These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Heterogeneity-corrected vs -uncorrected critical structure maximum point doses in breast balloon brachytherapy  

SciTech Connect

Recent studies have reported potentially clinically meaningful dose differences when heterogeneity correction is used in breast balloon brachytherapy. In this study, we report on the relationship between heterogeneity-corrected and -uncorrected doses for 2 commonly used plan evaluation metrics: maximum point dose to skin surface and maximum point dose to ribs. Maximum point doses to skin surface and ribs were calculated using TG-43 and Varian Acuros for 20 patients treated with breast balloon brachytherapy. The results were plotted against each other and fit with a zero-intercept line. Max skin dose (Acuros) = max skin dose (TG-43) ? 0.930 (R{sup 2} = 0.995). The average magnitude of difference from this relationship was 1.1% (max 2.8%). Max rib dose (Acuros) = max rib dose (TG-43) ? 0.955 (R{sup 2} = 0.9995). The average magnitude of difference from this relationship was 0.7% (max 1.6%). Heterogeneity-corrected maximum point doses to the skin surface and ribs were proportional to TG-43-calculated doses. The average deviation from proportionality was 1%. The proportional relationship suggests that a different metric other than maximum point dose may be needed to obtain a clinical advantage from heterogeneity correction. Alternatively, if maximum point dose continues to be used in recommended limits while incorporating heterogeneity correction, institutions without this capability may be able to accurately estimate these doses by use of a scaling factor.

Kim, Leonard, E-mail: kimlh@umdnj.edu [Department of Radiation Oncology, Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, NJ (United States); Narra, Venkat; Yue, Ning [Department of Radiation Oncology, Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, NJ (United States)

2013-07-01

2

Integrated photovoltaic maximum power point tracking converter  

Microsoft Academic Search

A low-power low-cost highly efficient maximum power point tracker (MPPT) to be integrated into a photovoltaic (PV) panel is proposed. This can result in a 25% energy enhancement compared to a standard photovoltaic panel, while performing functions like battery voltage regulation and matching of the PV array with the load. Instead of using an externally connected MPPT, it is proposed

Johan H. R. Enslin; Mario S. Wolf; D. B. Snyman; Wernher Swiegers

1997-01-01

3

Pulmonary carcinogenicity of inhaled particles and the maximum tolerated dose.  

PubMed Central

Chronic inhalation bioassays in rodents are used to assess pulmonary carcinogenicity for purposes of hazard identification and potentially for risk characterization. The influence of high experimental doses on tumor development has been recognized for some time and has led to the concept of maximum tolerated dose (MTD) for dose selection, with the highest dose being at the MTD. Exposure at the MTD should ensure that the animals are sufficiently challenged while at the same time the animal's normal longevity is not altered from effects other than carcinogenicity. A characteristic of exposure-dose-response relationships for chronically inhaled particles is that lung tumors are significantly increased only at high exposure levels, and that lung tumors are seen in rats only but not in mice or hamsters. This lung tumor response in rats is thought to be secondary to persistent alveolar inflammation, indicating that the MTD may have been exceeded. Thus, mechanisms of toxicity and carcinogenicity may be dose dependent and may not operate at lower doses that humans normally experience. Despite awareness of this problem, carcinogenicity bioassays that evaluate particulate compounds in rodents have not always been designed with the MTD concept in mind. This is due to several problems associated with determining an appropriate MTD for particle inhalation studies. One requirement for the MTD is that some toxicity should be observed. However, it is difficult to define what degree of toxic response is indicative of the MTD. For particle inhalation studies, various noncancer end points in addition to mortality and body weight gain have been considered as indicators of the MTD, i.e., pulmonary inflammation, increased epithelial cell proliferation, increased lung weight, impairment of particle clearance function, and significant histopathological findings at the end of a subchronic study. However, there is no general agreement about quantification of these end points to define the MTD. To determine whether pulmonary responses are indicative of the MTD, we suggest defining an MTD based on results of a multidose subchronic and chronic inhalation study with a known human particulate carcinogen, e.g., asbestos or crystalline silica. Quantification of effects in such a study using the noncancer end points listed above would identify a dose level without significant signs of toxicity at the end of the subchronic study. If this dose level still results in significant lung tumor incidence at the end of the chronic study. We will have a sound basis for characterizing the MTD and justifying its use in future particle inhalation studies. Also, a better understanding of cellular and molecular mechanisms of particle-induced lung tumors is needed to support the MTD concept. PMID:9400749

Oberdörster, G

1997-01-01

4

An integrated maximum power point tracker for photovoltaic panels  

Microsoft Academic Search

This paper proposes a maximum power point tracker (MPPT) for a photovoltaic panel, that is to be integrated with the panel during manufacturing. The MPPT is inexpensive, efficient and has few components that serve to increase the MPPT's mean time between failures (MTBF). The MPPT uses an inexpensive microcontroller to perform all of its functions. This includes maximum power point

Wernher Swiegers; Johan H. R. Enslin

1998-01-01

5

Maximum Power Point Tracking for Ocean Wave Energy Conversion  

Microsoft Academic Search

Many forms of renewable energy exist in the world's oceans, with ocean wave energy showing great potential. However, the ocean environment presents many challenges for cost-effective renewable energy conversion, including optimal control of a wave energy converter (WEC). This paper presents a maximum power point tracking (MPPT) algorithm for control of a point absorber WEC. The algorithm and testing hardware

Ean A. Amon; Ted K. A. Brekken; Alphonse A. Schacher

2012-01-01

6

Dynamic maximum power point tracker for photovoltaic applications  

Microsoft Academic Search

A dynamic process for reaching the maximum power point of a variable power source such as a solar cell is introduced. The process tracks maximum power nearly cycle-by-cycle during transients. Information from the natural switching ripple instead of external perturbation is used to support the maximizing process. The method is globally stable for DC-DC power converters, provided that a switching

Pallab Midya; Philip T. Krein; Robert J. Turnbull; Robert Reppa; Jonathan Kimball

1996-01-01

7

Individual Module Maximum Power Point Tracking for Thermoelectric Generator Systems  

NASA Astrophysics Data System (ADS)

In a thermoelectric generator (TEG) system the DC/DC converter is under the control of a maximum power point tracker which ensures that the TEG system outputs the maximum possible power to the load. However, if the conditions, e.g., temperature, health, etc., of the TEG modules are different, each TEG module will not produce its maximum power. If each TEG module is controlled individually, each TEG module can be operated at its maximum power point and the TEG system output power will therefore be higher. In this work a power converter based on noninverting buck-boost converters capable of handling four TEG modules is presented. It is shown that, when each module in the TEG system is operated under individual maximum power point tracking, the system output power for this specific application can be increased by up to 8.4% relative to the situation when the modules are connected in series and 16.7% relative to the situation when the modules are connected in parallel.

Vadstrup, Casper; Schaltz, Erik; Chen, Min

2013-07-01

8

Optimized digital Maximum Power Point Tracker implementation for satellites  

Microsoft Academic Search

Maximum Power Point Tracking MPPT for solar panels is critical for space applications where power saving gets the first priority with the availability of limited resources. Of the available methods for MPPT, the Perturb and Observe (P&O) method is accurate and simple to implement. In the MPPT design choosing the sampling time and duty cycle step size is important which

A. Ramamurthy; S. Bhattacharya

2008-01-01

9

Maximum Power Point Estimation for Photovoltaic Systems Using Neural Networks  

Microsoft Academic Search

Solar panels are the power sources in photovoltaic applications which provide electrical power. Solar panel characteristics depend on environmental conditions (solar radiation level, temperature and etc.). In this paper, estimation of maximum power point of silicon solar panels is presented. We applied two different neural networks (back propagation and RBF) for the purpose of estimation in different environmental conditions. These

M. Taherbaneh; K. Faez

2007-01-01

10

Maximum power point tracking for low power photovoltaic solar panels  

Microsoft Academic Search

A maximum power point tracker unit is developed for the optimum coupling of photovoltaic panels (PVP) to the batteries and load through a controlled DC-DC power converter (chopper). The system consists of three main units: (i) the photovoltaic panels that convert solar power to electricity; (ii) a chopper which couples the power of PVP to the load or batteries at

Mehmet BODUR; Mummer ERMIS

1994-01-01

11

Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques  

Microsoft Academic Search

The many different techniques for maximum power point tracking of photovoltaic (PV) arrays are discussed. The techniques are taken from the literature dating back to the earliest methods. It is shown that at least 19 distinct methods have been introduced in the literature, with many variations on implementation. This paper should serve as a convenient reference for future work in

Trishan Esram; Patrick L. Chapman

2007-01-01

12

Maximum power point tracker for a photovoltaic system  

Microsoft Academic Search

The need for renewable energy sources is on the rise because of the acute energy crisis in the world today. The main hindrance for the penetration and reach of solar PV system is its low efficiency and high capital cost. The output characteristics of photovoltaic arrays are nonlinear and change with the cell's temperature and solar radiation. Maximum power point

J. Suganya; M. Carolin Mabel

2012-01-01

13

Savannah River Site radioiodine atmospheric releases and offsite maximum doses  

SciTech Connect

Radioisotopes of iodine have been released to the atmosphere from the Savannah River Site since 1955. The releases, mostly from the 200-F and 200-H Chemical Separations areas, consist of the isotopes, I-129 and 1-131. Small amounts of 1-131 and 1-133 have also been released from reactor facilities and the Savannah River Laboratory. This reference memorandum was issued to summarize our current knowledge of releases of radioiodines and resultant maximum offsite doses. This memorandum supplements the reference memorandum by providing more detailed supporting technical information. Doses reported in this memorandum from consumption of the milk containing the highest I-131 concentration following the 1961 1-131 release incident are about 1% higher than reported in the reference memorandum. This is the result of using unrounded 1-131 concentrations of I-131 in milk in this memo. It is emphasized here that this technical report does not constitute a dose reconstruction in the same sense as the dose reconstruction effort currently underway at Hanford. This report uses existing published data for radioiodine releases and existing transport and dosimetry models.

