607 research outputs found
Homotopy hyperbolic 3-manifolds are hyperbolic
This paper introduces a rigorous computer-assisted procedure for analyzing hyperbolic 3-manifolds. This procedure is used to complete the proof of several long-standing rigidity conjectures in 3-manifold theory as well as to provide a new lower bound for the volume of a closed orientable hyperbolic 3-manifold
The gray matter structural connectome and its relationship to alcohol relapse: Reconnecting for recovery.
Gray matter (GM) atrophy associated with alcohol use disorders (AUD) affects predominantly the frontal lobes. Less is known how frontal lobe GM loss affects GM loss in other regions and how it influences drinking behavior or relapse after treatment. The profile similarity index (PSI) combined with graph analysis allows to assess how GM loss in one region affects GM loss in regions connected to it, ie, GM connectivity. The PSI was used to describe the pattern of GM connectivity in 21 light drinkers (LDs) and in 54 individuals with AUD (ALC) early in abstinence. Effects of abstinence and relapse were determined in a subgroup of 36 participants after 3 months. Compared with LD, GM losses within the extended brain reward system (eBRS) at 1-month abstinence were similar between abstainers (ABST) and relapsers (REL), but REL had also GM losses outside the eBRS. Lower GM connectivities in ventro-striatal/hypothalamic and dorsolateral prefrontal regions and thalami were present in both ABST and REL. Between-networks connectivity loss of the eBRS in ABST was confined to prefrontal regions. About 3 months later, the GM volume and connectivity losses had resolved in ABST, and insula connectivity was increased compared with LD. GM losses and GM connectivity losses in REL were unchanged. Overall, prolonged abstinence was associated with a normalization of within-eBRS connectivity and a reconnection of eBRS structures with other networks. The re-formation of structural connectivities within and across networks appears critical for cognitive-behavioral functioning related to the capacity to maintain abstinence after outpatient treatment
Theoretical models for predicting the effect of bridging group recognition and conjugate substitution on hapten enzyme immunoassay dose-response curves
Models for predicting the effect of immunological recognition of the bridge group on the dose-response curves obtained with heterogeneous hapten enzyme immunoassays are presented. Appropriate theoretical treatment shows that the greater affinity of antibodies toward the enzyme-labeled species than for the unlabeled hapten analyte results in assays with limited detection capabilities. This problem is compounded when enzyme conjugates possessing multiple haptens are used. In equilibrium type competitive arrangements, the concentrations of binder and labeled hapten may be optimized to some extent to improve assay performance. However, the results presented show that only when assays are performed in a sequential binding mode using carefully controlled timing of reagent incubations can the detection capabilities of the assays be fully maximized for analyte measurements. Unfortunately, it is also shown that such sequential binding approaches render the assays essentially nonselective. The effect of decreasing the affinity of the binder to the enzyme-labeled hapten relative to the unlabeled analyte by using heterologous conjugates in equilibrium arrangements is shown to improve detection capabilities but also at the expense of reduced selectivity. Suggestions for reagent concentrations and conjugate substitution (degree of conjugation), which provide optimized dose-response curves at a given ED50 value, are also presented as are proposals for using different binders which do not exhibit bridging group recognition.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26116/1/0000192.pd
Homogeneous enzyme-linked competitive binding assay for biotin based on the avidin-biotin interaction
A homogeneous enzyme-linked competitive-binding assay for biotin with glucose-6-phosphate dehydrogenase (G6PDH), is described. This assay is based on the interaction between a G6PDH/biotin conjugate with avidin, a natural binder for biotin. In the absence of biotin in the assay mixture, this interaction results in 100% inhibition of the enzyme conjugate. In the presence of biotin, the enzymatic activity of the conjugate is regained in an amount related to the concentration of the vitamin in the sample. Extremely steep, gate-like dose/response curves, attributable to the relative binding affinities of avidin for biotin and the conjugate, are observed. The detection limits of the system vary with the amounts of avidin and enzyme/biotin conjugate used. The method is rapid and sensitive and is evaluated for the direct determination of biotin in vitamin tablets.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27454/1/0000494.pd
How Acute and Chronic Alcohol Consumption Affects Brain Networks: Insights from Multimodal Neuroimaging
Background—
Multimodal imaging combining 2 or more techniques is becoming increasingly
important because no single imaging approach has the capacity to elucidate all clinically relevant
characteristics of a network.
