11,735 research outputs found
Heterogeneous and rate-dependent streptavidin-biotin unbinding revealed by high-speed force spectroscopy and atomistic simulations
Receptor-ligand interactions are essential for biological function and their
binding strength is commonly explained in terms of static lock-and-key models
based on molecular complementarity. However, detailed information of the full
unbinding pathway is often lacking due, in part, to the static nature of atomic
structures and ensemble averaging inherent to bulk biophysics approaches. Here
we combine molecular dynamics and high-speed force spectroscopy on the
streptavidin-biotin complex to determine the binding strength and unbinding
pathways over the widest dynamic range. Experiment and simulation show
excellent agreement at overlapping velocities and provided evidence of the
unbinding mechanisms. During unbinding, biotin crosses multiple energy barriers
and visits various intermediate states far from the binding pocket while
streptavidin undergoes transient induced fits, all varying with loading rate.
This multistate process slows down the transition to the unbound state and
favors rebinding, thus explaining the long lifetime of the complex. We provide
an atomistic, dynamic picture of the unbinding process, replacing a simple
two-state picture with one that involves many routes to the lock and
rate-dependent induced-fit motions for intermediates, which might be relevant
for other receptor-ligand bonds.Comment: 21 pages, 4 figure
Investigations of Inhibition of Asphaltene Precipitation at High Pressure Using Bottomhole Samples
Quantum Criticality and Superconductivity in Quasi-Two-Dimensional Dirac Electronic Systems
We present a theory describing the superconducting (SC) interaction of Dirac
electrons in a quasi-two-dimensional system consisting of a stack of N planes.
The occurrence of a SC phase is investigated both at T=0 and T\neq 0, in the
case of a local interaction, when the theory must be renormalized and also in
the situation where a natural physical cutoff is present in the system. In both
cases, at T=0, we find a quantum phase transition connecting the normal and SC
phases at a certain critical coupling. The phase structure is shown to be
robust against quantum fluctuations. The SC gap is determined for T=0 and T\neq
0, both with and without a physical cutoff and the interplay between the gap
and the SC order parameter is discussed. Our theory qualitatively reproduces
the SC phase transition occurring in the underdoped regime of the high-Tc
cuprates. This fact points to the possible relevance of Dirac electrons in the
mechanism of high-Tc superconductivity.Comment: To be published in Nuclear Physics, Section B. 24 pages, 4 figure
RT-SLAM: A Generic and Real-Time Visual SLAM Implementation
This article presents a new open-source C++ implementation to solve the SLAM
problem, which is focused on genericity, versatility and high execution speed.
It is based on an original object oriented architecture, that allows the
combination of numerous sensors and landmark types, and the integration of
various approaches proposed in the literature. The system capacities are
illustrated by the presentation of an inertial/vision SLAM approach, for which
several improvements over existing methods have been introduced, and that copes
with very high dynamic motions. Results with a hand-held camera are presented.Comment: 10 page
An optimized tuned mass damper/harvester device
Much work has been conducted on vibration absorbers, such as tuned mass dampers (TMD), where significant energy is extracted from a structure. Traditionally, this energy is dissipated through the devices as heat. In this paper, the concept of recovering some of this energy electrically and reuse it for structural control or health monitoring is investigated. The energy-dissipating damper of a TMD is replaced with an electromagnetic device in order to transform mechanical vibration into electrical energy. That gives the possibility of controlled damping force whilst generating useful electrical energy. Both analytical and experimental results from an adaptive and a semi-active tuned mass damper/harvester are presented. The obtained results suggest that sufficient energy might be harvested for the device to tune itself to optimise vibration suppression
Reconstructing historical trends of polycyclic aromatic hydrocarbon deposition in a remote area of Spain using herbarium moss material
Herbarium mosses from 1879-1881, 1973-1975 and 2006-2007 were used to investigate the historical changes of atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) at a remote site located in Northern Spain. Natural abundance of nitrogen and carbon isotopes was also measured in order to assess the evolution of emissions from anthropogenic sources. Nitrogen concentrations, 13C, 13N and PAH levels were significantly higher in 19th century samples with respect to the present century samples. Moreover, PAH distribution varied over the centuries, following a tendency of light PAH enrichment. The carbon, nitrogen and PAH levels measured in the mosses tally with the historic evolution of anthropogenic emissions in the area, mainly influenced by changes of economic activities, domestic heating and road traffic density. Mosses provided by herbaria seem to offer the possibility to study long-term temporal evolution of atmospheric PAH deposition
Plausible fluorescent Ly-alpha emitters around the z=3.1 QSO0420-388
We report the results of a survey for fluorescent Ly-alpha emission carried
out in the field surrounding the z=3.1 quasar QSO0420-388 using the FORS2
instrument on the VLT. We first review the properties expected for fluorescent
Ly-alpha emitters, compared with those of other non-fluorescent Ly-alpha
emitters. Our observational search detected 13 Ly-alpha sources sparsely
sampling a volume of ~14000 comoving Mpc^3 around the quasar. The properties of
these in terms of i) the line equivalent width, ii) the line profile and iii)
the value of the surface brightness related to the distance from the quasar,
all suggest that several of these may be plausibly fluorescent. Moreover, their
number is in good agreement with the expectation from theoretical models. One
of the best candidates for fluorescence is sufficiently far behind QSO0420-388
that it would imply that the quasar has been active for (at least) ~60 Myrs.
Further studies on such objects will give information about proto-galactic
clouds and on the radiative history (and beaming) of the high-redshift quasars.Comment: 10 pages, 4 figures.Update to match the version published on ApJ 657,
135, 2007 March
Senior Recital: Pablo Gonzalez, trumpet
This recital is presented in partial fulfillment of requirements for the degree Bachelor of Music in Music Education. Mr. Gonzalez studies trumpet with Douglas Lindsey.https://digitalcommons.kennesaw.edu/musicprograms/1806/thumbnail.jp
Using forced alignment for sociophonetic research on a minority language
Until recently, large-scale phonetic analyses have been out of reach for under-documented languages, but with the advent of methodologies such as forced alignment, they have now become possible. This paper describes a methodology for applying forced alignment (using the Montreal Forced Aligner) to a speech corpus of Matukar Panau, a minority language spoken in Papua New Guinea. We obtained measurements for 68,785 vowel tokens, produced in both narrative and conversational data by 34 speakers. We examined the social conditioning on a subset of these vowels according to traditional sociolinguistic categories of age and gender, and also consider the impact of clan as a major axis of organization in this community. We show that there is a role for clan as a sociolinguistic factor in conditioning the variation observed
- âŠ