Marter, W.L.

1990-11-01

14

Maximum power point tracking control of direct methanol fuel cells  

NASA Astrophysics Data System (ADS)

The performance of a direct methanol fuel cell (DMFC) is closely related to its operating conditions, and there is a specific combination of operating conditions at which the DMFC produces maximum power. Working at the maximum power point (MPP) can lower the methanol crossover rate and ancillary power consumption, improving the global efficiency of the system. The fuzzy controller proposed in this paper provides a simple and robust way to keep the DMFC working at the MPP by adjusting the operating conditions followed by the variation of the driven load in real time. Simulation shows that the fuzzy control approach can yield satisfactory results.

Zhang, Mingbo; Yan, Ting; Gu, Jinguang

2014-02-01

15

Predictive models for maximum recommended therapeutic dose of antiretroviral drugs.  

PubMed

A novel method for predicting maximum recommended therapeutic dose (MRTD) is presented using quantitative structure property relationships (QSPRs) and artificial neural networks (ANNs). MRTD data of 31 structurally diverse Antiretroviral drugs (ARVs) were collected from FDA MRTD Database or package inserts. Molecular property descriptors of each compound, that is, molecular mass, aqueous solubility, lipophilicity, biotransformation half life, oxidation half life, and biodegradation probability were calculated from their SMILES codes. A training set (n = 23) was used to construct multiple linear regression and back propagation neural network models. The models were validated using an external test set (n = 8) which demonstrated that MRTD values may be predicted with reasonable accuracy. Model predictability was described by root mean squared errors (RMSEs), Kendall's correlation coefficients (tau), P-values, and Bland Altman plots for method comparisons. MRTD was predicted by a 6-3-1 neural network model (RMSE = 13.67, tau = 0.643, P = 0.035) more accurately than by the multiple linear regression (RMSE = 27.27, tau = 0.714, P = 0.019) model. Both models illustrated a moderate correlation between aqueous solubility of antiretroviral drugs and maximum therapeutic dose. MRTD prediction may assist in the design of safer, more effective treatments for HIV infection. PMID:22481974

Branham, Michael Lee; Ross, Edward A; Govender, Thirumala

2012-01-01

16

Predictive Models for Maximum Recommended Therapeutic Dose of Antiretroviral Drugs  

PubMed Central

A novel method for predicting maximum recommended therapeutic dose (MRTD) is presented using quantitative structure property relationships (QSPRs) and artificial neural networks (ANNs). MRTD data of 31 structurally diverse Antiretroviral drugs (ARVs) were collected from FDA MRTD Database or package inserts. Molecular property descriptors of each compound, that is, molecular mass, aqueous solubility, lipophilicity, biotransformation half life, oxidation half life, and biodegradation probability were calculated from their SMILES codes. A training set (n = 23) was used to construct multiple linear regression and back propagation neural network models. The models were validated using an external test set (n = 8) which demonstrated that MRTD values may be predicted with reasonable accuracy. Model predictability was described by root mean squared errors (RMSEs), Kendall's correlation coefficients (tau), P-values, and Bland Altman plots for method comparisons. MRTD was predicted by a 6-3-1 neural network model (RMSE = 13.67, tau = 0.643, P = 0.035) more accurately than by the multiple linear regression (RMSE = 27.27, tau = 0.714, P = 0.019) model. Both models illustrated a moderate correlation between aqueous solubility of antiretroviral drugs and maximum therapeutic dose. MRTD prediction may assist in the design of safer, more effective treatments for HIV infection. PMID:22481974

Branham, Michael Lee; Ross, Edward A.; Govender, Thirumala

2012-01-01

17

Correcting for electron contamination at dose maximum in photon beams.  

PubMed

Data are presented to allow the photon beam quality specifier being used in the new AAPM TG-51 protocol, %dd(10)x, to be extracted from depth-dose data measured with a 1 mm lead foil either 50 cm or 30 cm from the phantom surface. %dd(10)x is the photon component of the percentage depth dose at 10 cm depth for a 10x10 cm2 field on the surface of a phantom at an SSD of 100 cm. The purpose of the foil is to remove the unknown electron contamination from the accelerator head. Monte Carlo calculations are done: (a) to show these electrons are reduced to a negligible level; (b) to calculate the amount of electron contamination from the lead foil at the depth of dose maximum; and (c) to calculate the effect of beam hardening on %dd(10). The analysis extends the earlier work of Li and Rogers [Med. Phys. 21, 791-798 (1994)] which only provided data for the foil at 50 cm. An error in the earlier Monte Carlo simulations is reported and a more convenient method of analyzing and using the data is presented. It is shown that 20% variations in the foil thickness have a negligible effect on the calculated corrections. PMID:10227355

Rogers, D W

1999-04-01

18

A nomogram for calculating the maximum dose of local anaesthetic.  

PubMed

Toxic dose limits (mg.kg(-1)) for local anaesthetics based on body weight are well-established, but calculation of the maximum safe volume (ml) of a given agent and formulation is complex, and frequently results in errors. We therefore developed a nomogram to perform this calculation. We compared the performance of the nomogram with a spreadsheet and a general purpose calculator using simulated clinical data. Bland-Altman analysis showed close agreement between the nomogram and spreadsheet, with bias of -0.07 ml and limits of agreement of -0.38 to +0.24 ml (correlation coefficient r(2) = 0.9980; p < 0.001). The nomogram produced fewer and smaller errors compared with the calculator. Our nomogram calculates the maximum safe volume (ml) of local anaesthetic to a clinically acceptable degree of accuracy. It facilitates rapid cross-checking of dosage calculations performed by electronic or other means at negligible cost, and can potentially reduce the incidence of local anaesthetic toxicity. PMID:24820093

Williams, D J; Walker, J D

2014-08-01

19

Preliminary estimates of the virtually safe dose for tumors obtained from the maximum tolerated dose  

SciTech Connect

The purpose of this paper was to examine the correlation between the maximum tolerated dose (MTD) and the low-dose estimate of the virtually safe dose (VSD) for animal carcinogens. Chronic bioassay results from the National Cancer Institute/National Toxicology Program carcinogenesis screening program were used. Estimates of the VSD were obtained by linear low-dose extrapolation for which an adequate dose-response relationship existed at the same tumor site in the same sex for both rats and mice. Estimates of the VSD were compared with the MTD for 69 tumor sites from 38 chemicals for rats and mice. The MTDs ranged from high to low toxicity (1 ppb to 4.4% in the diet). The overall geometric mean of the ratio of the MTD to the VSD corresponding to a maximum estimated risk of 10(-6) was 3.8 x 10(5). Of the 138 cases, only 3 cases were more than a factor of 10 from the mean ratio. This suggested that a quick estimate of the VSD could be obtained by dividing the MTD, obtained from a subchronic study, by 400,000. Further, if the human exposure is less than 10(-7) X MTD, the estimated risk is likely to be negligible even if the chemical is a carcinogen. It may not be worthwhile to conduct a chronic bioassay for the purpose of demonstrating a negligible risk, if the chemical is likely to be carcinogenic, unless the human exposure is extremely low.

Gaylor, D.W.

1989-04-01

20

A new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems  

Microsoft Academic Search

This paper presents a new algorithm for tracking maximum power point in photovoltaic systems. This is a fast tracking algorithm, where an initial approximation of maximum power point is (MPP) quickly achieved using a variable step-size. Subsequently, the exact maximum power point can be targeted using any conventional method like the hill-climbing or incremental conductance method. Thus, the drawback of

Sachin Jain; Vivek Agarwal

2004-01-01

21

Statistical Methods for Selecting Maximum Effective Dose and Evaluating Treatment Effect When Dose - Response is Monotonic  

PubMed Central

The maximum effective dose (MaxED) is an important quantity for therapeutic drugs. The MaxED for therapeutic drugs is defined as the dose above which no improvement in efficacy is obtained. In this article, we propose two experimental designs and analytic methods (one single-stage design and one two-stage design) to select the MaxED among several fixed doses and to compare the therapeutic effect of the selected MaxED with a control. The selection of MaxED is based on the isotonic regression under the restriction of monotonicity. In the single-stage design, both the selection of the MaxED and assessing its efficacy are carried out at the end of experiment. In the two-stage design, the selection of the MaxED and assessment of its efficacy are carried out at the interim analysis (first stage), the experiment in the second stage is carried out only at the selected MaxED and control if the first-stage test is not significant. Thus, the two-stage design enables selection of the MaxED at an earlier stage and stopping the trial earlier if the treatment effect at MaxED is extreme. Williams’ test (1972) is applied to test whether the selected MaxED is significantly different from control for the single-stage design and the first-stage test of the two-stage design. The sample size calculation for each design is provided. Extensive simulations are carried out to illustrate the performances of the proposed methods. PMID:25067994

Kong, Maiying; Rai, Shesh N.; Bolli, Roberto

2014-01-01

22

Power and Sample Size Determination for a Stepwise Test Procedure for Finding the Maximum Safe Dose  

E-print Network

Power and Sample Size Determination for a Stepwise Test Procedure for Finding the Maximum Safe Dose This paper addresses the problem of power and sample size calculation for a stepwise multiple test procedure functions, respectively. The sample sizes necessary on the zero dose control and each of the positive doses

Tamhane, Ajit C.

