bluuebunny/crossref_metadata_2025 huggingface dataset:
Independent calculation of dose from a helical TomoTherapy unit
Authors: Gibbons John P. , Smith Koren , Cheek Dennis , Rosen Isaac
Published: February 2009

A new calculation algorithm has been developed for independently verifying doses calculated by the TomoTherapy® Hi·Art® treatment planning system (TPS). The algorithm is designed to confi rm the dose to a point in a high dose, low dose‐gradient region. Patient data used by the algorithm include the radiological depth to the point for each projection angle and the treatment sinogram file controlling the leaf opening time for each projection. The algorithm uses common dosimetric functions [tissue phantom ratio (TPR) and output factor ()] for the central axis combined with lateral and longitudinal beam profile data to quantify the off‐axis dose dependence. Machine data for the dosimetric functions were measured on the Hi·Art machine and simulated using the TPS. Point dose calculations were made for several test phantoms and for 97 patient treatment plans using the simulated machine data. Comparisons with TPS‐predicted point doses for the phantom treatment plans demonstrated agreement within 2% for both on‐axis and off‐axis planning target volumes (PTVs). Comparisons with TPS‐predicted point doses for the patient treatment plans also showed good agreement. For calculations at sites other than lung and superficial PTVs, agreement between the calculations was within 2% for 94% of the patient calculations (64 of 68). Calculations within lung and superficial PTVs overestimated the dose by an average of 3.1% () and 3.2% (), respectively. Systematic errors within lung are probably due to the weakness of the algorithm in correcting for missing tissue and/or tissue density heterogeneities. Errors encountered within superficial PTVs probably result from the algorithm overestimating the scatter dose within the patient. Our results demonstrate that for the majority of cases, the algorithm could be used without further refinement to independently verify patient treatment plans.

PACS number(s): 87.53.Bn, 87.53.Dq, 87.53.Xd
Comparison of IPSM 1990 photon dosimetry code of practice with IAEA TRS‐398 and AAPM TG‐51.
Authors: Castrillón Silvia Vargas , Henríquez Francisco Cutanda
Published: February 2009

Several codes of practice for photon dosimetry are currently used around the world, supported by different organizations. A comparison of IPSM 1990 with both IAEA TRS‐398 and AAPM TG‐51 has been performed. All three protocols are based on the calibration of ionization chambers in terms of standards of absorbed dose to water, as it is the case with other modern codes of practice. This comparison has been carried out for photon beams of nominal energies: 4 MV, 6 MV, 8 MV, 10 MV and 18 MV.

An NE 2571 graphite ionization chamber was used in this study, cross‐calibrated against an NE 2611A Secondary Standard, calibrated in the National Physical Laboratory (NPL). Absolute dose in reference conditions was obtained using each of these three protocols including: beam quality indices, beam quality conversion factors both theoretical and NPL experimental ones, correction factors for influence quantities and absolute dose measurements. Each protocol recommendations have been strictly followed. Uncertainties have been obtained according to the ISO Guide to the Expression of Uncertainty in Measurement. Absorbed dose obtained according to all three protocols agree within experimental uncertainty. The largest difference between absolute dose results for two protocols is obtained for the highest energy: 0.7% between IPSM 1990 and IAEA TRS‐398 using theoretical beam quality conversion factors.

PACS number: 87.55.tm
Effect of dental restorations and prostheses on radiotherapy dose distribution: a Monte Carlo study
Authors: Chin David W. H. , Treister Nathaniel , Friedland Bernard , Cormack Robert A. , Tishler Roy B. , Makrigiorgos G. Mike , Court Laurence E.
Published: February 2009

Dental restorations, fixed prosthodontics, and implants affect dose distribution in head and neck radiation therapy due to the high atomic number of the materials utilized. The backscatter of electrons from metallic materials due to the impinging treatment x‐ray results in localized dose enhancements. These dose enhancements cause localized mucositis in patients who have dental work, a significant clinical complication. We investigated the backscatter effect of 23 configurations of dental work using the EGS4nrc Monte Carlo (MC) simulation system. We found that all‐metal fixed partial dentures caused the highest amount of dose enhancement – up to 33% – while amalgam restorations did not cause a significant amount. Restorations with a ceramic veneer caused up to 8% enhancement. Between 3 mm and 5 mm of water‐equivalent material almost completely absorbed the backscatter. MC simulations provide an accurate estimate of backscatter dose, and may provide patient‐specific estimates in future.
Cardiac dose evaluation for 3Dimensional conformal partial breast irradiation compared with whole breast irradiation
Authors: Gale Ashley A. , Jain Anudh K. , Vallow Laura A. , Serago Christopher F. , Buskirk Steven J. , Heckman Michael G.
Published: February 2009

To compare the radiation dose to normal cardiac tissue for 3Dimensional (3D) conformal external beam partial breast irradiation (PBI) and standard whole breast irradiation (WBI), and examine the effect of tumor bed location.

For 14 patients with left breast tumors randomized on the National Surgical Adjuvant Breast and Bowel Project B‐39 protocol, computer‐generated radiotherapy treatment plans were devised for WBI and PBI. Tumor bed location was designated according to whether more than 50% of the excision cavity was medial or lateral to the nipple line. The volume of heart receiving doses of 2.5, 5, 10, and 20 Gy was calculated for all PBI and WBI plans. Dose to 5% of the heart volume (D5) and mean heart dose were also calculated. The biologically‐equivalent dose (BED) was calculated to account for the different fractionation used in PBI and WBI.

