2,372 research outputs found
Pseudomonas aeruginosa biofilm formation and slime excretion on antibiotic-loaded bone cement
Background Infection is an infrequent but serious complication of prosthetic joint surgery. These infections will usually not clear until the implant is removed and re-implantation has a high failure rate, especially when Pseudomonas aeruginosa is involved. Material and methods We examined Pseudomonas aeruginosa biofilm formation on plain and gentamicin-loaded bone cement with confocal scanning laser microscopy (CSLM). Two different stains were applied in order to visualize and quantify the distribution of bacterial cells and extracellular polymeric substances (slime) from the bone cement surface to the top of the biofilm. Staining with LIVE/DEAD viability stain differentiated between live and dead bacteria within the biofilm, and slime production was evaluated after staining with Calcofluor white. Results CSLM showed that the biofilm was a nonuniform structure of variable thickness, with differences in local bacterial cell and slime densities. Incorporation of gentamicin in bone cement resulted in a 44% reduction in bacterial viability, while the slime density increased significantly. In addition, conventional plate counting showed the development of small-colony variants on gentamicin-loaded bone cement with a decreased sensitivity for gentamicin (MIC: 8 mg/L), as compared with normal-sized colonies taken from plain and gentamicin-loaded bone cement (MIC: 3 mg/L). The enhanced slime production on antibiotic-loaded bone cement, together with the formation of small-colony variants, resulted in decreased susceptibility to antibiotics-probably concomitant with the onset of persistent and relapsing infections. Interpretation In the clinical situation, our findings help to explain the frequent re-implantation failure of joint replacements infected with P. aeruginosa when the procedure has been performed using antibiotic-loaded bone cement
Rate Stability and Output Rates in Queueing Networks with Shared Resources
Abstract Motivated by a variety of applications in information and communication systems, we consider queueing networks in which the service rate at each of the individual nodes depends on the state of the entire system. The asymptotic behaviour of this type of networks is fundamentally different from classical queueing networks, where the service rate at each node is usually assumed to be independent of the state of the other nodes. We study the per-node rate stability and output rates for a class networks with a general capacity allocation function. More specifically, we derive necessary conditions of per-node rate stability, and give bounds for the per-node output rate and asymptotic growth rates, under mild assumptions on the allocation function. For a set of parallel nodes, we further prove the convergence of the output rates for most parameters and give a sharp characterization of the per-node rate stability. The results provide new intuition and fundamental insight in the stability and throughput behavior of queueing networks with shared resources
A call for exploratory data analysis in revenue management forecasting: A case study of a small and independent hotel in The Netherlands
Using five years of data collected from a small and independent hotel this case study explores RMS data as a means to seek new insights into occupancy forecasting. The study provides empirical evidence on the random nature of group cancellations, an important but neglected aspect in hotel revenue management modelling. The empirical study also shows that in a local market context demand differs significantly per point of time during the day, in addition to seasonal monthly and weekly demand patterns. Moreover, the study presents evidence on the nonhomogeneous Poisson nature of the probability distribution that demand follows, a crucial characteristic for forecasting modelling that is generally assumed but not reported in the hotel forecasting literature. This implies that demand is more uncertain for smaller than for larger hotels. The paper concludes by drawing attention to the critical and often overlooked role of exploratory data analysis in hotel revenue management forecasting.Coherent privaatrech
Performance model for “Just-in-Time” problems in real-time multimedia applications
Over the last few years, the use of large-scale
multimedia data applications has been growing tremendously,
and this growth is not likely to slow down in the near future.
Many multimedia applications operate in a real-time environment
(e.g., surveillance cameras, iris scans), which must meet strict
time constraints, i.e. to analyze video frames at the same rate as
a camera produces them. To meet this requirement, Grid computing
is rapidly becoming indispensable. However, the variabilities
of the software and the hardware in grid environment cause
the strong burstiness in the transmission delay of video frames.
Because the burstiness is unknown beforehand, it is difficult to
determine the right sending moments of video frames. If the
time interval between sending two sequential frames is too large,
then the service utilization may be low. If use large buffer to
guarantee the service utilization, then video frames may be outof-
date because of the long waiting time at buffer in the server
side. This problem is referred to as “Just-in-time” problem. To
solve this problem, it is essential to determine the right sending
moments of video frames, properly dealing with the trade-off
between the service utilization and the “up-to-date” of video
frames.