23

New approach to photovoltaic arrays maximum power point tracking  

Microsoft Academic Search

The present trend for commercial telecommunication and scientific satellites is the utilization of standard platform, characterized by a high level of flexibility and reduced nonrecurring costs. One of the areas where flexibility is mandatory is the electrical primary power subsystem, due to the impact on solar array configuration and dimensions and on power conditioning unit. Use of the maximum power

Angelo Brambilla; Marcello Gambarara; Antonio Garutti; F. Ronchi

1999-01-01

24

Topology Study of Photovoltaic Interface for Maximum Power Point Tracking  

Microsoft Academic Search

This paper looks at the performance of photovoltaic modules in nonideal conditions and proposes topologies to minimize the degradation of performance caused by these conditions. It is found that the peak power point of a module is significantly decreased due to only the slightest shading of the module, and that this effect is propagated through other nonshaded modules connected in

Weidong Xiao; Nathan Ozog; William G. Dunford

2007-01-01

25

maximum power point tracking in photovoltaic systems using model reference adaptive control.  

E-print Network

??This thesis proposes adaptive control architecture for maximum power point tracking (MPPT) in photovoltaic systems. Photovoltaic systems provide promising ways to generate clean electric power.… (more)

Zhang, Qinhao

2013-01-01

26

Development of an Analog Maximum Power Point Tracker for Photovoltaic Panel  

Microsoft Academic Search

Maximum power point trackers (MPPT) are used to operate a solar photovoltaic (PV) panel at its maximum power point (MPP). A number of tracking algorithms have been used in the past. A simple and cheap analog MPPT has been simulated and constructed. The MPP tracking algorithm is based on the fact that the MPP voltage is approximately a fixed percentage

A. Tariq; J. Asghar

2005-01-01

27

A sensorless control method for maximum power point tracking of wind turbine generators  

Microsoft Academic Search

Wind energy has been regarded as an environmentally friendly, logistically feasible and economically responsible alternative energy resource. In order to produce as much power as possible in variable speed wind turbine generators, the maximum power point tracking (MPPT) becomes a hotspot of research in this field. In this paper, a simple control method for maximum power point tracking (MPPT) in

Zhenyu Ma

2011-01-01

28

Maximum-Power-Point Tracking Method of Photovoltaic Using Only Single Current Sensor  

E-print Network

» «Solar cell systems» Abstract This paper describes a novel strategy of maximum-power-point trackingMaximum-Power-Point Tracking Method of Photovoltaic Using Only Single Current Sensor Toshihiko-2188, Japan Phone: +81-258-47-9510, Fax: +81-258-47-9500 e-mail: tnoguchi@vos.nagaokaut.ac.jp URL: pelab

Fujimoto, Hiroshi

29

Maximum Power Point Tracking Control for Photovoltaic System Using Adaptive Neuro-Fuzzy  

E-print Network

energy demand. The mathematical modeling and simulation of the photovoltaic system is implementedMaximum Power Point Tracking Control for Photovoltaic System Using Adaptive Neuro- Fuzzy "ANFIS) like ANFIS. This paper presents Maximum Power Point Tracking Control for Photovoltaic System Using

Paris-Sud XI, Université de

30

Maximum likelihood estimation of point scatterers in synthetic aperture radar data  

Microsoft Academic Search

The motivation for this research is the recognition of objects from the relative locations of radar point scatterers on the object. Point scatterers are modeled as damped exponential signals. Parametric estimation of the exponential parameters determines the point scatterer locations. Maximum likelihood estimation of exponential parameters in white Gaussian noise provides good results in many exponential estimation problems. In fact,

Matthew P. Pepin; Joseph J. Sacchini

1996-01-01

31

MAXINE: An improved methodology for estimating maximum individual dose from chronic atmospheric radioactive releases  

SciTech Connect

An EXCEL{reg_sign} spreadsheet has been developed that, when combined with the PC version of XOQDOQ, will generate estimates of maximum individual dose from routine atmospheric releases of radionuclides. The spreadsheet, MAXINE, utilizes a variety of atmospheric dispersion factors to calculate radiation dose as recommended by the US Nuclear Regulatory Commission in Regulatory Guide 1.109 [USNRC 1977a]. The methodology suggested herein includes use of both the MAXINE spreadsheet and the PC version of XOQDOQ.

Hamby, D.M.

1994-02-01

32

Microcontroller Servomotor for Maximum Effective Power Point for Solar Cell System  

E-print Network

In this paper a Maximum Power point (MPP) tracking algorithm is developed using dual-axis servomotor feedback tracking control system. An efficient and accurate servomotor system is used to increase the system efficiency and reduces the solar cell...

Al-Khalidy, M.; Al-Rawi, O.; Noaman, N.

2010-01-01

33

Submodule Integrated Distributed Maximum Power Point Tracking for Solar Photovoltaic Applications  

E-print Network

This paper explores the benefits of distributed power electronics in solar photovoltaic applications through the use of submodule integrated maximum power point trackers (MPPT). We propose a system architecture that provides ...

Pilawa-Podgurski, Robert C. N.

34

Variation of the peak temperature at the maximum as a function of dose in thermoluminescent phosphors  

NASA Astrophysics Data System (ADS)

A feature of the second and general-order kinetics equations is the shift of the peak temperature at the maximum towards lower temperatures as the dose increases. In this article, this effect is theoretically discussed. Some hypotheses are also given in order to explain this behaviour.

Favalli, A.; Furetta, C.; Cruz-Zaragoza, E.

2006-05-01

35

A fractional open circuit voltage based maximum power point tracker for photovoltaic arrays  

Microsoft Academic Search

In this paper a fractional open circuit voltage based maximum power point tracker (MPPT) for photovoltaic (PV) arrays is proposed. The fractional open circuit voltage based MPPT utilizes the fact that the PV array voltage corresponding to the maximum power exhibits a linear dependence with respect to array open circuit voltage for different irradiation and temperature levels. This method is

J. Ahmad

2010-01-01

36

A new maximum power point tracking control scheme for wind generation  

Microsoft Academic Search

According to the aerodynamical characteristic of the wind turbine, a maximum power point tracking (MPPT) is necessary to get high efficiency for wind power conversion, which means that the rotating speed of wind turbine should be adjusted in the real time to capture maximum wind power. Because of the fast variation of wind speed and the heavy inertia of generator,

Jia Yaoqin; Yang Zhongqing; Cao Binggang

2002-01-01

37

Novel maximum-power-point-tracking controller for photovoltaic energy conversion system  

Microsoft Academic Search

A novel maximum-power-point-tracking (MPPT) controller for a photovoltaic (PV) energy conversion system is presented. Using the slope of power versus voltage of a PV array, the proposed MPPT controller allows the conversion system to track the maximum power point very rapidly. As opposed to conventional two-stage designs, a single-stage configuration is implemented, resulting in size and weight reduction and increased

Yeong-Chau Kuo; Tsorng-Juu Liang; Jiann-Fuh Chen

2001-01-01

38

Design of Small Wind Turbine with Maximum Power Point Tracking Algorithm  

Microsoft Academic Search

This paper presents a complex design of Turbine with AC\\/DC converter containing Point Tracking Algorithm. The paper describes phenomenon and problems connected with designing particular parts for small wind turbine, such a generator addition, it shows short discussion between two different Maximum Power Point Tracking approaches experimental results.

M. Rolak; R. Kot; M. Malinowski; Z. Goryca; J. T. Szuster

2011-01-01

39

The new combined Maximum Power Point Tracking algorithm using fractional estimation in photovoltaic systems  

Microsoft Academic Search

This paper presents an improved algorithm of quick and accurate Maximum Power Point Tracking (MPPT) algorithm which is based on Incremental conductance algorithm, Fractional Open Circuit Voltage and Short Circuit Current. The proposed algorithm estimates the short circuit current or open circuit voltage, following by using Fractional Short Circuit Current or Fractional Open Circuit Voltage algorithm to quickly determine point

Dzung Phan Quoc; Quang Nguyen Nhat; Le Minh Phuong; Le Dinh Khoa; Nguyen Truong Dan Vu; Anh Nguyen Bao; Hong Hee Lee

2011-01-01

40

A novel maximum power point tracking algorithm for ocean wave energy devices  

Microsoft Academic Search

Many forms of renewable energy exist in the world's oceans, with ocean wave energy showing great potential. However, the ocean environment presents many challenges for cost-effective renewable energy conversion, including optimal control of a wave energy converter (WEC). This paper presents a novel maximum power point tracking (MPPT) algorithm for control of a point absorber WEC. The algorithm and control

Ean A. Amon; Alphonse A. Schacher; Ted K. A. Brekken

2009-01-01

41

The homeostatic set point of the hypothalamus-pituitary-thyroid axis – maximum curvature theory for personalized euthyroid targets  

PubMed Central

Background Despite rendering serum free thyroxine (FT4) and thyrotropin (TSH) within the normal population ranges broadly defined as euthyroidism, many patients being treated for hyperthyroidism and hypothyroidism persistently experience subnormal well-being discordant from their pre-disease healthy euthyroid state. This suggests that intra-individual physiological optimal ranges are narrower than laboratory-quoted normal ranges and implies the existence of a homeostatic set point encoded in the hypothalamic-pituitary-thyroid (HPT) axis that is unique to every individual. Methods We have previously shown that the dose–response characteristic of the hypothalamic-pituitary (HP) unit to circulating thyroid hormone levels follows a negative exponential curve. This led to the discovery that the normal reference intervals of TSH and FT4 fall within the ‘knee’ region of this curve where the maximum curvature of the exponential HP characteristic occurs. Based on this observation, we develop the theoretical framework localizing the position of euthyroid homeostasis over the point of maximum curvature of the HP characteristic. Results The euthyroid set points of patients with primary hypothyroidism and hyperthyroidism can be readily derived from their calculated HP curve parameters using the parsimonious mathematical model above. It can be shown that every individual has a euthyroid set point that is unique and often different from other individuals. Conclusions In this treatise, we provide evidence supporting a set point-based approach in tailoring euthyroid targets. Rendering FT4 and TSH within the laboratory normal ranges can be clinically suboptimal if these hormone levels are distant from the individualized euthyroid homeostatic set point. This mathematical technique permits the euthyroid set point to be realistically computed using an algorithm readily implementable for computer-aided calculations to facilitate precise targeted dosing of patients in this modern era of personalized medicine. PMID:25102854

2014-01-01

42

Use of iodine for water disinfection: iodine toxicity and maximum recommended dose.  