Of the 14 patients, 8 had lateral tumor beds, and 6 had medial tumor beds. The volumes of heart receiving 2.5, 5, 10, and 20 Gy were significantly lower for lateral PBI compared with WBI. For medial PBI, significant cardiac sparing was only seen at a dose of 20 Gy. The difference of D5 values was significant for lateral PBI compared with WBI , but not for medial PBI compared with WBI . The mean dose was also significantly lower for lateral PBI compared with WBI , but not for medial PBI . The results from BED calculations did not change this outcome.

Both 3D conformal PBI and standard WBI can deliver relatively low doses to the heart. For patients with lateralized tumor beds, PBI offers significant cardiac sparing compared with WBI. Patients with medial lesions have relatively similar heart dosimetry with PBI and WBI. 3D conformal PBI is an emerging treatment modality and continued participation on clinical trials is encouraged. Patients with left‐sided lesions and lateralized tumor beds warrant special consideration for PBI, given the significant cardiac dose sparing.

PACS numbers: 87.53.Tf
Dose perturbations from implanted helical gold markers in proton therapy of prostate cancer
Authors: Giebeler Annelise , Fontenot Jonas , Balter Peter , Ciangaru George , Zhu Ronald , Newhauser Wayne
Published: February 2009

Implanted gold fiducial markers are widely used in radiation therapy to improve targeting accuracy. Recent investigations have revealed that metallic fiducial markers can cause severe perturbations in dose distributions for proton therapy, suggesting smaller markers should be considered. The objective of this study was to estimate the dosimetric impact of small gold markers in patients receiving proton therapy for prostate cancer. Small, medium, and large helical wire markers with lengths of 10 mm and helix diameters of 0.35 mm, 0.75 mm, and 1.15 mm, respectively, were implanted in an anthropomorphic phantom. Radiographic visibility was confirmed using a kilovoltage x‐ray imaging system, and dose perturbations were predicted from Monte Carlo simulations and confirmed by measurements. Monte Carlo simulations indicated that size of dose perturbation depended on marker size, orientation, and distance from the beam's end of range. Specifically, the perturbation of proton dose for the lateral‐opposed‐pair treatment technique was 31% for large markers and 23% for medium markers in a typical oblique orientation. Results for perpendicular and parallel orientations were respectively lower and higher. Consequently, these markers are not well suited for use in patients receiving proton therapy for prostate cancer. Dose perturbation was not observed for the small markers, but these markers were deemed too fragile for transrectal implantation in the prostate.

PACS number: 87.53.Pb
Stereotactic radiotherapy for lung cancer using a flattening filter free Clinac
Authors: Vassiliev Oleg N. , Kry Stephen F. , Chang Joe Y. , Balter Peter A. , Titt Uwe , Mohan Radhe
Published: February 2009

The objective of this study was to assess the feasibility of stereotactic radiotherapy for early stage lung cancer using photon beams from a Varian Clinac accelerator operated without a flattening filter. Treatment plans were generated for 10 lung cancer patients with isolated lesions less than 3 cm in diameter. For each patient, two plans were generated, one with and one without the flattening filter. Plans were generated with Eclipse 8.0 (Varian Medical Systems) commissioned with beam data measured on a Clinac 21EX (Varian Medical Systems) operated with and without the flattening filter. Removal of the flattening filter increased the dose rate. The median beam‐on time per field was reduced from 25 sec (with the filter) to 11 sec (without the filter), increasing the feasibility of breath‐hold treatments and the efficiency of gated treatments. Differences in a dose heterogeneity index for the planning target volume between plans with flattened and unflattened beams were statistically insignificant. Differences in mean doses to organs at risk were small, typically about 10 cGy over the entire treatment. The study concludes that radiotherapy with unflattened beams is feasible and requires substantially less beam‐on time, facilitating breath‐hold and gating techniques.

PACS numbers: 87.56.bd, 87.53.Ly
Application of a Monte Carlo‐based method for total scatter factors of small beams to new solid state micro‐detectors
Authors: Francescon Paolo , Cora Stefania , Cavedon Carlo , Scalchi Paolo
Published: February 2009

The scope of this work was to apply a method for estimation of total scatter factors of the smallest beams of the Cyberknife radiosurgery system to newly available solid‐state detectors: the PTW 60008 diode, the SunNuclear EdgeDetector™ diode, and the Thomson and Nielsen TN502RDM micromosfet. The method is based on a consistency check between Monte Carlo simulation of the detectors and experimental results, and was described in a recent publication. Corrected total scatter factors were in excellent agreement with the findings of the former study. The results showed that the diodes tend to overestimate the total scatter factor of small beams, probably due to excessive scatter from the material surrounding the active layer. The correction factor for diodes and for the micromosfet, however, was found to be independent of the electron beam width. This is a desirable characteristic because it allows standard correction factors to be used for treatment units of the same type, without the need of case‐by‐case Monte Carlo simulation.

PACS numbers: 87.55.kh; 87.55.ne; 87.56.Fc.
Is farm-related job title an adequate surrogate for pesticide exposure in occupational cancer epidemiology?
Authors: MacFarlane E , Glass D , Fritschi L
Published: February 2009

Objectives:

Accurate assessment of exposure is a key factor in occupational epidemiology but can be problematic, particularly where exposures of interest may be many decades removed from relevant health outcomes. Studies have traditionally relied on crude surrogates of exposure based on job title only, for instance farm-related job title as a surrogate for pesticide exposure.

