity points to presynaptic changes underlying glutamatergic transmission in FXS at this stage of development.
J. Neurochem. (2009) 112, 900-912. While the ultimate dependence of brain function on its energy supply is evident, how basic neuronal parameters and network activity respond to energy metabolism ...deviations is unresolved. The resting membrane potential (Em) and reversal potential of GABA-induced anionic currents (EGABA) are among the most fundamental parameters controlling neuronal excitability. However, alterations of Em and EGABA under conditions of metabolic stress are not sufficiently documented, although it is well known that metabolic crisis may lead to neuronal hyper-excitability and aberrant neuronal network activities. In this work, we show that in slices, availability of energy substrates determines whether GABA signaling displays an inhibitory or excitatory mode, both in neonatal neocortex and hippocampus. We demonstrate that in the neonatal brain, Em and EGABA strongly depend on composition of the energy substrate pool. Complementing glucose with ketone bodies, pyruvate or lactate resulted in a significant hyperpolarization of both Em and EGABA, and induced a radical shift in the mode of GABAergic synaptic transmission towards network inhibition. Generation of giant depolarizing potentials, currently regarded as the hallmark of spontaneous neonatal network activity in vitro, was strongly inhibited both in neocortex and hippocampus in the energy substrate enriched solution. Based on these results we suggest the composition of the artificial cerebrospinal fluid, which bears a closer resemblance to the in vivo energy substrate pool. Our results suggest that energy deficits induce unfavorable changes in Em and EGABA, leading to neuronal hyperactivity that may initiate a cascade of pathological events.
In the early postnatal period, energy metabolism in the suckling rodent brain relies to a large extent on metabolic pathways alternate to glucose such as the utilization of ketone bodies (KBs). ...However, how KBs affect neuronal excitability is not known. Using recordings of single NMDA and GABA-activated channels in neocortical pyramidal cells we studied the effects of KBs on the resting membrane potential (Em) and reversal potential of GABA-induced anionic currents (EGABA), respectively. We show that during postnatal development (P3-P19) if neocortical brain slices are adequately supplied with KBs, Em and EGABA are both maintained at negative levels of about -83 and -80 mV, respectively. Conversely, a KB deficiency causes a significant depolarization of both Em (>5 mV) and EGABA (>15 mV). The KB-mediated shift in EGABA is largely determined by the interaction of the NKCC1 cotransporter and Cl⁻/HCO₃ transporter(s). Therefore, by inducing a hyperpolarizing shift in Em and modulating GABA signaling mode, KBs can efficiently control the excitability of neonatal cortical neurons.
In pyramidal cells, induction of long-term potentiation (LTP) and long-term depression (LTD) of excitatory synaptic transmission by coincidence of presynaptic and postsynaptic activity is considered ...relevant to learning processes in vivo. Here we show that temporally correlated spiking activity of a pyramidal cell and an inhibiting interneuron may cause LTD or LTP of unitary IPSPs. Polarity of change in synaptic efficacy depends on timing between Ca(2+) influx induced by a backpropagating train of action potentials (APs) in pyramidal cell dendrites (10 APs, 50 Hz) and subsequent activation of inhibitory synapses. LTD of IPSPs was induced by synaptic activation in the vicinity of the AP train (<300 msec relative to the beginning of the train), whereas LTP of IPSPs was initiated with more remote synaptic activation (>400 msec relative to the beginning of the AP train). Solely AP trains induced neither LTP nor LTD. Both LTP and LTD were prevented by 5 mm BAPTA loaded into pyramidal cells. LTD was prevented by 5 mm EGTA, whereas EGTA failed to affect LTP. Synaptic plasticity was not dependent on activation of GABA(B) receptors. It was also not affected by the antagonists of vesicular exocytosis, botulinum toxin D, and GDP-beta-S.
This paper describes a fan beam coded aperture x-ray scatter imaging system that acquires a tomographic image from each snapshot. This technique exploits the cylindrical symmetry of the scattering ...cross section to avoid the scanning motion typically required by projection tomography. We use a coded aperture with a harmonic dependence to determine range and a shift code to determine cross range. Here we use a forward-scatter configuration to image 2D objects and use serial exposures to acquire tomographic video of motion within a plane. Our reconstruction algorithm also estimates the angular dependence of the scattered radiance, a step toward materials imaging and identification.
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