PubMed Central

Iodine is an effective, simple, and cost-efficient means of water disinfection for people who vacation, travel, or work in areas where municipal water treatment is not reliable. However, there is considerable controversy about the maximum safe iodine dose and duration of use when iodine is ingested in excess of the recommended daily dietary amount. The major health effect of concern with excess iodine ingestion is thyroid disorders, primarily hypothyroidism with or without iodine-induced goiter. A review of the human trials on the safety of iodine ingestion indicates that neither the maximum recommended dietary dose (2 mg/day) nor the maximum recommended duration of use (3 weeks) has a firm basis. Rather than a clear threshold response level or a linear and temporal dose-response relationship between iodine intake and thyroid function, there appears to be marked individual sensitivity, often resulting from unmasking of underlying thyroid disease. The use of iodine for water disinfection requires a risk-benefit decision based on iodine's benefit as a disinfectant and the changes it induces in thyroid physiology. By using appropriate disinfection techniques and monitoring thyroid function, most people can use iodine for water treatment over a prolonged period of time. PMID:10964787

Backer, H; Hollowell, J

2000-01-01

43

Maximum power point tracking parameter selection for higher order converters used in photovoltaic applications  

Microsoft Academic Search

Photovoltaic array needs an intermediate maximum power point trackers as their V-I characteristics are non-linear. Successful power tracking depends on the converter and its tracking parameters. The purpose of this investigation is to introduce a procedure for selection of the tracking parameters. To demonstrate the proposed approach a fourth order buck converter, belongs to higher order family, is chosen for

M. Veerachary

2009-01-01

44

Sensorless Maximum Power Point Tracking of Wind by DFIG Using Rotor Position Phase Lock Loop (PLL)  

Microsoft Academic Search

This paper presents an invention, the rotor position phase lock loop (PLL), which enables maximum power point (MPPT) tracking of wind by doubly-fed induction generators without needing a tachometer, an absolute position encoder, or an anemometer. The rotor position PLL is parameter variation insensitive, requiring only an estimate of the magnetization inductance for it to operate. It is also insensitive

Baike Shen; Bakari Mwinyiwiwa; Yongzheng Zhang; Boon-Teck Ooi

2009-01-01

45

A Novel Scheme for Rapid Tracking of Maximum Power Point in Wind Energy Generation Systems  

Microsoft Academic Search

This paper presents a novel maximum power point (MPP) tracking (MPPT) algorithm for grid-connected wind energy generation systems (WEGS). This is a rapid tracking algorithm that uses the fact that the value of ????,?? an intermediate variable, especially defined for the purpose, remains constant ( =??MPP ) for a given WEGS at the MPP irrespective of the wind velocity. The

Vivek Agarwal; Rakesh K. Aggarwal; Pravin Patidar; Chetan Patki

2010-01-01

46

Maximum likelihood estimations in a nonlinear self-exciting point process model  

Microsoft Academic Search

A nonlinear model generating a self-exciting point process is formulated and identification of the model using maximum likelihood estimations is discussed. Simulations have been performed and parameters are estimated numerically. (Dis)advantages with respect to identification approaches based on correlation densities are outlined. This method may function as a basis to interpret simultaneous recordings of single units in terms of underlying

H. van den Boogaard

1986-01-01

47

Review of the maximum power point tracking algorithms for stand-alone photovoltaic systems  

Microsoft Academic Search

A survey of the algorithms for seeking the maximum power point (MPP) is proposed. As has been shown, there are many ways of distinguishing and grouping methods that seek the MPP from a photovoltaic (PV) generator. However, in this article they are grouped as either direct or nondirect methods. The indirect methods (“quasi seeks”) have the particular feature that the

V. Salas; E. Olías; A. Barrado; A. Lázaro

2006-01-01

48

Performance of Photovoltaic Maximum Power Point Tracking Algorithms in the Presence of Noise  

E-print Network

Performance of Photovoltaic Maximum Power Point Tracking Algorithms in the Presence of Noise tracking (MPPT) algorithms for photovoltaic systems, including how noise affects both tracking speed-performance photovoltaic sys- tems. An intelligent controller adjusts the voltage, current, or impedance seen by a solar

Odam, Kofi

49

Evaluation of maximum power point tracking methods for grid connected photovoltaic systems  

Microsoft Academic Search

This paper presents a study of two maximum power point tracking methods for grid connected photovoltaic systems. The best operation conditions of the perturbation and observation and the incremental conductance are investigated in order to identify the performances of photovoltaic systems. Improvements of these methods can be obtained with the best adjustment of the sampling rate and the perturbation size.

G. M. S. Azevedo; M. C. Cavalcanti; K. C. Oliveira; F. A. S. Neves; Z. D. Lins

2008-01-01

50

Analysis and simulation of characteristics and maximum power point tracking for photovoltaic systems  

Microsoft Academic Search

The main purpose of this paper is to develop a photovoltaic simulation system with maximum power point tracking (MPPT) function using Matlab\\/Simulink software in order to simulate, evaluate and predict the behaviors of the real photovoltaic system. A model of the most important component in the photovoltaic system, the solar module, is the first to have been established. The characteristics

Ting-Chung Yu; Tang-Shiuan Chien

2009-01-01

51

A new fuzzy control method based on PSO for Maximum Power Point Tracking of photovoltaic system  

Microsoft Academic Search

Maximum Power Point Tracking (MPPT) is the key technology in the solar energy photovoltaic system, which plays an important role in enhancing energy utilization effectively. Aiming at problems existing in traditional fuzzy tracking method, such as pre-confirmation of control parameters, weak self-study ability, and effective tracking cannot be organized under the circumstance that the environment condition is changed greatly, a

Qiang Fu; Nan Tong

2011-01-01

52

Maximum tolerated dose versus metronomic scheduling in the treatment of metastatic cancers.  

PubMed

Although optimal control theory has been used for the theoretical study of anti-cancerous drugs scheduling optimization, with the aim of reducing the primary tumor volume, the effect on metastases is often ignored. Here, we use a previously published model for metastatic development to define an optimal control problem at the scale of the entire organism of the patient. In silico study of the impact of different scheduling strategies for anti-angiogenic and cytotoxic agents (either in monotherapy or in combination) is performed to compare a low-dose, continuous, metronomic administration scheme with a more classical maximum tolerated dose schedule. Simulation results reveal differences between primary tumor reduction and control of metastases but overall suggest use of the metronomic protocol. PMID:23850479

Benzekry, Sébastien; Hahnfeldt, Philip

2013-10-21

53

Maximum power point regulator for 4 kW solar cell array connected through invertor to the AC grid  

Microsoft Academic Search

A control system which allows the solar cell array (SCA) to operate at the maximum power point and to produce the maximum energy for any solar radiation is described. A control system is based on the maximum power point regulator (MPPR). The MPPR is designed to match a 4 kW SCA to a single phase bridge invertor. Operational principles of

Michael A. Slonim; Leo M. Rahovich

1996-01-01

54

Realworld maximum power point tracking simulation of PV system based on Fuzzy Logic control  

NASA Astrophysics Data System (ADS)

In the recent years, the solar energy becomes one of the most important alternative sources of electric energy, so it is important to improve the efficiency and reliability of the photovoltaic (PV) systems. Maximum power point tracking (MPPT) plays an important role in photovoltaic power systems because it maximize the power output from a PV system for a given set of conditions, and therefore maximize their array efficiency. This paper presents a maximum power point tracker (MPPT) using Fuzzy Logic theory for a PV system. The work is focused on the well known Perturb and Observe (P&O) algorithm and is compared to a designed fuzzy logic controller (FLC). The simulation work dealing with MPPT controller; a DC/DC ?uk converter feeding a load is achieved. The results showed that the proposed Fuzzy Logic MPPT in the PV system is valid.

Othman, Ahmed M.; El-arini, Mahdi M. M.; Ghitas, Ahmed; Fathy, Ahmed

2012-12-01

55

Development of a microcontroller-based, photovoltaic maximum power point tracking control system  

Microsoft Academic Search

Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC\\/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the

Eftichios Koutroulis; Kostas Kalaitzakis; Nicholas C. Voulgaris

2001-01-01

56

Subacute toxicity and maximum tolerable dose of sertaconazole in repeated administration studies.  