Motivated by this, in this paper we develop an adaptive control
method that react to the continuously changing circumstances in
grid system so as to obtain the highest service utilization on the
one hand and to keep the video frame up-to-date on the other
hand. Extensive experimental validation in our DAS-3 testbed
and the trace-driven simulation show that our method is indeed
highly effective
On Comparing the Performance of Dynamic Multi-Network Optimizations
Abstract-With a large variety of wireless access technologies available, multi-homed devices may strongly improve the performance and reliability of communication when using multiple networks simultaneously. A key question for the practical application of multi-path strategies is the granularity at which the traffic streams should be dispersed among the available networks. This level of granularity may be expected to have a major impact on both the efficiency and complexity of practical realizations. Motivated by this, we compare two dynamic strategies that operate at different levels of granularity. The first strategy, which we call network selection, requires little operational complexity and dynamically assigns an arriving application data transfer to the network that delivers the highest expected performance. Our second strategy, which we call traffic-splitting, is of higher complexity and aims to optimally split individual data transfers among the available networks. To this end, we (1) develop quantitative models that describe the performance of both strategies, (2) determine the (near-)optimal algorithms for both strategies, and (3) validate the efficiency and practical usefulness of the algorithms via extensive network simulations and experiments in a real-life testbed environment. These experimental results show that the optimal strategies obtained from the theoretical models lead to extremely well-performing solutions in practical circumstances. Moreover, the results show that the splitting of data transfers, which is easy to embed in the network requiring no information on the number of flows in the system, leads to a much better performance compared to dynamic network selection
The Ellipticities of Cluster Early-type Galaxies from z~1 to z~0: No Evolution in the Overall Distribution of Bulge-to-Disk Ratios
We have compiled a sample of early-type cluster galaxies from 0 < z < 1.3 and
measured the evolution of their ellipticity distributions. Our sample contains
487 galaxies in 17 z>0.3 clusters with high quality space-based imaging and a
comparable sample of 210 galaxies in 10 clusters at z<0.05. We select
early-type galaxies (elliptical and S0 galaxies) that fall within the cluster
R_{200}, and which lie on the red-sequence in the magnitude range -19.3 > M_B >
-21, after correcting for luminosity evolution. Our ellipticity measurements
are made in a consistent manner over our whole sample. We perform extensive
simulations to quantify the systematic and statistical errors, and find that it
is crucial to use PSF-corrected model fits. We find that neither the median
ellipticity, nor the shape of the ellipticity distribution of cluster
early-type galaxies evolves with redshift from z ~ 0 to z > 1. These results
are strongly suggestive of an unchanging overall bulge-to-disk ratio
distribution for cluster early-type galaxies over the last ~8Gyr. This result
contrasts with that from visual classifications which show that the fraction of
morphologically-selected disk-dominated early-type galaxies, or S0s, is
significantly lower at z>0.4 than at z~0. Taking the ellipticity measurements
and assuming, as in all previous studies, that the intrinsic ellipticity
distribution of both elliptical and S0 galaxies remains constant, then we
conclude from the lack of evolution in the observed early-type ellipticity
distribution that the relative fractions of ellipticals and S0s do not evolve
from z~1 to z=0 for a red-sequence selected samples of galaxies in the cores of
clusters of galaxies.Comment: 21 pages, 15 color figures, revised to match final ApJ version.
Corrected discussion of Andreon et al 1996 from previous versio
Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
We present a comprehensive mass reconstruction of the rich galaxy cluster Cl
0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing
constraints. The weak-lensing signal from a dense distribution of background
galaxies (~120 per square arcmin) across the cluster enables the derivation of
a high-resolution parameter-free mass map. The strongly-lensed objects tightly
constrain the mass structure of the cluster inner region on an absolute scale,
breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17
obtained in such a way is remarkable. It reveals a ringlike dark matter
substructure at r~75" surrounding a soft, dense core at r~50". We interpret
this peculiar sub-structure as the result of a high-speed line-of-sight
collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated
by the cluster velocity distribution. Our numerical simulation with purely
collisionless particles demonstrates that such density ripples can arise by
radially expanding, decelerating particles that originally comprised the
pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56,
but viewed the collision axis at a much later epoch. In addition, we
show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and
lensing can be resolved by treating the cluster X-ray emission as coming from a
superposition of two X-ray systems. The cluster's unusual X-ray surface
brightness profile that requires a two isothermal sphere description supports
this hypothesis.Comment: To appear in the June 1 issue of The Astrophysical Journa
Surface thermodynamic homeostasis of salivary conditioning films through polar–apolar layering
Salivary conditioning films (SCFs) form on all surfaces exposed to the oral cavity and control diverse oral surface phenomena. Oral chemotherapeutics and dietary components present perturbations to SCFs. Here we determine the surface energetics of SCFs through contact angle measurements with various liquids on SCFs following perturbations with a variety of chemotherapeutics as well as after renewed SCF formation. Sixteen-hour SCFs on polished enamel surfaces were treated with a variety of chemotherapeutics, including toothpastes and mouthrinses. After treatment with chemotherapeutics, a SCF was applied again for 3 h. Contact angles with four different liquids on untreated and treated SCF-coated enamel surfaces were measured and surface free energies were calculated. Perturbations either caused the SCF to become more polar or more apolar, but in all cases, renewed SCF formation compensated these changes. Thus, a polar SCF attracts different salivary proteins or adsorbs proteins in a different conformation to create a more apolar SCF surface after renewed SCF formation and vice versa for apolar SCFs. This polar–apolar layering in SCF formation presents a powerful mechanism in the oral cavity to maintain surface thermodynamic homeostasis—defining oral surface properties within a narrow, biological range and influencing chemotherapeutic strategies. Surface chemical changes brought about by dietary or chemotherapeutic perturbations to SCFs make it more polar or apolar, but new SCFs are rapidly formed compensating for changes in surface energetics
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