Methods:

This analysis was based on data collected in Western Australia in 2000–2001. Using a multivariate regression model, we compared expert-assessed likelihood of pesticide exposure based on detailed, individual-specific questionnaire and job specific module interview information with reported farm-related job titles as a surrogate for pesticide exposure.

Results:

Most (68.8%) jobs with likely pesticide exposure were farm jobs, but 78.3% of farm jobs were assessed as having no likelihood of pesticide exposure. Likely pesticide exposure was more frequent among jobs on crop farms than on livestock farms. Likely pesticide exposure was also more frequent among jobs commenced in more recent decades and jobs of longer duration. Our results suggest that very little misclassification would have resulted from the inverse assumption that all non-farming jobs are not pesticide exposed since only a very small fraction of non-agricultural jobs were likely to have had pesticide exposure.

Conclusions:

Classification of all farm jobs as pesticide exposed is likely to substantially over-estimate the number of individuals exposed. Our results also suggest that researchers should pay special attention to farm type, length of service and historical period of employment when assessing the likelihood of pesticide exposure in farming jobs.
Effects of Waste Oil on the Survival and Reproduction of the American Flagfish, Jordanella floridae
Authors: Hedtke Steven F. , Puglisi Frank A.
Published: February 2009

Short-term lethality tests, tests on the 30-d survival of 1-d-old larvae, and a life cycle test showed that used crankcase oil adversely affected the survival and reproduction of the American flagfish, Jordanella floridae. Four-day LC50's for juveniles in static and flow-through tests were 36 200 μL/L and 9500 μL/L, respectively, for the water-soluble fraction (wsf) of a 10% oil–water mixture and 485 μL/L and 82.7 μL/L, respectively, for oil–water emulsions. The general descriptive characteristics of the test oil and the hydrocarbon composition and concentration of 13 metals were determined for the oil and its water-soluble fraction. The life cycle test began with embryos and continued through 45 d of spawning. Egg production was impaired by exposure to 3380 μL wsf/L. Tissue residue analyses indicated the uptake of lead, cadmium, and zinc at higher exposure levels. The 30-d LC50 for larvae exposed as embryos was > 8100 μL wsf/L and for larvae unexposed as embryos was 755 μL wsf/L. The maximum acceptable toxicant concentration for the water-soluble fraction of used crankcase oil was estimated to fall between 325 and 930 μL/L. Based on the compounds identified in the water-soluble fraction, previous toxicity data, and tissue residue analyses, we speculate that zinc, lead, and cadmium probably contribute significantly to the toxicity of the waste oil tested.Key words: waste oil, used crankcase oil, American flagfish, lethality, reproduction, embryo–larvae, zinc, lead, cadmium
Stress Responses to Transportation and Fitness for Marine Survival in Coho Salmon (Oncorhynchus kisutch) Smolts
Authors: Specker J. L. , Schreck C. B.
Published: February 2009

Smolting coho salmon (Oncorhynchus kisutch) were transported experimentally at low and high densities (12 and 120 g/L) for short and long periods (4 and 12 h). Because smolts can be transplanted directly to seawater, half of the fish in each treatment were transported to tanks containing seawater and half to tanks containing freshwater. Plasma corticosteroids and glucose were elevated at unloading in all groups, and corticosteroids were still above the resting level 24 h later. Potential smoltification indicators such as plasma thyroxin concentration and gill (Na+/K+)–ATPase activity were not affected by transportation. Increased corticosteroids were correlated to increased mortality in transported salmon compared to acclimated control fish when subjected to a bioassay of stress — severe confinement. The various transport regimens did not cause increased expression of latent bacterial kidney disease. In a further experiment, smolting coho salmon were released into a stream after transport for different durations. The number of fish migrating on the 1st d appeared to be inversely related to the degree of "stress" en route, but the movements of all groups were similar thereafter. We concluded that transportation caused stress in the fish regardless of hauling regimen; that increased corticosteroids may have potential as indicators of reduced performance capacity; that the greatest stress occurred during loading and the first few hours en route; and that transported smolting coho salmon seem to be equally fit for entry into freshwater or seawater.Key words: coho salmon, stress, transportation, seawater entry, corticosteroids
Inhibition of Atlantic Salmon (Salmo salar) Hatching at Low pH
Authors: Peterson R. H. , Daye P. G. , Metcalfe J. L.
Published: February 2009

Hatching of Atlantic salmon (Salmo salar) eggs was delayed or prevented if they were exposed to water of lowered pH (4.0–5.5) after eye pigmentation had developed. Hatching subsequently could be induced by returning eggs to normal pH levels (6.6–6.8). Perivitelline pH fell rapidly to near ambient levels when eggs were exposed to low pH. It is suggested that the observed effects on hatching were due to inhibition of the hatching enzyme, chorionase.Key words: Atlantic salmon, eggs, pH, perivitelline fluid, chorionase
Viral Erythrocytic Necrosis: Some Physiological Consequences of Infection in Chum Salmon (Oncorhynchus keta)
Authors: MacMillan John R. , Mulcahy Dan , Landolt Marsha
Published: February 2009