PubMed

28-Day oral and dermal subacute toxicity studies of 7-chloro-3-[1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl) ethoxy-methyl] benzo [b] thiophene (sertaconazole, FI-7045, CAS 99592-32-2), were carried out. The oral studies included the evaluation of subacute toxicity in rat (dose levels of 50, 150 and 300 mg/kg) and maximum tolerable dose in repeated administration in ferrets (consecutive dose levels in accordance with a geometric progression of 50, 75, 112.5, 168 and 250 mg/kg), which were the animal species intended for chronic toxicity studies. The dermal studies included the evaluation of subacute toxicity in rats and rabbits (1 ml/kg of a 2% cream). The results, in general, have shown low toxic effects, which can be summarized as a slight non-significant hepatomegalia in the rat with increased gamma-GTP and alkaline phosphatase values and a high urinary pH value; no histopathological changes were observed. These effects are characteristic of azole derivatives and are therefore common to other antifungals with this chemical group. PMID:1627193

Romero, A; Villamayor, F; Grau, M T; Sacristán, A; Ortíz, J A

1992-05-01

57

Locally weighted learning methods for predicting dose-dependent toxicity with application to the human maximum recommended daily dose.  

PubMed

Toxicological experiments in animals are carried out to determine the type and severity of any potential toxic effect associated with a new lead compound. The collected data are then used to extrapolate the effects on humans and determine initial dose regimens for clinical trials. The underlying assumption is that the severity of the toxic effects in animals is correlated with that in humans. However, there is a general lack of toxic correlations across species. Thus, it is more advantageous to predict the toxicological effects of a compound on humans directly from the human toxicological data of related compounds. However, many popular quantitative structure-activity relationship (QSAR) methods that build a single global model by fitting all training data appear inappropriate for predicting toxicological effects of structurally diverse compounds because the observed toxicological effects may originate from very different and mostly unknown molecular mechanisms. In this article, we demonstrate, via application to the human maximum recommended daily dose data that locally weighted learning methods, such as k-nearest neighbors, are well suited for predicting toxicological effects of structurally diverse compounds. We also show that a significant flaw of the k-nearest neighbor method is that it always uses a constant number of nearest neighbors in making prediction for a target compound, irrespective of whether the nearest neighbors are structurally similar enough to the target compound to ensure that they share the same mechanism of action. To remedy this flaw, we proposed and implemented a variable number nearest neighbor method. The advantages of the variable number nearest neighbor method over other QSAR methods include (1) allowing more reliable predictions to be achieved by applying a tighter molecular distance threshold and (2) automatic detection for when a prediction should not be made because the compound is outside the applicable domain. PMID:22963722

Liu, Ruifeng; Tawa, Gregory; Wallqvist, Anders

2012-10-15

58

Evaluation of Defined Daily Dose, percentage of British National Formulary maximum and chlorpromazine equivalents in antipsychotic drug utilization  

PubMed Central

Objective The present study was carried out to investigate and compare the three methods for calculating total antipsychotic dose among outpatients with schizophrenia attending primary psychiatric health care centers. The three methods were: Defined Daily Doses (DDDs), chlorpromazine equivalents (CPZeq) and percentages of the British National Formulary (BNF) maximum. Methodology Antipsychotic drug dosing data for 250 patients with schizophrenia were investigated by calculating Spearman’s rank correlation coefficients. Factors associated with antipsychotic dose, expressed as DDDs, CPZeq and percentages of the BNF maximum recommended daily dose, were investigated by means of linear regression analysis. Results Spearman’s correlation showed that there is a significant relationship between all pairs of the three dosing methods. In all three methods, coherence was strongest when dealing with first generation antipsychotics (FGA). Linear regression analyses showed a high degree of coherence between antipsychotic doses expressed as DDDs, CPZeq and percentages of the BNF maximum recommended daily dose. Conclusion All three tested methods are reliable and coherent for calculating antipsychotic dosing. PMID:24648824

Sweileh, Waleed M.; Odeh, Jihad Bani; Shraim, Naser Y.; Zyoud, Sa'ed H.; Sawalha, Ansam F.; Al-Jabi, Samah W.

2013-01-01

59

Unbounded Binary Search for a Fast and Accurate Maximum Power Point Tracking  

NASA Astrophysics Data System (ADS)

This paper presents a technique for maximum power point tracking (MPPT) of a concentrating photovoltaic system using cell level power optimization. Perturb and observe (P&O) has been a standard for an MPPT, but it introduces a tradeoff between the tacking speed and the accuracy of the maximum power delivered. The P&O algorithm is not suitable for a rapid environmental condition change by partial shading and self-shading due to its tracking time being linear to the length of the voltage range. Some of researches have been worked on fast tracking but they come with internal ad hoc parameters. In this paper, by using the proposed unbounded binary search algorithm for the MPPT, tracking time becomes a logarithmic function of the voltage search range without ad hoc parameters.

Kim, Yong Sin; Winston, Roland

2011-12-01

60

Active energy harvesting from microbial fuel cells at the maximum power point without using resistors.  

PubMed

Microbial fuel cell (MFC) technology offers a sustainable approach to harvest electricity from biodegradable materials. Energy production from MFCs has been demonstrated using external resistors or charge pumps, but such methods can only dissipate energy through heat or receive electrons passively from the MFC without any controllability. This study developed a new approach and system that can actively extract energy from MFC reactors at any operating point without using any resistors, especially at the peak power point to maximize energy production. Results show that power harvesting from a recirculating-flow MFC can be well maintained by the maximum power point circuit (MPPC) at its peak power point, while a charge pump was not able to change operating point due to current limitation. Within 18-h test, the energy gained from the MPPC was 76.8 J, 76 times higher than the charge pump (1.0 J) that was commonly used in MFC studies. Both conditions resulted in similar organic removal, but the Coulombic efficiency obtained from the MPPC was 21 times higher than that of the charge pump. Different numbers of capacitors could be used in the MPPC for various energy storage requirements and power supply, and the energy conversion efficiency of the MPPC was further characterized to identify key factors for system improvement. This active energy harvesting approach provides a new perspective for energy harvesting that can maximize MFC energy generation and system controllability. PMID:22486712

Wang, Heming; Park, Jae-Do; Ren, Zhiyong

2012-05-01

61

Magnification of starting torques of dc motors by maximum power point trackers in photovoltaic systems  

NASA Technical Reports Server (NTRS)

A calculation of the starting torque ratio of permanent magnet, series, and shunt-excited dc motors powered by solar cell arrays is presented for two cases, i.e., with and without a maximum-power-point tracker (MPPT). Defining motor torque magnification by the ratio of the motor torque with an MPPT to the motor torque without an MPPT, a magnification of 3 for the permanent magnet motor and a magnification of 7 for both the series and shunt motors are obtained. The study also shows that all motor types are less sensitive to solar insolation variation in systems including MPPTs as compared to systems without MPPTs.

Appelbaum, J.; Singer, S.

1989-01-01

62

A reliable, fast and low cost maximum power point tracker for photovoltaic applications  

SciTech Connect

This work presents a new maximum power point tracker system for photovoltaic applications. The developed system is an analog version of the ''P and O-oriented'' algorithm. It maintains its main advantages: simplicity, reliability and easy practical implementation, and avoids its main disadvantages: inaccurateness and relatively slow response. Additionally, the developed system can be implemented in a practical way at a low cost, which means an added value. The system also shows an excellent behavior for very fast variables in incident radiation levels. (author)

Enrique, J.M.; Andujar, J.M.; Bohorquez, M.A. [Departamento de Ingenieria Electronica, de Sistemas Informaticos y Automatica, Universidad de Huelva (Spain)

2010-01-15

63

Abstract--The many different techniques for maximum power point tracking of photovoltaic arrays are discussed. The  

E-print Network

Abstract--The many different techniques for maximum power point tracking of photovoltaic arrays on implementation. This manuscript should serve as a convenient reference for future work in photovoltaic power generation. Index Terms--maximum power point tracking, MPPT, photovoltaic, PV. I. INTRODUCTION RACKING

Chapman, Patrick

64

Correlation of Point B and Lymph Node Dose in 3D-Planned High-Dose-Rate Cervical Cancer Brachytherapy  

SciTech Connect

Purpose: To compare high dose rate (HDR) point B to pelvic lymph node dose using three-dimensional-planned brachytherapy for cervical cancer. Methods and Materials: Patients with FIGO Stage IB-IIIB cervical cancer received 70 tandem HDR applications using CT-based treatment planning. The obturator, external, and internal iliac lymph nodes (LN) were contoured. Per fraction (PF) and combined fraction (CF) right (R), left (L), and bilateral (Bil) nodal doses were analyzed. Point B dose was compared with LN dose-volume histogram (DVH) parameters by paired t test and Pearson correlation coefficients. Results: Mean PF and CF doses to point B were R 1.40 Gy +- 0.14 (CF: 7 Gy), L 1.43 +- 0.15 (CF: 7.15 Gy), and Bil 1.41 +- 0.15 (CF: 7.05 Gy). The correlation coefficients between point B and the D100, D90, D50, D2cc, D1cc, and D0.1cc LN were all less than 0.7. Only the D2cc to the obturator and the D0.1cc to the external iliac nodes were not significantly different from the point B dose. Significant differences between R and L nodal DVHs were seen, likely related to tandem deviation from irregular tumor anatomy. Conclusions: With HDR brachytherapy for cervical cancer, per fraction nodal dose approximates a dose equivalent to teletherapy. Point B is a poor surrogate for dose to specific nodal groups. Three-dimensional defined nodal contours during brachytherapy provide a more accurate reflection of delivered dose and should be part of comprehensive planning of the total dose to the pelvic nodes, particularly when there is evidence of pathologic involvement.

