4,251 research outputs found
Substrate-dependent bacterivory by intertidal benthic copepods
The trophic importance of bacteria to harpacticoid copepods in intertidal areas remains poorly understood, and so do the mechanisms of bacterial feeding. It is, for instance, unclear whether harpacticoids directly target bacterial cells, or merely co-ingest them with substrates to which bacterial cells may be attached. Here, we investigate bacterial uptake and substrate requirement for four mud intertidal species (Microarthridion littorale, Platychelipus littoralis, Delavalia palustris, Nannopus palustris) by means of 13C-labeled bacteria and biomarker fatty acids (FA). Bacterial uptake strongly depended on grazing on a primary food source but bacterial ingestion rates were low and no clear indication of copepods directly targeting bacteria was found. Delavalia was the only species that accumulated bacteria-derived FA and gained in polyunsaturated FA (PUFA) probably through bioconversion of bacteria-derived FA. In general, however, our results suggest that bacteria represent a relatively minor and low-quality food for intertidal harpacticoid copepods
Improving the nautical access to Zeebrugge harbor: a multidisciplinary study
A multidisciplinary study was set up to tackle the nautical problems faced by Zeebrugge Harbor by the Maritime Access Division of the Flemish Community. The problem is twofold: strong cross-currents at the harbor mouth hinder the entrance of the ships around high water, and the occurrence of thick muddy layers hinders the navigation in the harbor and causes very high dredging costs. The article focuses on the global project set up, and explains more in detail the numerical and physical modeling research
The impact of reduction of doublet well spacing on the Net Present Value and the life time of fluvial Hot Sedimentary Aquifer doublets
This paper evaluates the impact of reduction of doublet well spacing, below the current West Netherlands Basin standard of 1000 to 1500 m, on the Net Present Value (NPV) and the life time of fluvial Hot Sedimentary Aquifer (HSA) doublets. First, a sensitivity analysis is used to show the possible advantage of such reduction on the NPV. The parameter value ranges are derived from West Netherlands Basin HSA doublet examples. The results indicate that a reduction of well spacing from 1400 to 1000 m could already influence NPV by up to 15%. This effect would be larger in more marginally economic HSA doublets compared to the West Netherlands Basin base case scenario. The possibility to reduce well spacing is supported by finite element production simulations, utilizing detailed facies architecture models. Furthermore, our results underline the necessity of detailed facies architecture models to assess the potential and risks of HSA doublets. This factor significantly affects doublet life time and net energy production of the doublet
Further detections of OH masers in carbon stars with silicate features
A sample of J-type carbon stars was searched for OH maser emission. The new
detection of three OH lines towards two silicate carbon stars is reported. In
V778 Cyg, previously known as the main-lines (1665 and 1667 MHz) maser source,
the satellite 1612 MHz emission was discovered while in NSV 2814 the main OH
lines were detected. The presence of OH maser lines confirms the former
suggestion that oxygen-rich material is located in the vicinity (
cm) of silicate carbon stars.Comment: LaTeX2e, 4 pages with 2 figure
Defending Browsers against Drive-by Downloads: Mitigating Heap-Spraying Code Injection Attacks
Abstract. Drive-by download attacks are among the most common methods for spreading malware today. These attacks typically exploit memory corruption vul-nerabilities in web browsers and browser plug-ins to execute shellcode, and in consequence, gain control of a victim’s computer. Compromised machines are then used to carry out various malicious activities, such as joining botnets, send-ing spam emails, or participating in distributed denial of service attacks. To counter drive-by downloads, we propose a technique that relies on x86 instruc-tion emulation to identify JavaScript string buffers that contain shellcode. Our de-tection is integrated into the browser, and performed before control is transfered to the shellcode, thus, effectively thwarting the attack. The solution maintains fair performance by avoiding unnecessary invocations of the emulator, while ensur-ing that every buffer with potential shellcode is checked. We have implemented a prototype of our system, and evaluated it over thousands of malicious and le-gitimate web sites. Our results demonstrate that the system performs accurate detection with no false positives
Current Accuracy of Augmented Reality Neuronavigation Systems: Systematic Review and Meta-Analysis
BACKGROUND
Augmented reality neuronavigation (ARN) systems can overlay three-dimensional anatomy and pathology without the need for a two-dimensional external monitor. Accuracy is crucial for their clinical applicability. We performed a systematic review regarding the reported accuracy of ARN systems and compared them with the accuracy of conventional infrared neuronavigation (CIN).