Erythroid cells in chum salmon (Oncorhynchus keta) susceptible to infection with erythrocytic necrosis virus (ENV) were examined by light and electron microscopy. Cells of stages II, III, IV, V, and VI contained complete eyrthrocytic necrosis virions in the cytoplasm. Viruses closely resembling ENV were also detected in the nuclei of some erythroblasts. Some secondary consequences of ENV infection were a threefold greater mortality rate from vibriosis, a significantly decreased tolerance to oxygen depletion, and a decreased ability to regulate serum sodium and potassium in saltwater.Key words: viral erythrocytic necrosis, erythroblasts, pathogenesis
Plasma Cortisol Levels of Fingerling Rainbow Trout (Salmo gairdneri) at Rest, and Subjected to Handling, Confinement, Transport, and Stocking
Authors: Barton Bruce A. , Peter Richard E. , Paulencu Christine R.
Published: February 2009

Fingerling rainbow trout, acclimated to hatchery raceways or laboratory aquaria, had low plasma cortisol levels (≤ 2 ng/mL), with no apparent daily cycle in levels. Netting of cohorts out of an aquarium, without agitation, did not cause a rise in plasma cortisol concentrations in remaining fish. However, following 90 s of handling and confinement by netting, fingerlings had a sharp rise in plasma cortisol to a peak at 15 min, and then a gradual decline to the basal level over 2 h. Gentle agitation and intermittent restraint with a dip net in the aquarium caused a gradual increase in plasma cortisol concentrations. Intense handling and severe confinement caused a rapid increase in plasma cortisol to a plateau, two to four times greater than the peak levels found in fingerlings subjected to the less vigorous stressors; high levels of plasma cortisol were maintained to the median tolerance limit. During a stocking operation, there was a rapid rise in plasma cortisol concentrations during the initial capture from the rearing ponds, and high levels were maintained through to stocking into the lake 6 h and 10 min later, although a small decrease occurred during transit while the fish were in the truck tanks. After stocking, plasma cortisol concentrations in caged fingerlings did not decrease to the basal level until 8 d poststocking.Key words: rainbow trout, fingerlings, plasma cortisol, cycles, handling stress, stocking stress
Study of Haematractidium scombri in Atlantic Mackerel, Scomber scombrus
Authors: MacLean Sharon A.
Published: February 2009

The prevalence of Haematractidium scombri, an intraerythrocytic protozoan, was studied over a 3-yr period in Atlantic mackerel migrating off Chincoteague, Virginia. In 1974, 24%, in 1975, 42%, and in 1976, 45.3% of the fish examined were infected. Age-2 mackerel (measuring 25–28 cm fork length) were more frequently and more heavily infected than older fish. Adult mackerel from Boothbay Harbor, Maine, and from the bottom overwintering population in the Gulf of Maine also were infected; however, H. scombri was not found in blood smears of age-0 mackerel from Montauk, Long island, New York. Haematractidium was not found in tissue sections, but structures that might be exoerythrocytic stages were seen in kidney and spleen imprints.Key words: Haematractidium, protozoan, mackerel, Scomber
Spring Transition Period in Lake Ontario — A Numerical Study of the Causes of the Large Biological and Chemical Gradients
Authors: Scavia Donald , Bennett John R.
Published: February 2009

A two-dimensional model that calculates physical transport, as well as in situ biological and chemical transformations, accurately simulates observations made along a north–south transect in Lake Ontario during April–June 1972. Simulation results show that, during the transition period between spring and summer, the inshore–offshore structure of biological and chemical distributions is controlled by the interaction of in situ processes and differences in vertical mixing on either side of the 4° isotherm. Owing to reversals in flow patterns, the effect of advection is to reduce concentration gradients, but the effect on overall distributions is minimal. An analysis of sinking losses in one- and two-dimensional models indicates that the artificially low sinking rates used in one-dimensional models of the Great Lakes result from the neglect of upwelling.Key words: Lake Ontario; model, hydrodynamic, ecological; sinking, upwelling, convection cells, chemical distributions
Dynamics of Selenium in Mercury-Contaminated Experimental Freshwater Ecosystems
Authors: Rudd John W. M. , Turner Michael A. , Townsend Bruce E. , Swick Alison , Furutani Akira
Published: February 2009

The simultaneous movement of radiolabeled selenium and mercury was followed in experimental aquatic ecosystems ([Formula: see text] tube enclosures) set into a mercury-contaminated lake. The experimental treatments consisted of increasing stable selenium or sulfate water concentrations, addition of an aquatic herbicide, and isolation of a portion of the water column from contact with sediments. Selenium and mercury did not move together through the ecosystems either geochemically or biologically. Selenium bioaccumulation was rapid by fish, crayfish, and haptobenthos and was enhanced by increased sulfate concentration and in the absence of exposure to bottom sediments. It was reduced in the presence of aquatic herbicides. A selenium concentration of 0.1 mg/L did not affect the rate of movement of mercury out of the water column but it did stabilize the movement of mercury among various compartments in the water column. Elevated selenium appeared to retard the rate of mercury bioaccumulation by fish, crayfish, and haptobenthos. Preliminary observations of selenium toxicity to several aquatic organisms were carried out. The possibility of using selenium as an ameliorating agent for heavy metal polluted freshwater systems is discussed.Key words: selenium, mercury, methylmercury, fish, crayfish
Necessary Components of Economic Surplus in Fisheries Economics
Authors: Anderson Lee G.
Published: February 2009