Lee, Larissa J. [Harvard Radiation Oncology Program, Brigham and Women's Hospital, Boston, MA (United States); Sadow, Cheryl A. [Department of Radiology, Brigham and Women's Hospital, Boston, MA (United States); Russell, Anthony [Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA (United States); Viswanathan, Akila N., E-mail: aviswanathan@lroc.harvard.ed [Department of Radiation Oncology, Brigham and Women's Hospital and Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA (United States)

2009-11-01

65

Experimental evaluation of actual delivered dose using mega-voltage cone-beam CT and direct point dose measurement  

SciTech Connect

Radiation therapy in patients is planned by using computed tomography (CT) images acquired before start of the treatment course. Here, tumor shrinkage or weight loss or both, which are common during the treatment course for patients with head-and-neck (H and N) cancer, causes unexpected differences from the plan, as well as dose uncertainty with the daily positional error of patients. For accurate clinical evaluation, it is essential to identify these anatomical changes and daily positional errors, as well as consequent dosimetric changes. To evaluate the actual delivered dose, the authors proposed direct dose measurement and dose calculation with mega-voltage cone-beam CT (MVCBCT). The purpose of the present study was to experimentally evaluate dose calculation by MVCBCT. Furthermore, actual delivered dose was evaluated directly with accurate phantom setup. Because MVCBCT has CT-number variation, even when the analyzed object has a uniform density, a specific and simple CT-number correction method was developed and applied for the H and N site of a RANDO phantom. Dose distributions were calculated with the corrected MVCBCT images of a cylindrical polymethyl methacrylate phantom. Treatment processes from planning to beam delivery were performed for the H and N site of the RANDO phantom. The image-guided radiation therapy procedure was utilized for the phantom setup to improve measurement reliability. The calculated dose in the RANDO phantom was compared to the measured dose obtained by metal-oxide-semiconductor field-effect transistor detectors. In the polymethyl methacrylate phantom, the calculated and measured doses agreed within about +3%. In the RANDO phantom, the dose difference was less than +5%. The calculated dose based on simulation-CT agreed with the measured dose within±3%, even in the region with a high dose gradient. The actual delivered dose was successfully determined by dose calculation with MVCBCT, and the point dose measurement with the image-guided radiation therapy procedure.

Matsubara, Kana, E-mail: matsubara-kana@hs.tmu.ac.jp [Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa-ku Tokyo (Japan); Kohno, Ryosuke [National Cancer Center Hospital East, Chiba (Japan); National Cancer Center Research Institute, Chiba (Japan); Nishioka, Shie; Shibuya, Toshiyuki; Ariji, Takaki; Akimoto, Tetsuo [National Cancer Center Hospital East, Chiba (Japan); Saitoh, Hidetoshi [Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa-ku Tokyo (Japan)

2013-07-01

66

Can point doses predict volumetric dose to rectum and bladder: a CT-based planning study in high dose rate intracavitary brachytherapy of cervical carcinoma?  

PubMed Central

Objective Point doses, as defined by the International Commission on Radiation Units and Measurements (ICRU), are classically used to evaluate doses to the rectum and bladder in high dose rate intracavitary brachytherapy (HDR-ICBT) in cervical cancer. Several studies have shown good correlation between the ICRU point doses and the volumetric doses to these organs. In the present study we attempted to evaluate whether this correlation could be used to predict the volumetric doses to these organs. Methods A total of 150 HDR-ICBT insertions performed between December 2006 and June 2008 were randomly divided into two groups. Group A (n=50) was used to derive the correlation between the point and volumetric doses using regression analysis. This was tested in Group B (n=100) insertions using studentised residuals and Bland–Altman plots. Results Significant correlations were obtained for all volumetric doses and ICRU point doses for rectum and bladder in Group A insertions. The strongest correlation was found for the dose to 2 cc volumes (D2cc). The correlation coefficients for bladder and rectal D2cc versus the respective ICRU point doses were 0.82 and 0.77, respectively (p<0.001). Statistical validation of equations generated in Group B showed mean studentised residual values of 0.001 and 0.000 for the bladder and rectum. However, Bland–Altman analysis showed that the error range for these equations for bladder and rectum were ±64% and ±41% of the point A dose, respectively, which makes these equations unreliable for clinical use. Conclusion Volumetric imaging is essential to obtain proper information about volumetric doses. PMID:21511749

Patil, V M; Patel, F D; Chakraborty, S; Oinam, A S; Sharma, S C

2011-01-01

67

Solar Panel System for Street Light Using Maximum Power Point Tracking (MPPT) Technique  

NASA Astrophysics Data System (ADS)

Solar energy is one form of the renewable energy which is very abundant in regions close to the equator. One application of solar energy is for street light. This research focuses on using the maximum power point tracking technique (MPPT), particularly the perturb and observe (P&O) algorithm, to charge battery for street light system. The proposed charger circuit can achieve 20.73% higher power efficiency compared to that of non-MPPT charger. We also develop the LED driver circuit for the system which can achieve power efficiency up to 91.9% at a current of 1.06 A. The proposed street lightning system can be implemented with a relatively low cost for public areas.

Wiedjaja, A.; Harta, S.; Josses, L.; Winardi; Rinda, H.

2014-03-01

68

Quality assurance for radiotherapy in prostate cancer: Point dose measurements in intensity modulated fields with large dose gradients  

SciTech Connect

Purpose: We aimed to evaluate an optimization algorithm designed to find the most favorable points to position an ionization chamber (IC) for quality assurance dose measurements of patients treated for prostate cancer with intensity-modulated radiotherapy (IMRT) and fields up to 10 cm x 10 cm. Methods and Materials: Three cylindrical ICs (PTW, Freiburg, Germany) were used with volumes of 0.6 cc, 0.125 cc, and 0.015 cc. Dose measurements were made in a plastic phantom (PMMA) at 287 optimized points. An algorithm was designed to search for points with the lowest dose gradient. Measurements were made also at 39 nonoptimized points. Results were normalized to a reference homogeneous field introducing a dose ratio factor, which allowed us to compare measured vs. calculated values as percentile dose ratio factor deviations {delta}F (%). A tolerance range of {delta}F (%) of {+-}3% was considered. Results: Half of the {delta}F (%) values obtained at nonoptimized points were outside the acceptable range. Values at optimized points were widely spread for the largest IC (i.e., 60% of the results outside the tolerance range), whereas for the two small-volume ICs, only 14.6% of the results were outside the tolerance interval. No differences were observed when comparing the two small ICs. Conclusions: The presented optimization algorithm is a useful tool to determine the best IC in-field position for optimal dose measurement conditions. A good agreement between calculated and measured doses can be obtained by positioning small volume chambers at carefully selected points in the field. Large chambers may be unreliable even in optimized points for IMRT fields {<=}10 cm x 10 cm.

Escude, Lluis [Servei de Radio-oncologia, Instituto Oncologico Teknon, Barcelona (Spain)]. E-mail: lluis.escude@gmx.net; Linero, Dolors [Servei de Radio-oncologia, Instituto Oncologico Teknon, Barcelona (Spain); Molla, Meritxell [Servei de Radio-oncologia, Instituto Oncologico Teknon, Barcelona (Spain); Miralbell, Raymond [Servei de Radio-oncologia, Instituto Oncologico Teknon, Barcelona (Spain); Service de Radio-oncologie, Hopitaux Universitaires, Geneva (Switzerland)

2006-11-15

69

The research on the algorithm of maximum power point tracking in photo voltaic array of solar car  

Microsoft Academic Search

Combined with the practical working environment of the vehicle photovoltaic cell plate on the electric vehicle, according to the engineering mathematic model of photovoltaic cell, the output characteristics is nonlinear, and the maximum power is on one point. Adopting the improved conductance increment method, the maximum power tracking rate and accuracy are enhanced.

Xiujuan Ma; Yude Sun; Jiayu Wu; Shiqiang Liu

2009-01-01

70

Long Duration Balloon Maximum Power Point Tracking (MPPT) solar power system development  

NASA Astrophysics Data System (ADS)

High altitude scientific balloons have been used for many years to provide scientists with access to near space at a fraction of the cost of satellite based or sounding rocket experiments. In recent years, these balloons have been successfully used for long duration missions of up to 40 days. Longer missions, with durations of up to 100 days (Ultra Long), are in the planning stages. Due to the flight durations, solar power systems have been utilized throughout the Long Duration Balloon (LDB) flight program to power the necessary electronic systems. Recently, Maximum Power Point Tracking (MPPT) charge controllers have become available off-the-shelf. These controllers along with high efficiency mono-crystalline solar cells have become reliable, low cost solutions even in the harsh environments they operate in. The LDB program at the Columbia Scientific Balloon Facility (CSBF) began supporting solar power systems with custom units fabricated by the Physical Science Laboratory (PSL) of New Mexico State University (NMSU). These charge controllers proved to be very reliable systems; however, they required intensive labor to build and were relatively expensive. As off-the-shelf MPPT charge controllers have become available, they have been integrated into the LDB flight support systems. Coupled with PSL developed interface electronics for monitoring and power switching, they have proven to be as reliable, less expensive, and more efficient. The addition of MPPT allows for the controller to operate the solar panel at it highest power production point. Newer, off-the-shelf controllers with smarter MPPT, are currently being tested. This paper describes the long and ultra-long balloon missions and the role that solar power plays in mission success. More importantly, it discusses the recent developments in off-the-shelf MPPT charge controllers configured for use in the harsh high altitude balloon environment.

Perez, Juan

71

Dose point kernel simulation for monoenergetic electrons and radionuclides using Monte Carlo techniques.  

