4,509 research outputs found
Calculation of the persistence length of a flexible polymer chain with short range self-repulsion
For a self-repelling polymer chain consisting of n segments we calculate the
persistence length L(j,n), defined as the projection of the end-to-end vector
on the direction of the j`th segment. This quantity shows some pronounced
variation along the chain. Using the renormalization group and
epsilon-expansion we establish the scaling form and calculate the scaling
function to order epsilon^2. Asymptotically the simple result L(j,n) ~
const(j(n-j)/n)^(2nu-1) emerges for dimension d=3. Also outside the excluded
volume limit L(j,n) is found to behave very similar to the swelling factor of a
chain of length j(n-j)/n. We carry through simulations which are found to be in
good accord with our analytical results. For d=2 both our and previous
simulations as well as theoretical arguments suggest the existence of
logarithmic anomalies.Comment: 28 pages, 8 figures, changed conten
Sec24-Dependent Secretion Drives Cell-Autonomous Expansion of Tracheal Tubes in Drosophila
Epithelial tubes in developing organs, such as mammalian lungs and insect tracheae, need to expand their initially narrow lumina to attain their final, functional dimensions [1]. Despite its critical role for organ function, the cellular mechanism of tube expansion remains unclear. Tracheal tube expansion in Drosophila involves apical secretion and deposition of a luminal matrix [2,3,4,5], but the mechanistic role of secretion and the nature of forces involved in the process were not previously clear. Here we address the roles of cell-intrinsic and extrinsic processes in tracheal tube expansion. We identify mutations in the sec24 gene stenosis, encoding a cargo-binding subunit of the COPII complex [6,7,8]. Via genetic-mosaic analyses, we show that stenosis-dependent secretion drives tube expansion in a cell-autonomous fashion. Strikingly, single cells autonomously adjust both tube diameter and length by implementing a sequence of events including apical membrane growth, cell flattening, and taenidial cuticle formation. Known luminal components are not required for this process. Thus, a cell-intrinsic program, rather than nonautonomous extrinsic cues, controls the dimensions of tracheal tubes. These results indicate a critical role of membrane-associated proteins in the process and imply a mechanism that coordinates autonomous behaviors of individual cells within epithelial structures
A Population of Teraelectronvolt Pulsar Wind Nebulae in the H.E.S.S. Galactic Plane Survey
The most numerous source class that emerged from the H.E.S.S. Galactic Plane
Survey are Pulsar Wind Nebulae (PWNe). The 2013 reanalysis of this survey,
undertaken after almost 10 years of observations, provides us with the most
sensitive and most complete census of gamma-ray PWNe to date. In addition to a
uniform analysis of spectral and morphological parameters, for the first time
also flux upper limits for energetic young pulsars were extracted from the
data. We present a discussion of the correlation between energetic pulsars and
TeV objects, and their respective properties. We will put the results in
context with the current theoretical understanding of PWNe and evaluate the
plausibility of previously non-established PWN candidates.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil
Assessing flood risk for a rural detention area
International audienceFlood detention areas serve the primary purpose of controlled water storage during large flood events in order to decrease the flood risk downstream along the river. These areas are often used for agricultural production. While various damage estimation methods exist for urban areas, there are only a few, most often simpler approaches for loss estimation in rural areas. The loss assessment can provide an estimate of the financial provisions required for the farmers' compensation (e.g., in the context of cost-benefit analyses of detention measures). Flood risk is a combination of potential damage and probability of flooding. Losses in agricultural areas exhibit a strong seasonal pattern, and the flooding probability also has a seasonal variation. In the present study, flood risk is assessed for a planned detention area alongside the Elbe River in Germany based on two loss and probability estimation approaches of different time frames, namely a monthly and an annual approach. The results show that the overall potential damage in the proposed detention area amounts to approximately 40 000 ? a?1, with approximately equal losses for each of the main land uses, agriculture and road infrastructure. A sensitivity analysis showed that the probability of flooding (i.e., the frequency of operation of the detention area) has the largest impact on the overall flood risk
The Computational Power of Beeps
In this paper, we study the quantity of computational resources (state
machine states and/or probabilistic transition precision) needed to solve
specific problems in a single hop network where nodes communicate using only
beeps. We begin by focusing on randomized leader election. We prove a lower
bound on the states required to solve this problem with a given error bound,
probability precision, and (when relevant) network size lower bound. We then
show the bound tight with a matching upper bound. Noting that our optimal upper
bound is slow, we describe two faster algorithms that trade some state
optimality to gain efficiency. We then turn our attention to more general
classes of problems by proving that once you have enough states to solve leader
election with a given error bound, you have (within constant factors) enough
states to simulate correctly, with this same error bound, a logspace TM with a
constant number of unary input tapes: allowing you to solve a large and
expressive set of problems. These results identify a key simplicity threshold
beyond which useful distributed computation is possible in the beeping model.Comment: Extended abstract to appear in the Proceedings of the International
Symposium on Distributed Computing (DISC 2015
Rainfall disaggregation for hydrological modeling: is there a need for spatial consistence?