There are four main types of economic surpluses that can be achieved when exploiting a fishery. They are rent to the productive nature of the fish stock, normal factor rents to inputs, consumer surplus, and what is called here, worker satisfaction bonus, WSB. The latter refers to nonmonetary benefits individuals can obtain from participating in commercial fishing and, to be complete, in other occupations as well. It is discussed frequently, but has never received any formal treatment in the literature. In this paper the logic behind WSB in the fishing industry is discussed and its implications on policy is shown. A detailed model is developed which can show how all of the components of economic surplus relate to one another and how they will vary at different levels of output.Key words: fisheries economics, economic surplus, worker satisfaction bonus, maximum economic yield
Temporal and Spatial Scales in Phytoplankton Ecology. Mechanisms, Methods, Models, and Management
Authors: Harris Graham P.
Published: February 2009

This article is essentially a review of the temporal and spatial scales of variability in both marine and freshwater planktonic environments and the algal responses to those scales. I assert that there are problems with our present understanding of these scales and the use of inappropriate assumptions concerning the occurrence of steady-state conditions. In a nonsteady-state environment the concepts of limiting nutrients must be changed, and the extrapolation from culture to field conditions is fraught with problems. In this paper I review the evidence for the existence and importance of small-scale, high frequency and large-scale, low frequency variation in the planktonic environment and show that such variation fundamentally affects our understanding of existing processes. Methodology and models must also reflect the true scales of variability which exist. I show that there are, at present, problems with our understanding of planktonic processes which greatly affect our ability to manage water quality. New concepts and models are urgently needed. Finally I propose a new model of community structure and process in variable environments which accounts for the correct 'algal' scales of perturbation and response and allows certain predictions to be made. It is possible to reconcile certain problems and controversies in the literature by the use of such a model. An enhanced ability to manage planktonic systems should result from an improved understanding of the true scales of variability which exist.Key words: lakes, oceans, phytoplankton, communities, nutrients, models, management, eutrophication, fluctuations, scales
Improving the prediction of the dynamic modulus of fine-graded asphalt concrete mixtures at high temperatures
Authors: Harran Ghareib , Shalaby Ahmed
Published: February 2009

Predictive techniques for estimating the asphalt concrete dynamic modulus, |E*|, from mixture volumetric properties are widely used in pavement design and evaluation. The reliability of these techniques is lowest at high service temperatures above 35 °C. Rutting is one of the major distresses in asphalt pavements and is considered highly sensitive to |E*| at high temperatures. The objective of this paper is to improve the reliability in the prediction of |E*| at high temperatures using parameters that reflect the gradation of aggregates. A linear model is proposed to adjust the predicted |E*| for fine-graded mixtures using a new gradation parameter. The analysis was performed on 24 mixtures prepared from various aggregate gradations and types, and several binder grades. Reasonable results were predicted for the calibration data and a validation dataset from the literature. The correlation between |E*| at high temperatures and the gradation parameter improved when it was carried out independently on fine- and coarse-graded mixtures.
Hydrometeorological validation of a Canadian Regional Climate Model simulation within the Chaudière and Châteauguay watersheds (Québec, Canada)
Authors: Gagnon P. , Konan B. , Rousseau A.N. , Slivitzky M.
Published: February 2009

This study involved regional validation of a recently developed Canadian Regional Climate Model (CRCM) simulation (version 4.1.1). Four hydrometeorological variables, minimum and maximum daily temperatures, total precipitation, and total runoff, were examined within the Châteauguay and Chaudière watersheds, Québec, Canada. These watersheds, located in southern Québec, are smaller in area (2530 and 6682 km2, respectively) than the size of watersheds usually used to validate this type of model (104–106 km2). The objective of the study was to evaluate if the model could reproduce data similar to field observations within these watersheds. A successful model could be used to produce reliable predictions regarding future climate change effects on watershed hydrology within any given watershed demonstrating similar climatological variables. Results show that even though the CRCM can produce reliable results, there remains a significant bias for each variable at least during one season. Analyses show that the bias for maximum temperature is not very strong (<1 °C) within either of the studied watersheds. However, minimum temperature is clearly underestimated (≈2 °C) in winter and in spring within both watersheds. Total precipitation is significantly overestimated in winter, spring and summer within the Châteauguay watershed (11%, 35%, and 30%, respectively), but for the Chaudière watershed overestimation is less than 5%. Total runoff is strongly overestimated in both watersheds for most of the annual cycle (>30%) and is highly variable in winter and spring. Ideally, the results of this study will be used to guide future studies on the causes of CRCM bias and ultimately lead to model improvement.
Impact of the process of isolating humic acids from peat on their propertiesA paper submitted to the Journal of Environmental Engineering and Science.
Authors: Sire Janis , Klavins Maris , Kreismanis Juris , Jansone Santa
Published: February 2009