PubMed

Monte Carlo (MC) simulation has been commonly used in the dose evaluation of radiation accidents and for medical purposes. The accuracy of simulated results is affected by the particle-tracking algorithm, cross-sectional database, random number generator and statistical error. The differences among MC simulation software packages must be validated. This study simulated the dose point kernel (DPK) and the cellular S-values of monoenergetic electrons ranging from 0.01 to 2 MeV and the radionuclides of (90)Y, (177)Lu and (103 m)Rh, using Fluktuierende Kaskade (FLUKA) and MC N-Particle Transport Code Version 5 (MCNP5). A 6-?m-radius cell model consisting of the cell surface, cytoplasm and cell nucleus was constructed for cellular S-value calculation. The mean absolute percentage errors (MAPEs) of the scaled DPKs, simulated using FLUKA and MCNP5, were 7.92, 9.64, 4.62, 3.71 and 3.84 % for 0.01, 0.1, 0.5, 1 and 2 MeV, respectively. For the three radionuclides, the MAPEs of the scaled DPKs were within 5 %. The maximum deviations of S(N?N), S(N?Cy) and S(N?CS) for the electron energy larger than 10 keV were 6.63, 6.77 and 5.24 %, respectively. The deviations for the self-absorbed S-values and cross-dose S-values of the three radionuclides were within 4 %. On the basis of the results of this study, it was concluded that the simulation results are consistent between FLUKA and MCNP5. However, there is a minor inconsistency for low energy range. The DPK and the cellular S-value should be used as the quality assurance tools before the MC simulation results are adopted as the gold standard. PMID:22923242

Wu, J; Liu, Y L; Chang, S J; Chao, M M; Tsai, S Y; Huang, D E

2012-11-01

72

Magnification of starting torques of dc motors by maximum power point trackers in photovoltaic systems  

NASA Technical Reports Server (NTRS)

Direct current (dc) motors are used in terrestrial photovoltaic (PV) systems such as in water-pumping systems for irrigation and water supply. Direct current motors may also be used for space applications. Simple and low weight systems including dc motors may be of special interest in space where the motors are directly coupled to the solar cell array (with no storage). The system will operate only during times when sufficient insolation is available. An important performance characteristic of electric motors is the starting to rated torque ratio. Different types of dc motors have different starting torque ratios. These ratios are dictated by the size of solar cell array, and the developed motor torque may not be sufficient to overcome the load starting torque. By including a maximum power point tracker (MPPT) in the PV system, the starting to rated torque ratio will increase, the amount of which depends on the motor type. The starting torque ratio is calculated for the permanent magnet, series and shunt excited dc motors when powered by solar cell arrays for two cases: with and without MPPT's. Defining a motor torque magnification by the ratio of the motor torque with an MPPT to the motor torque without an MPPT, a magnification of 3 was obtained for the permanent magnet motor and a magnification of 7 for both the series and shunt motors. The effect of the variation of solar insolation on the motor starting torque was covered. All motor types are less sensitive to insolation variation in systems including MPPT's as compared to systems with MPPT's. The analysis of this paper will assist the PV system designed to determine whether or not to include an MPPT in the system for a specific motor type.

Appelbaum, Joseph; Singer, S.

1989-01-01

73

Short-current pulse-based maximum-power-point tracking method for multiple photovoltaic-and-converter module system  

Microsoft Academic Search

This paper proposes a novel maximum-power-point tracking (MPPT) method with a simple algorithm for photovoltaic (PV) power generation systems. The method is based on use of a short-current pulse of the PV to determine an optimum operating current where the maximum output power can be obtained and completely differs from conventional hill-climbing-based methods. In the proposed system, the optimum operating

Toshihiko Noguchi; Shigenori Togashi; Ryo Nakamoto

2002-01-01

74

An overview of the report: Correlation between carcinogenic potency and the maximum tolerated dose: Implications for risk assessment  

SciTech Connect

Current practice in carcinogen bioassay calls for exposure of experimental animals at doses up to and including the maximum tolerated dose (MTD). Such studies have been used to compute measures of carcinogenic potency such as the TD[sub 50] as well as unit risk factors such as q[sub 1] for predicting low-dose risks. Recent studies have indicated that these measures of carcinogenic potency are highly correlated with the MTD. Carcinogenic potency has also been shown to be correlated with indicators of mutagenicity and toxicity. Correlation of the MTDs for rats and mice implies a corresponding correlation in TD[sub 50] values for these two species. The implications of these results for cancer risk assessment are examined in light of the large variation in potency among chemicals known to induce tumors in rodents. 119 refs., 2 figs., 4 tabs.

Krewski, D. (Health and Welfare Canada, Ottawa, Ontario (Canada) Carleton Univ. Ottawa, Ontario (Canada)); Gaylor, D.W. (National Center for Toxicological Research, Jefferson, AR (United States)); Soms, A.P. (Univ. of Wisconsin, Madison, WI (United States)); Szyszkowicz, M. (Health and Welfare Canada, Ottawa, Ontario (Canada))

1993-08-01

75

EPR spectrum deconvolution and dose assessment of fossil tooth enamel using maximum likelihood common factor analysis  

Microsoft Academic Search

In order to determine the components which give rise to the EPR spectrum around g = 2 we have applied Maximum Likelihood Common Factor Analysis (MLCFA) on the EPR spectra of enamel sample 1126 which has previously been analysed by continuous wave and pulsed EPR as well as EPR microscopy. MLCFA yielded agreeing results on three sets of X-band spectra

G. Vanhaelewyn; F. Callens; R. Grün

2000-01-01

76

Growing Neural Gas (GNG)Based Maximum Power Point Tracking for High-Performance Wind Generator With an Induction Machine  

Microsoft Academic Search

This paper presents a maximum power point track- ing (MPPT) technique for a high-performance wind generator with induction machine based on the growing neural gas (GNG) network. Here, a GNG network has been trained offline to learn the turbine characteristic surface torque versus wind speed and machine speed. It has been implemented online to perform the inversion of this function,

Maurizio Cirrincione; Marcello Pucci; Gianpaolo Vitale

2011-01-01

77

Hybrid Solar Photovoltaic\\/Wind Turbine Energy Generation System with Voltage-based Maximum Power Point Tracking  

Microsoft Academic Search

This article proposes a hybrid energy system combining solar photovoltaic and wind turbine as a small-scale alternative source of electrical energy where conventional generation is not practical. A simple and cost-effective control technique has been proposed for maximum power point tracking from the photovoltaic array and wind turbine under varying climatic conditions without measuring the irradiance of the photovoltaic or

Nabil A. Ahmed; Masafumi Miyatake; A. K. Al-Othman

2008-01-01

78

A Stand-Alone Hybrid Generation System Combining Solar Photovoltaic and Wind Turbine with Simple Maximum Power Point Tracking Control  

Microsoft Academic Search

This paper proposes a hybrid energy system combing solar photovoltaic and wind turbine as a small-scale alternative source of electrical energy where conventional generation is not practical. A simple and cost effective control technique has been proposed for maximum power point tracking from the photovoltaic array and wind turbine under varying climatic conditions without measuring the irradiance of the photovoltaic

Nabil A. Ahmed; Masafumi Miyatake

2006-01-01

79

Combination of Fuzzy-Based Maximum Power Point Tracker and Sun Tracker for Deployable Solar Panels in Photovoltaic Systems  

Microsoft Academic Search

Solar panels are power sources in photovoltaic applications. Solar panels I-V curves depend on environmental conditions such as irradiance, temperature, load and degradation level. In this paper, design and implementation of simultaneous fuzzy-based maximum power point tracker (MPPT) and sun tracker are presented for deployable solar panels. A digital controller was implemented by an AVR microcontroller. Results showed that the

Mohsen Taherbaneh; Hasan Ghafori Frard; Amir Hossein Rezaie; Shahab Karbasian

2007-01-01

80

Design & construction of microcontroller based maximum power point PWM charge controller for photovoltaic application  

Microsoft Academic Search

Photovoltaic cell converts solar energy directly into electricity. This paper describes a design of a charge controller to get the maximum power by using the Pulse Width Modulation (PWM) technique. In this paper PWM is controlled by the PIC Microcontroller. The work of the paper is to charge a 12 volt battery by using a 50 watt solar panel with

Gazi Mohammad Sharif; S. M. Mohaiminul Islam; Khosru Mohammad Salim

2009-01-01

81

Thermoelectric automotive waste heat energy recovery using maximum power point tracking  

Microsoft Academic Search

This paper proposes and implements a thermoelectric waste heat energy recovery system for internal combustion engine automobiles, including gasoline vehicles and hybrid electric vehicles. The key is to directly convert the heat energy from automotive waste heat to electrical energy using a thermoelectric generator, which is then regulated by a DC–DC ?uk converter to charge a battery using maximum power

Chuang Yu; K. T. Chau

2009-01-01

82

Real time estimation of photovoltaic modules characteristics and its application to maximum power point operation  

Microsoft Academic Search

In this paper, an approximate curve fitting method for photovoltaic modules is presented. The operation is based on solving a simple solar cell electrical model by a microcontroller in real time. Only four voltage and current coordinates are needed to obtain the solar module parameters and set its operation at maximum power in any conditions of illumination and temperature. Despite

Ausias Garrigós; José M. Blanes; José A. Carrasco; Juan B. Ejea

2007-01-01

83

Fuzzy Cognitive Networks for Maximum Power Point Tracking in Photovoltaic Arrays  

Microsoft Academic Search

\\u000a The studies on the photovoltaic (PV) power generation are extensively increasing, since it is considered as an essentially\\u000a inexhaustible and broadly available energy resource. However, the output power of the photovoltaic modules depends on solar\\u000a radiation and temperature of the solar cells. Therefore, to maximize the efficiency of the renewable energy system, it is\\u000a necessary to track the maximum power