OBJECTIVE
Explore the current navigation accuracy of ARN systems and compare them with CIN.
METHODS
Pubmed and Embase were searched for ARN and CIN systems. For ARN: type of system, method of patient-to-image registration, accuracy method and accuracy of the system was noted. For CIN: navigation accuracy, expressed as target registration error (TRE), was noted. A meta-analysis was performed comparing the TRE of ARN and CIN systems.
RESULTS
35 studies were included, 12 for ARN and 23 for CIN. ARN systems were divided into head-mounted display and heads-up display. In ARN, four methods were encountered for patient-to-image registration, of which point-pair matching was the one most frequently used. Five methods for assessing accuracy were described. 94 TRE measurements of ARN systems were compared with 9058 TRE measurements of CIN systems. Mean TRE was 2.5 mm (CI 95% 0.7 - 4.4) for ARN systems and 2.6 mm (CI 95% 2.1 - 3.1) for CIN systems.
CONCLUSIONS
In ARN, there seems to be lack of agreement regarding the best method to assess accuracy. Nevertheless, ARN systems seem able to achieve an accuracy comparable with CIN systems. Future studies should be prospective and compare TREs which should be measured in a standardized fashion
An improved constraint satisfaction adaptive neural network for job-shop scheduling
Copyright @ Springer Science + Business Media, LLC 2009This paper presents an improved constraint satisfaction adaptive neural network for job-shop scheduling problems. The neural network is constructed based on the constraint conditions of a job-shop scheduling problem. Its structure and neuron connections can change adaptively according to the real-time constraint satisfaction situations that arise during the solving process. Several heuristics are also integrated within the neural network to enhance its convergence, accelerate its convergence, and improve the quality of the solutions produced. An experimental study based on a set of benchmark job-shop scheduling problems shows that the improved constraint satisfaction adaptive neural network outperforms the original constraint satisfaction adaptive neural network in terms of computational time and the quality of schedules it produces. The neural network approach is also experimentally validated to outperform three classical heuristic algorithms that are widely used as the basis of many state-of-the-art scheduling systems. Hence, it may also be used to construct advanced job-shop scheduling systems.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/01 and in part by the National Nature Science Fundation of China under Grant 60821063 and National Basic Research Program of China under Grant 2009CB320601
Spin filling of a quantum dot derived from excited-state spectroscopy
We study the spin filling of a semiconductor quantum dot using excited-state
spectroscopy in a strong magnetic field. The field is oriented in the plane of
the two-dimensional electron gas in which the dot is electrostatically defined.
By combining the observation of Zeeman splitting with our knowledge of the
absolute number of electrons, we are able to determine the ground state spin
configuration for one to five electrons occupying the dot. For four electrons,
we find a ground state spin configuration with total spin S=1, in agreement
with Hund's first rule. The electron g-factor is observed to be independent of
magnetic field and electron number.Comment: 11 pages, 7 figures, submitted to New Journal of Physics, focus issue
on Solid State Quantum Informatio
HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT
Accurate photometric CoRoT space observations of a secondary seismological
target, HD 174884, led to the discovery that this star is an astrophysically
important double-lined eclipsing spectroscopic binary in an eccentric orbit (e
of about 0.3), unusual for its short (3.65705d) orbital period. The high
eccentricity, coupled with the orientation of the binary orbit in space,
explains the very unusual observed light curve with strongly unequal primary
and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT 'seismo'
passband. Without the high accuracy of the CoRoT photometry, the secondary
eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up
program provided 45 high dispersion spectra. The analysis of the CoRoT light
curve was performed with an adapted version of PHOEBE that supports CoRoT
passbands. The final solution was obtained by simultaneous fitting of the light
and the radial velocity curves. Individual star spectra were derived by
spectrum disentangling. The uncertainties of the fit were derived by bootstrap
resampling and the solution uniqueness was tested by heuristic scanning. The
results provide a consistent picture of the system composed of two late B
stars. The Fourier analysis of the light curve fit residuals yields two
components, with orbital frequency multiples and an amplitude of about 0.1
mmag, which are tentatively interpreted as tidally induced pulsations. An
extensive comparison with theoretical models is carried out by means of the
Levenberg-Marquardt minimization technique and the discrepancy between models
and the derived parameters is discussed. The best fitting models yield a young
system age of 125 million years which is consistent with the eccentric orbit
and synchronous component rotation at periastron.Comment: 15 pages, 12 figures. Accepted for publication by A&
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