Humic substances (HS) can be isolated in preparative quantities from low rank coal, peat, and soil. Traditionally, treatment with solutions of NaOH, KOH, or metal salts (K4P2O7) has been used for their isolation. The aim of this article is to study the effectiveness of different technologies in extracting HS from peat as well as the impact of the different extractive technologies on the properties of the isolated HS. Yields of HS depend very much on the extraction process (extractant, temperature, pretreatment procedures, solvent, mixing intensity); however, the properties of the substances obtained (molecular mass, number of functional groups, spectral characteristics) differ significantly. Yields of HS can be associated with the degree of destruction of the peat fibres and intensive destruction technologies provide opportunities to obtain HS from peat in higher yields than traditional extraction methods. However, during the extraction process, significant degradation of the humic molecules takes place.
FAST EXPONENTIAL-TIME ALGORITHMS FOR THE FOREST COUNTING AND THE TUTTE POLYNOMIAL COMPUTATION IN GRAPH CLASSES
Authors: GEBAUER HEIDI , OKAMOTO YOSHIO
Published: February 2009

We prove # P -completeness for counting the number of forests in regular graphs and chordal graphs. We also present algorithms for this problem, running in O *(1.8494m) time for 3-regular graphs, and O *(1.9706m) time for unit interval graphs, where m is the number of edges in the graph and O *-notation ignores a polynomial factor. The algorithms can be generalized to the Tutte polynomial computation.
A NEAR-OPTIMAL BROADCASTING PROTOCOL FOR MOBILE VIDEO-ON-DEMAND
Authors: HUNG REGANT Y. S. , TING H. F.
Published: February 2009

The advance of wireless and mobile technology introduces a new type of Video-on-Demand (VOD) systems, namely the mobile VOD systems, that provide VOD services to mobile clients. It is a challenge to design broadcasting protocols for such systems because of the following special requirements: (1) fixed maximum bandwidth requirement: the maximum bandwidth required for broadcasting a movie should be fixed and independent of the number of requests, (2) load adaptivity: the total bandwidth usage should be dependent on the number of requests; the fewer the requests the smaller the total bandwidth usage, and (3) clients sensitivity: the system should be able to support clients with a wide range of heterogeneous capabilities. In the literature, there are some partial solutions that give protocols meeting one or two of the above requirements. In this paper, we give the first protocol that meets all of the three requirements. The performance of our protocol is optimal up to a small constant factor.
ON SPANNERS OF GEOMETRIC GRAPHS
Authors: GUDMUNDSSON JOACHIM , SMID MICHIEL
Published: February 2009

Given a connected geometric graph G, we consider the problem of constructing a t-spanner of G having the minimum number of edges. We prove that for every real number t with [Formula: see text], there exists a connected geometric graph G with n vertices, such that every t-spanner of G contains Ω(n1+1/t) edges. This bound almost matches the known upper bound, which states that every connected weighted graph with n vertices contains a t-spanner with O(n1+2/(t-1)) edges. We also prove that the problem of deciding whether a given geometric graph contains a t-spanner with at most K edges is NP-hard. Previously, this NP-hardness result was only known for non-geometric graphs.
KNOWLEDGE STATES FOR THE CACHING PROBLEM IN SHARED MEMORY MULTIPROCESSOR SYSTEMS
Authors: BEIN WOLFGANG , LARMORE LAWRENCE L. , REISCHUK RÜDIGER
Published: February 2009

Multiprocessor systems with a global shared memory provide logically uniform data access. To hide latencies when accessing global memory each processor makes use of a private cache. Several copies of a data item may exist concurrently in the system. To guarantee consistency when updating an item a processor must invalidate copies of the item in other private caches. To exclude the effect of classical paging faults, one assumes that each processor knows its own data access sequence, but does not know the sequence of future invalidations requested by other processors. Performance of a processor with this restriction can be measured against the optimal behavior of a theoretical omniscient processor, using competitive analysis. We present a [Formula: see text]-competitive randomized online algorithm for this problem for cache size of 2, and prove a matching lower bound on the competitiveness. The algorithm is derived with the help of a new concept we call knowledge states. Finally, we show a lower bound of [Formula: see text] on the competitiveness for larger cache sizes.
PERFORMANCE ANALYSIS BASED ON THE NUMBER OF DEBUGGINGS FOR SOFTWARE SYSTEM WITH PROCESSING TIME LIMIT USING RELIABILITY GROWTH MODEL
Authors: TOKUNO KOICHI , YAMADA SHIGERU
Published: February 2009

We propose the performance evaluation method for the multi-task system with software reliability growth process. The software fault-detection phenomenon in the dynamic environment is described by the Markovian software reliability model with imperfect debugging. We assume that the cumulative number of tasks arriving at the system follows the homogeneous Poisson process. Then we can formulate the distribution of the number of tasks whose processes can be complete within a prespecified processing time limit with the infinite-server queueing model. From the model, several quantities for software performance measurement considering the real-time property can be derived and given as the functions of time and the number of debuggings. Finally, we present several numerical examples of the quantities to analyze the relationship between the software reliability characteristics and the system performance measurement.
THE PERIODIC MAINTENANCE POLICY FOR A WEIBULL LIFE-TIME SYSTEM WITH DEGRADATION RATE REDUCTION UNDER RELIABILITY LIMIT
Authors: CHENG CHUN-YUAN , CHEN MINGCHIH
Published: February 2009

From the literature, it is known that preventive maintenance (PM) can reduce the deterioration of system or equipment to a younger level. Researchers usually develop optimal PM policies based on the assumption that the PM can reduce system's age or failure rate. However, the PM actions, such as cleaning, adjustment, alignment, and lubrication work, may not always reduce system's age or failure rate. Instead, it may only reduce the degradation rate of the system to a certain level. In addition, most of the existing optimal PM policies are developed by minimizing the expected cost rate only. Yet, as demonstrated in this paper, the system will have very low reliability at the time of preventive replacement if the reliability limit is not considered.

