54,906 research outputs found
Semiflexible Chains under Tension
A functional integral formalism is used to derive the extension of a stiff
chain subject to an external force. The force versus extension curves are
calculated using a meanfield approach in which the hard constraint
is replaced by a global constraint where is the
tangent vector describing the chain and is the arc length. The theory
``quantitatively'' reproduces the experimental results for DNA that is subject
to a constant force.
We also treat the problems of a semiflexible chain in a nematic field. In the
limit of weak nematic field strength our treatment reproduces the exact results
for chain expansion parallel to the director. When the strength of nematic
field is large, a situation in which there are two equivalent minima in the
free energy, the intrinsically meanfield approach yields incorrect results for
the dependence of the persistence length on the nematic field.Comment: 14 pages, 1 figure available upon request, submitted to J. Chem. Phy
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Small and Medium sized Enterprisesā Collaborative Buyer-Supplier Relationships: Boundary Spanning Individual Perspectives
Boundary-spanning individuals (BSIs) play a critical role in supply chain management, especially in small and medium sized enterprises (SMEs) where interactions with buyers and suppliers can depend heavily on just a few individuals. This study, utilizing data from Korean manufacturing-sector SMEs, explores whether cooperative social value orientations of SMEsā BSIs influence the effects of collaborative buyer-supplier initiatives. The results suggested that the performance implication of decision-sharing initiative increases when BSIs have a high level of cooperative social value orientation. However, it also negatively moderates the relationship between risk/benefit sharing (involving financial losses or gains) and performance suggesting possible negative side-effects. However, we found that such orientation also negatively moderates the relationship between risk/benefit sharing (involving direct financial losses or gains) and relationship performance suggesting possible negative side-effects
boosting in kernel regression
In this paper, we investigate the theoretical and empirical properties of
boosting with kernel regression estimates as weak learners. We show that
each step of boosting reduces the bias of the estimate by two orders of
magnitude, while it does not deteriorate the order of the variance. We
illustrate the theoretical findings by some simulated examples. Also, we
demonstrate that boosting is superior to the use of higher-order kernels,
which is a well-known method of reducing the bias of the kernel estimate.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ160 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Impact of use of optical surface imaging on initial patient setup for stereotactic body radiotherapy treatments
Purpose
To evaluate the effectiveness of surface image guidance (SG) for preāimaging setup of stereotactic body radiotherapy (SBRT) patients, and to investigate the impact of SG reference surface selection on this process.
Methods and materials
284 SBRT fractions (SGāSBRT = 113, nonāSGāSBRT = 171) were retrospectively evaluated. Differences between initial (preāimaging) and treatment couch positions were extracted from the recordāandāverify system and compared for the two groups. Rotational setup discrepancies were also computed. The utility of orthogonal kVs in reducing CBCT shifts in the SGāSBRT/nonāSGāSBRT groups was also calculated. Additionally, the number of CBCTs acquired for setup was recorded and the average for each cohort was compared. These data served to evaluate the effectiveness of surface imaging in preāimaging patient positioning and its potential impact on the necessity of including orthogonal kVs for setup. Since reference surface selection can affect SG setup, daily surface reproducibility was estimated by comparing cameraāacquired surface references (VRT surface) at each fraction to the external surface of the planning CT (DICOM surface) and to the VRT surface from the previous fraction.
Results
The reduction in all initialātoātreatment translation/rotation differences when using SGāSBRT was statistically significant (RankāSum test, Ī± = 0.05). Orthogonal kV imaging kept CBCT shifts below reimaging thresholds in 19%/51% of fractions for SGāSBRT/nonāSGāSBRT cohorts. Differences in average number of CBCTs acquired were not statistically significant. The reference surface study found no statistically significant differences between the use of DICOM or VRT surfaces.
Conclusions
SGāSBRT improved preāimaging treatment setup compared to ināroom laser localization alone. It decreased the necessity of orthogonal kV imaging prior to CBCT but did not affect the average number of CBCTs acquired for setup. The selection of reference surface did not have a significant impact on initial patient positioning
First-Fit is Linear on Posets Excluding Two Long Incomparable Chains
A poset is (r + s)-free if it does not contain two incomparable chains of
size r and s, respectively. We prove that when r and s are at least 2, the
First-Fit algorithm partitions every (r + s)-free poset P into at most
8(r-1)(s-1)w chains, where w is the width of P. This solves an open problem of
Bosek, Krawczyk, and Szczypka (SIAM J. Discrete Math., 23(4):1992--1999, 2010).Comment: v3: fixed some typo
Employer-Sponsored Health Insurance: Down, But Not Out
Presents findings from twelve metropolitan areas about employers' efforts to control employee healthcare costs in response to the recession and national healthcare reform by firm size. Projects employer trends through 2014, including greater cost sharing
Exact solution of type quantum Calogero model through a mapping to free harmonic oscillators
We solve the eigenvalue problem of the type of Calogero model by
mapping it to a set of decoupled quantum harmonic oscillators through a
similarity transformation. In particular, we construct the eigenfunctions of
this Calogero model from those of bosonic harmonic oscillators having either
all even parity or all odd parity. It turns out that the eigenfunctions of this
model are orthogonal with respect to a nontrivial inner product, which can be
derived from the quasi-Hermiticity property of the corresponding conserved
quantities.Comment: 16 page
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