Methods—
This review highlights recent advances in multimodal neuroimaging (i.e., combined
use and interpretation of data collected through magnetic resonance imaging [MRI], functional
MRI, diffusion tensor imaging, positron emission tomography, magnetoencephalography, MR
perfusion, and MR spectroscopy methods) that leads to a more comprehensive understanding of
how acute and chronic alcohol consumption affect neural networks underlying cognition, emotion,
reward processing, and drinking behavior.
Results—
Several innovative investigators have started utilizing multiple imaging approaches
within the same individual to better understand how alcohol influences brain systems, both during
intoxication and after years of chronic heavy use.
Conclusions—
Their findings can help identify mechanism-based therapeutic and
pharmacological treatment options, and they may increase the efficacy and cost effectiveness of
such treatments by predicting those at greatest risk for relapse
Baryon form factors: Model-independent results
Baryon form factors can be analyzed in a largely model-independent fashion in
terms of two complementary approaches. These are chiral perturbation theory and
dispersion relations. I review the status of dispersive calculations of the
nucleon electromagnetic form factors in the light of new data. Then, I present
the leading one-loop chiral perturbation theory analysis of the hyperon and the
strange nucleon form factors. Open problems and challenges are also discussed.Comment: 10 pp, LaTeX, 10 figures, plenary talk, NUCLEON '99, Frascati, June
1999, to appear in the proceedings (Nucl. Phys. A), typos corrected,
references update
Further studies on the potentiometric salicylate response of polymeric membranes doped with tin(IV)-tetraphenylporphyrins
The chemistry leading to the selective potentiometric response toward salicylate of polymer membranes doped with 5,10,15,20-tetraphenyl(porphyrinato)tin(IV) dichloride (Sn(TPP)Cl2) is examined via 119Sn NMR, 3H2O uptake, spectrophotometric, and solution conductometric techniques. The response properties of ion-selective electrodes prepared with such membranes suggest a complex mechanism of anion binding within the membrane phase. In the pure organic phase, spectroscopic data indicate that salicylate binds directly to one or both axial coordination sites of Sn(IV), displacing the initial chloride ligands. In the presence of water, however, both chloride and salicylate are displaced by water molecules, resulting in a dipositively charged metalloporphyrincation. Furthermore, conductance measurements point to the formation of salicylate--porphyrin complexes with greater than 2:1 stoichiometry. The results of these studies are discussed in conjunction with the anomalous cationic emf response of Sn(TPP)Cl2-based membranes at high concentrations of salicylate. A response mechanism is proposed which involves outer-sphere coordination of salicylate to a diaquo ligated metalloporphyrin as a key step in the observed anion extraction/equilibrium with the membrane phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29841/1/0000188.pd
Decoupling Inflation From the String Scale
When Inflation is embedded in a fundamental theory, such as string theory, it
typically begins when the Universe is already substantially larger than the
fundamental scale [such as the one defined by the string length scale]. This is
naturally explained by postulating a pre-inflationary era, during which the
size of the Universe grew from the fundamental scale to the initial
inflationary scale. The problem then arises of maintaining the [presumed]
initial spatial homogeneity throughout this era, so that, when it terminates,
Inflation is able to begin in its potential-dominated state. Linde has proposed
that a spacetime with compact negatively curved spatial sections can achieve
this, by means of chaotic mixing. Such a compactification will however lead to
a Casimir energy, which can lead to effects that defeat the purpose unless the
coupling to gravity is suppressed. We estimate the value of this coupling
required by the proposal, and use it to show that the pre-inflationary
spacetime is stable, despite the violation of the Null Energy Condition
entailed by the Casimir energy.Comment: 24 pages, 5 eps figures, references added, stylistic changes, version
to appear in Classical and Quantum Gravit
Electromagnetic Form Factors of the Nucleon in an Improved Quark Model
Nucleon electromagnetic form factors are studied in the cloudy bag model
(CBM) with center-of-mass and recoil corrections. This is the first
presentation of a full set of nucleon form factors using the CBM. The center of
mass motion is eliminated via several different momentum projection techniques
and the results are compared. It is found that the shapes of these form factors
are significantly improved with respect to the experimental data if the Lorentz
contraction of the internal structure of the baryon is also appropriately taken
into account.Comment: revtex, 28 pages, 8 ps figs include
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