Hence, this paper is to develop an optimal periodic PM model by minimizing the expected cost rate per unit time with the consideration of reliability limit for repairable systems with degradation rate reduction after each PM. The improvement factor method is used to measure the reduction effect of the degradation rate. The algorithm for searching the optimal solutions for this PM model is developed. Examples are also presented with discussions of parameter sensitivity and special cases.
AN ANALYSIS OF ACCELERATED PERFORMANCE DEGRADATION TESTS ASSUMING THE ARRHENIUS STRESS-RELATIONSHIP
Authors: KANG TAE HYOUNG , CHUNG SANG WOOK , YUN WON YOUNG
Published: February 2009

An analytical model is developed for accelerated performance degradation tests. The performance degradations of products at a specified exposure time are assumed to follow a normal distribution. It is assumed that the relationship between the location parameter of normal distribution and the exposure time is a linear function of the exposure time that the slope coefficient of the linear relationship has an Arrhenius dependence on temperature, and that the scale parameter of the normal distribution is constant and independent of temperature or exposure time. The method of maximum likelihood estimation is used to estimate the parameters involved. The likelihood function for the accelerated performance degradation data is derived. The approximated variance-covariance matrix is also derived for calculating approximated confidence intervals of maximum likelihood estimates. Finally we use two real examples for estimating the failure-time distribution, technically defined as the time when performance degrades below a specified level.
EVACUATION PROCESS IN TWO-DIMENSIONAL TRAFFIC FLOW MODELS
Authors: MOUSSA NAJEM
Published: February 2009

Within the framework of Biham–Middleton–Levine traffic model with origin–destination trips, we study the evacuation processes of cars in cities. Cars move from the origin to the destination points. A driver which reaches its destination disappears with rate β. It is found that the evacuation processes are greatly influenced by the origin–destination distance probability distribution. We also find that the evacuation time of drivers diverges in the form of a power law τ ∝ β-ν, with ν = 1.
MONTE CARLO APPROACH ON DOUBLE-LAYER MAGNETIC SPIN LATTICE IN ANISOTROPIC HEISENBERG MODEL
Authors: BÎRSAN EUGEN , NIGA OLIVIAN
Published: February 2009

In this paper, we investigate the magnetic properties of double-layer thin film using Monte Carlo technique, in anisotropic Heisenberg model. The magnetization, out-of-plane and in-plane magnetic susceptibilities, and also the specific heat behaviors according to temperature are investigated in order to find out the contingent magnetic ordering phases and the critical temperatures values, for two easy-axis anisotropy parameters settings. We also calculate the relative variation rate of the critical temperature along with the easy-plane anisotropy interaction parameter distribution, and we comparatively appraise the numerical obtained results, in order to get quantitative response on the physical model parameters changes. Finally, we present a finite size effect study on magnetic susceptibility, respecting the two settings physical parameters we assumed in the paper.
QUANTUM TRANSPORT THROUGH HETEROCYCLIC MOLECULES
Authors: MAITI SANTANU K. , KARMAKAR S. N.
Published: February 2009

We explore electron transport properties in molecular wires made of heterocyclic molecules (pyrrole, furan and thiophene) by using the Green's function technique. Parametric calculations are given based on the tight-binding model to describe the electron transport in these wires. It is observed that the transport properties are significantly influenced by (a) the heteroatoms in the heterocyclic molecules and (b) the molecule-to-electrodes coupling strength. Conductance (g) shows sharp resonance peaks associated with the molecular energy levels in the limit of weak molecular coupling, while they get broadened in the strong molecular coupling limit. These resonances get shifted with the change of the heteroatoms in these heterocyclic molecules. All the essential features of the electron transfer through these molecular wires become much more clearly visible from the study of our current-voltage (I-V) characteristics, and they provide several key information in the study of molecular transport.
DIELECTRIC PROPERTIES OF LEAD MAGNESIUM NIOBATE-LEAD TITANATE CERAMICS PREPARED BY MIXED-OXIDE METHOD
Authors: YIMNIRUN RATTIKORN
Published: February 2009

In this study, the (1-x) Pb ( Mg 1/3 Nb 2/3) O 3-x PbTiO 3 (when x=0.1, 0.3 and 0.5) ceramics were prepared from PMN and PT powders by a mixed-oxide method. The dielectric properties of the ceramics were measured as functions of both temperature (-150–400°C) and frequency (100 Hz–1 MHz). The results indicated that the dielectric properties of pseudo-cubic phase 0.9PMN-0.1PT and tetragonal phase 0.5PMN-0.5PT ceramics followed that of relaxor and normal ferroelectric behaviors, respectively, while the dielectric behaviors of a near MPB phase 0.7PMN-0.3PT ceramic showed a mixture of normal and relaxor ferroelectric behaviors. In addition, the Curie temperature (TC) increased with increasing PT contents, while the diffusivity decreased. This confirmed a gradual transition from a relaxor ferroelectric behavior in 0.9PMN-0.1PT to a normal ferroelectric behavior in 0.5PMN-0.5PT. The difference in dielectric behaviors was attributed to the structural symmetry of the ceramics.
UPPER BOUND OF THE TIME DERIVATIVE OF ENTROPY FOR A DYNAMICAL SYSTEM DRIVEN BY TWO KINDS OF COLORED NOISE
Authors: WANG CAN-JUN , MEI DONG-CHENG
Published: February 2009