In this study, the influence of disaggregated rainfall products with
different degrees of spatial consistence on rainfall–runoff modeling results
is analyzed for three mesoscale catchments in Lower Saxony, Germany. For the
disaggregation of daily rainfall time series into hourly values, a
multiplicative random cascade model is applied. The disaggregation is applied
on a station by station basis without consideration of surrounding stations;
hence subsequent steps are then required to implement spatial consistence.
Spatial consistence is represented here by three bivariate spatial rainfall
characteristics that complement each other. A resampling algorithm and a
parallelization approach are evaluated against the disaggregated time series
without any subsequent steps. With respect to rainfall, clear differences
between these three approaches can be identified regarding bivariate spatial
rainfall characteristics, areal rainfall intensities and extreme values. The
resampled time series lead to the best agreement with the observed ones.
Using these different rainfall products as input to hydrological modeling, we
hypothesize that derived runoff statistics – with emphasis on seasonal
extreme values – are subject to similar differences as well. However, an
impact on the extreme values' statistics of the hydrological simulations
forced by different rainfall approaches cannot be detected. Several
modifications of the study design using rainfall–runoff models with and
without parameter calibration or using different rain gauge densities lead to
similar results in runoff statistics. Only if the spatially highly resolved
rainfall–runoff WaSiM model is applied instead of the semi-distributed
HBV-IWW model can slight differences regarding the seasonal peak flows be
identified. Hence, the hypothesis formulated before is rejected in this case
study. These findings suggest that (i)Â simple model structures might
compensate for deficiencies in spatial representativeness through
parameterization and (ii)Â highly resolved hydrological models benefit from
improved spatial modeling of rainfall.</p
Deficits in explicit emotion regulation in bipolar disorder: A systematic review
Background: This study aimed to compile and synthesize studies investigating explicit emotion regulation in patients with bipolar disorder and individuals at risk of developing bipolar disorder. The importance of explicit emotion regulation arises from its potential role as a marker for bipolar disorders in individuals at risk and its potent role in therapy for bipolar disorder patients. Methods: To obtain an exhaustive compilation of studies dealing specifically with explicit emotion regulation in bipolar disorder, we conducted a systematic literature search in four databases. In the 15 studies we included in our review, the emotion-regulation strategies maintenance, distraction, and reappraisal (self-focused and situation-focused) were investigated partly on a purely behavioral level and partly in conjunction with neural measures. The samples used in the identified studies included individuals at increased risk of bipolar disorder, patients with current affective episodes, and patients with euthymic mood state. Results: In summary, the reviewed studies' results indicate impairments in explicit emotion regulation in individuals at risk for bipolar disorder, patients with manic and depressive episodes, and euthymic patients. These deficits manifest in subjective behavioral measures as well as in neural aberrations. Further, our review reveals a discrepancy between behavioral and neural findings regarding explicit emotion regulation in individuals at risk for bipolar disorders and euthymic patients. While these groups often do not differ significantly in behavioral measures from healthy and low-risk individuals, neural differences are mainly found in frontostriatal networks. Conclusion: We conclude that these neural aberrations are a potentially sensitive measure of the probability of occurrence and recurrence of symptoms of bipolar disorders and that strengthening this frontostriatal route is a potentially protective measure for individuals at risk and patients who have bipolar disorders
Strong field ionization to multiple electronic states in water
High harmonic spectra show that laser-induced strong field ionization of
water has a significant contribution from an inner-valence orbital. Our
experiment uses the ratio of H2O and D2O high harmonic yields to isolate the
characteristic nuclear motion of the molecular ionic states. The nuclear motion
initiated via ionization of the highest occupied molecular orbital (HOMO) is
small and is expected to lead to similar harmonic yields for the two isotopes.
In contrast, ionization of the second least bound orbital (HOMO-1) exhibits
itself via a strong bending motion which creates a significant isotope effect.
We elaborate on this interpretation by simulating strong field ionization and
high harmonic generation from the water isotopes using the time-dependent
Schr\"odinger equation. We expect that this isotope marking scheme for probing
excited ionic states in strong field processes can be generalized to other
molecules
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