106,156 research outputs found
The C291R Tau variant forms different types of protofibrils
Mutations in the MAPT gene can lead to disease-associated variants of tau. However, the pathological mechanisms behind these genetic tauopathies are poorly understood. Here, we characterized the aggregation stages and conformational changes of tau C291R, a recently described MAPT mutation with potential pathogenic functions. The C291R variant of the tau four-repeat domain (tau-K18; a functional fragment with increased aggregation propensity compared with the full-length protein), aggregated into a mix of granular oligomers, amorphous and annular pore-like aggregates, in native-state and heparin-treated reactions as observed using atomic force microscopy (AFM) and negative-stained electron microscopy. On extended incubation in the native-state, tau-K18 C291R oligomers, unlike wild type (WT) tau-K18, aggregated to form protofibrils of four different phenotypes: (1) spherical annular; (2) spherical annular encapsulating granular oligomers; (3) ring-like annular but non-spherical; and (4) linear protofibrils. The ring-like tau-K18 C291R aggregates shared key properties of annular protofibrils previously described for other amyloidogenic proteins, in addition to two unique features: irregular/non-spherical-shaped annular protofibrils, and spherical protofibrils encapsulating granular oligomers. Tau-K18 C291R monomers had a circular dichroism (CD) peak at ~210 nm compared with ~199 nm for tau-K18 WT. These data suggest mutation-enhanced β-sheet propensity. Together, we describe the characterization of tau-K18 C291R, the first genetic mutation substituting a cysteine residue. The aggregation mechanism of tau-K18 C291R appears to involve β-sheet-rich granular oligomers which rearrange to form unique protofibrillar structures
Simplest model to study reentrance in physical systems
We numerically investigate the necessary ingredients for reentrant behavior
in the phase diagram of physical systems. Studies on the possibly simplest
model that exhibits reentrance, the two-dimensional random bond Ising model,
show that reentrant behavior is generic whenever frustration is present in the
model. For both discrete and continuous disorder distributions, the phase
diagram in the disorder-temperature plane is found to be reentrant, where for
some disorder strengths a paramagnetic phase exists at both high and low
temperatures, but an ordered ferromagnetic phase exists for intermediate
temperatures.Comment: 4 pages, 5 figure
Sampling the ground-state magnetization of d-dimensional p-body Ising models
We demonstrate that a recently introduced heuristic optimization algorithm
[Phys. Rev. E 83, 046709 (2011)] that combines a local search with triadic
crossover genetic updates is capable of sampling nearly uniformly among
ground-state configurations in spin-glass-like Hamiltonians with p-spin
interactions in d space dimensions that have highly degenerate ground states.
Using this algorithm we probe the zero-temperature ferromagnet to spin-glass
transition point q_c of two example models, the disordered version of the
two-dimensional three-spin Baxter-Wu model [q_c = 0.1072(1)] and the
three-dimensional Edwards-Anderson model [q_c = 0.2253(7)], by computing the
Binder ratio of the ground-state magnetization.Comment: 8 pages, 6 figures, 3 table
A Method for Establishing Outdoor Recreation Project Priorities in Alaska
The authors thank Theodore Smith, Edward Kramer and Nat Goodhue
of the Division of Parks for information and comments supplied during this
study, and Frank Orth, Charles Marsh, Ed Kramer, C.E. Logsdon, and Frank
Wooding for reviewing the manuscript.
Thanks is also due the Department of Business Administration,
University of Alaska, Fairbanks, Dale Swanson, Head, for their cooperation
in this research project.The objectives of this study are to define outdoor recreation benefits to
the public and to develop a priority ranking method for proposed outdoor
recreation projects. A careful analysis of the benefits which people derive
from outdoor recreation provides a frame of reference for evaluating a
recreational facility. A project should supply those benefits which are most
highly demanded by the public. Fifteen benefits of recreation are defined
and discussed. They are divided into two major categories; those which
accrue to recreational participants and those which accrue to
non-participants.This research was supported by a grant from the Division of Parks,
State of Alaska
The Purpose of Remittances – Evidence from Germany
This paper examines the purpose of remittances using individual data of migrants in Germany. Particular attention is paid to migrants’ savings and transfers to family members in the home country. Our findings indicate that migrants who intend to stay in Germany only temporarily have a higher propensity to save and save larger amounts in their home country than permanent migrants. A similar picture emerges when considering migrants’ payments to family members abroad. The results of a decomposition analysis indicate that temporary and permanent migrants seem to have different preferences towards sending transfers abroad, while economic characteristics and the composition of households in home and host countries are less relevant.International migration, savings, remittances
Partial Adjustment Without Apology
Many kinds of economic behavior appear to be governed by discrete and occasional individual choices. Despite this, econometric partial adjustment models perform relatively well at the aggregate level. Analyzing the classic employment adjustment problem, we show how discrete and occasional microeconomic adjustment is well described by a new form of partial adjustment model that aggregates the actions of a large number of heterogeneous producers. We begin by describing a basic model of discrete and occasional adjustment at the micro level, where production units are essentially restricted to either operate with a fixed number of workers or shut down. We show that this simple model is observationally equivalent at the market level to the standard rational expectations partial adjustment model. We then construct a related, but more realistic, model that incorporates the idea that increases or decreases in the size of an establishment’s workforce are subject to fixed adjustment costs. In the market equilibrium of this model, employment responses to aggregate disturbances include changes both in employment selected by individual establishments and in the measure of establishments actively undertaking adjustment. Yet the model retains a partial adjustment flavor in its aggregate responses. Moreover, in contrast to existing models of discrete adjustment, our generalized partial adjustment model is sufficiently tractable to allow extension to general equilibrium.
Boolean decision problems with competing interactions on scale-free networks: Critical thermodynamics
We study the critical behavior of Boolean variables on scale-free networks
with competing interactions (Ising spin glasses). Our analytical results for
the disorder-network-decay-exponent phase diagram are verified using Monte
Carlo simulations. When the probability of positive (ferromagnetic) and
negative (antiferromagnetic) interactions is the same, the system undergoes a
finite-temperature spin-glass transition if the exponent that describes the
decay of the interaction degree in the scale-free graph is strictly larger than
3. However, when the exponent is equal to or less than 3, a spin-glass phase is
stable for all temperatures. The robustness of both the ferromagnetic and
spin-glass phases suggests that Boolean decision problems on scale-free
networks are quite stable to local perturbations. Finally, we show that for a
given decay exponent spin glasses on scale-free networks seem to obey
universality. Furthermore, when the decay exponent of the interaction degree is
larger than 4 in the spin-glass sector, the universality class is the same as
for the mean-field Sherrington-Kirkpatrick Ising spin glass.Comment: 14 pages, lots of figures and 2 table
Iso-array rewriting P systems with context-free iso-array rules
A new computing model called P system is a highly distributed and
parallel theoretical model, which is proposed in the area of membrane computing. Ceterchi et al. initially proposed array rewriting P systems by extending the notion of string rewriting P systems to arrays (2003). A theoretical model for picture generation using context-free iso-array grammar rules and puzzle iso-array grammar rules are introduced by Kalyani et al. (2004, 2006). Also iso-array rewriting P systems for iso-picture languages have been studied by Annadurai et al. (2008). In this paper we consider the context-free iso-array rules and context-free puzzle iso-array rules in iso-array rewriting P systems and examine the generative powers
of these P systems
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