The upper bound UB(t) of the time derivative of entropy for a dynamical system driven by both additive colored noise and multiplicative colored noise with colored cross-correlation is investigated. Based on the Fokker–Planck equation, the effects of the parameters on UB(t) are analyzed. The results show that: (i) α (the multiplicative noise intensity), D (the additive noise intensity) and τ2 (the correlation time of the additive noise) always enhance UB (t) monotonically; (ii) λ (the intensity of the cross-correlation between the multiplicative noise and the additive noise), τ1 (the correlation time of the multiplicative noise), τ3 (the correlation time of the cross-correlation) and γ (the dissipative constant) all possess a minimum, i.e., UB (t) decreases for small values and increases for large values.
STRUCTURAL, MORPHOLOGICAL CHARACTERIZATION OF Fe2-xAlxCoO4 NANOPARTICLES SYNTHESIZED BY SOL-GEL METHOD
Authors: RAGHAVENDER A. T. , JADHAV K. M.
Published: February 2009

A series of Fe 2-x Al x CoO 4 ferrite nanoparticles have been synthesized by sol-gel method. Powder X-ray diffraction (XRD), thermo gravimetric (TG) and differential thermal analysis (DTA), transmission electron microscopy (TEM) and IR spectroscopy analysis were employed to study structural and morphological characterization of these ferrite nanoparticles. The effect of substitution of Fe 3+ by Al 3+ ions on the structural properties of cobalt ferrite nanoparticles was investigated. The crystallite (D) is found in the range 39 nm to 6 nm, which decreases with increasing aluminum content. The values of lattice parameters (a), X-ray density (dx), hopping length (L A , L B ) decreases with aluminum content. The tetrahedral bond (d AX ), octahedral bond (d BX ), tetra edge (d AXE ) and octa edge (d BXE ) (shared and unshared) showed the linear decrease with the increasing aluminum content x. IR spectroscopy analysis revealed the chemical and structural changes taking place in the combustion reaction.
ENHANCEMENT OF STOCHASTIC RESONANCE IN SPATIALLY EXTENDED SYSTEMS BY MEANS OF DELAYED COUPLING
Authors: JEŻO M. , KRAWIECKI A.
Published: February 2009

Stochastic resonance in a chain of coupled threshold elements driven by a spatiotemporal periodic signal and noise is studied. It is shown that stochastic resonance can be enhanced for a fixed coupling strength by introducing proper time delays in the coupling terms which balance the effect of the phase difference between the periodic signals at the input of the interacting elements. Hence, in spatially extended systems driven by spatiotemporal periodic signals, stochastic resonance can be controlled by a delayed coupling. This method of controlling stochastic resonance is robust against random perturbations of the periodicity of the input signal and of the individual time delays.
ON SYNCHRONIZATION OF DISCRETE-TIME MARKOVIAN JUMPING STOCHASTIC COMPLEX NETWORKS WITH MODE-DEPENDENT MIXED TIME-DELAYS
Authors: LIU YURONG , WANG ZIDONG , LIU XIAOHUI
Published: February 2009

In this paper, the synchronization problem is investigated for a new class of discrete-time complex networks. Such complex networks involve the Markovian jumping parameters, mode-dependent discrete and distributed time-delays, constant and delayed couplings, as well as multiple stochastic disturbances. The stochastic disturbances influence the constant coupling term, the delayed coupling term, as well as the overall network dynamics, which could better describe the dynamical behavior of a coupled complex network presented within a noisy environment. With help from the Lyapunov functional method and the properties of Kronecker product, we employ the stochastic analysis techniques to derive several delay-dependent sufficient conditions under which the coupled complex network is asymptotically synchronized in the mean square. The criteria obtained in this paper are in the form of LMIs whose solution can be easily calculated using the standard numerical software. It is shown that our main results can cover many existing ones reported in the literature. A numerical example is presented to illustrate the usefulness of our results.
FALSIFICATION OF THE ATMOSPHERICCO2GREENHOUSE EFFECTS WITHIN THE FRAME OF PHYSICS
Authors: GERLICH GERHARD , TSCHEUSCHNER RALF D.
Published: February 2009

The atmospheric greenhouse effect, an idea that many authors trace back to the traditional works of Fourier (1824), Tyndall (1861), and Arrhenius (1896), and which is still supported in global climatology, essentially describes a fictitious mechanism, in which a planetary atmosphere acts as a heat pump driven by an environment that is radiatively interacting with but radiatively equilibrated to the atmospheric system. According to the second law of thermodynamics, such a planetary machine can never exist. Nevertheless, in almost all texts of global climatology and in a widespread secondary literature, it is taken for granted that such a mechanism is real and stands on a firm scientific foundation. In this paper, the popular conjecture is analyzed and the underlying physical principles are clarified. By showing that (a) there are no common physical laws between the warming phenomenon in glass houses and the fictitious atmospheric greenhouse effects, (b) there are no calculations to determine an average surface temperature of a planet, (c) the frequently mentioned difference of 33° is a meaningless number calculated wrongly, (d) the formulas of cavity radiation are used inappropriately, (e) the assumption of a radiative balance is unphysical, (f) thermal conductivity and friction must not be set to zero, the atmospheric greenhouse conjecture is falsified.