Thodoris L. Kottas; Athanasios D. Karlis; Yiannis S. Boutalis

84

A DSP-based single-stage maximum power point tracking PV inverter  

Microsoft Academic Search

This paper presents the design and implementation of a DSP-based single-stage photovoltaic (PV) inverter system which can extract maximum power from solar panel. A perturbation and observation (P&O) method is realized and cooperated with a digital unipolar voltage switching sinusoidal pulse width modulation. The studied single-stage topology provides the benefits of low cost, simple configuration and good overall efficiency compared

Wen Long Yu; Ting-Peng Lee; Guan-Hong Wu; Qing Su Chen; Huang-Jen Chiu; Yu-Kang Lo; F. Shih

2010-01-01

85

Hybrid energy storage systems based on compressed air and supercapacitors with maximum efficiency point tracking  

Microsoft Academic Search

Beside the high-capacity storage facilities based on hydro-power technologies, electrochemical solutions are the today's candidate for storage for renewable energy sources. However, limited life-cycles and sustainability of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, based on compressed air energy storage (CAES). The storage and discharge are done within maximum efficiency

S. Lemofouet; A. Rufer

2005-01-01

86

A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter  

Microsoft Academic Search

A novel technique for efficiently extracting the maximum output power from a solar panel under varying meteorological conditions is presented. The methodology is based on connecting a pulse-width-modulated (PWM) DC\\/DC SEPIC or Cuk converter between a solar panel and a load or battery bus. The converter operates in discontinuous capacitor voltage mode whilst its input current is continuous. By modulating

Henry Shu-Hung Chung; K. K. Tse; S. Y. Ron Hui; C. M. Mok; M. T. Ho

2003-01-01

87

A Comparative Analysis of Low-Dose Metronomic Cyclophosphamide Reveals Absent or Low-Grade Toxicity on Tissues Highly Sensitive to the Toxic Effects of Maximum Tolerated Dose Regimens  

Microsoft Academic Search

The survival benefits of traditional maximum tolerated dose (MTD) cytotoxic therapy have been modest for the treatment of most types of metastatic malignancy and, moreover, often come with increased acute and chronic toxicity. Recent studies have demonstrated that the frequent administration of comparatively low doses of cytotoxic agents, with no extended breaks (low-dose metronomic (LDM) chemotherapy), may not only be

Urban Emmenegger; Shan Man; Yuval Shaked; Giulio Francia; John W. Wong; Daniel J. Hicklin; Robert S. Kerbel

2004-01-01

88

Calculation of dose decrease in a finite phantom of a {sup 192}Ir point source  

SciTech Connect

The purpose of this study was to calculate the dose decrease in a finite phantom of a {sup 192}Ir-point source by using a new algorithm based on field theory. The methods used included the phenomenological application of the principle 'mirror image of an electric point source in front of a dielectric semi-plateau' to a radioactive source in a finite phantom results in a function to calculate the dose decrease near the surface. Measurements were done in a water phantom in three different experimental setups. To verify the calculated results Monte Carlo (MC) simulations of dose distribution of a {sup 192}Ir point source in 34x40x40 cm{sup 3} water were carried out. The strength of mirror source was found -0.103 of the real source. A lack scatter function was necessary to handle the dose decrease very close to surface. The measured and calculated dose values differed less than 0.9%. Both MC simulations and the new algorithm show the dose decrease near phantom surface with differences less than 2% between each other. The new algorithm based on field theory calculated the dose decrease of a {sup 192}Ir point source in a finite phantom with a very good agreement to measured and simulated data. A clinical example, which affects only a single planar boundary, is given by using molds in the treatment of skin tumors. This was calculated with the new algorithm presented in this article. The comparison with the common algorithm demonstrates the differences that might cause an overestimation of the dose, which probably leads an underdosing of the tumor. The general use of the new algorithm in brachytherapy where a variety of boundary shapes are encountered has to be verified seriously.

Melchert, Corinna; Kohr, P.; Schmidt, R. [Department of Radiotherapy, University of Luebeck, Ratzeburger Allee 160, Luebeck, Schleswig-Holstein 23538 (Germany)

2007-10-15

89

Suitability of point kernel dose calculation techniques in brachytherapy treatment planning  

PubMed Central

Brachytherapy treatment planning system (TPS) is necessary to estimate the dose to target volume and organ at risk (OAR). TPS is always recommended to account for the effect of tissue, applicator and shielding material heterogeneities exist in applicators. However, most brachytherapy TPS software packages estimate the absorbed dose at a point, taking care of only the contributions of individual sources and the source distribution, neglecting the dose perturbations arising from the applicator design and construction. There are some degrees of uncertainties in dose rate estimations under realistic clinical conditions. In this regard, an attempt is made to explore the suitability of point kernels for brachytherapy dose rate calculations and develop new interactive brachytherapy package, named as BrachyTPS, to suit the clinical conditions. BrachyTPS is an interactive point kernel code package developed to perform independent dose rate calculations by taking into account the effect of these heterogeneities, using two regions build up factors, proposed by Kalos. The primary aim of this study is to validate the developed point kernel code package integrated with treatment planning computational systems against the Monte Carlo (MC) results. In the present work, three brachytherapy applicators commonly used in the treatment of uterine cervical carcinoma, namely (i) Board of Radiation Isotope and Technology (BRIT) low dose rate (LDR) applicator and (ii) Fletcher Green type LDR applicator (iii) Fletcher Williamson high dose rate (HDR) applicator, are studied to test the accuracy of the software. Dose rates computed using the developed code are compared with the relevant results of the MC simulations. Further, attempts are also made to study the dose rate distribution around the commercially available shielded vaginal applicator set (Nucletron). The percentage deviations of BrachyTPS computed dose rate values from the MC results are observed to be within plus/minus 5.5% for BRIT LDR applicator, found to vary from 2.6 to 5.1% for Fletcher green type LDR applicator and are up to ?4.7% for Fletcher-Williamson HDR applicator. The isodose distribution plots also show good agreements with the results of previous literatures. The isodose distributions around the shielded vaginal cylinder computed using BrachyTPS code show better agreement (less than two per cent deviation) with MC results in the unshielded region compared to shielded region, where the deviations are observed up to five per cent. The present study implies that the accurate and fast validation of complicated treatment planning calculations is possible with the point kernel code package. PMID:20589118

Lakshminarayanan, Thilagam; Subbaiah, K. V.; Thayalan, K.; Kannan, S. E.

2010-01-01

90

Maximum Principle of Optimal Control of the Primitive Equations of the Ocean with Two Point Boundary State Constraint  

SciTech Connect

We study in this article the Pontryagin's maximum principle for a class of control problems associated with the primitive equations (PEs) of the ocean with two point boundary state constraint. These optimal problems involve a two point boundary state constraint similar to that considered in Wang, Nonlinear Anal. 51, 509-536, 2002 for the three-dimensional Navier-Stokes (NS) equations. The main difference between this work and Wang, Nonlinear Anal. 51, 509-536, 2002 is that the nonlinearity in the PEs is stronger than in the three-dimensional NS systems.

Tachim Medjo, Theodore, E-mail: tachimt@fiu.ed [Florida International University, Department of Mathematics (United States)

2010-08-15

91

Implementation of maximum power point tracking using fuzzy logic controller for solar-powered light-flasher applications  

Microsoft Academic Search

This paper presents the development of maximum power point tracking (MPPT) using a fuzzy logic controller (FLC). By applying the synthetic fuzzy inference algorithm, the relation between input and output of FLC can be effectively stored in a memory-limited lookup table (LUT). As a consequence, the controller can be efficiently implemented on a low-cost 16F872 RISC microcontroller. A practical system

N. Khaehintung; P. Sirisuk

2004-01-01

92

On the maximum number of fixed points in automorphisms of prime order of 2(v; k; 1) designs  

E-print Network

). Further, for 3 Ÿ k Ÿ 5 and for any prime p j 1 mod k(k \\Gamma 1), we establish necessary and sufficient Ÿ 5 and for any prime p j 1 mod k(k \\Gamma 1), we establish necessary and sufficient conditions on vOn the maximum number of fixed points in automorphisms of prime order of 2­(v; k; 1) designs D. L

Stinson, Douglas

93

Theoretical and Experimental Analyses of Photovoltaic Systems with Voltage and Current-Based Maximum Power Point Tracking  

Microsoft Academic Search

Detailed theoretical and experimental analyses are presented for the comparison of two simple fast and reliable maximum power point tracking (MPPT) techniques for photovoltaic systems (PV): the voltage-based (VMPPT) and the current-based (CMPPT) approaches. A microprocessor-controlled tracker capable of online voltage and current measurements and programmed with both VMPPT and CMPPT algorithms is constructed. The load of the solar system

M. A. Masoum; H. Dehbonei; E. F. Fuchs

2002-01-01

94

Penetrative Rayleigh-Bénard convection in water near its maximum density point  

NASA Astrophysics Data System (ADS)

The presence of a density maximum in water near 4 °C significantly modifies the nature and onset conditions of convective flows due to imposed temperature differences. In the present study, vertical temperature gradients are imposed upon a horizontal, rectangular layer of water, with the top and bottom surfaces maintained above and below the maximum density temperature, respectively. In such an arrangement, convection beginning in the lower, unstable portion of the layer (as small as 1/3 of the layer height) may penetrate into the upper, stable region. The resulting convection patterns are visualized using schlieren or shadowgraph techniques along multiple visual axes. The measured onset conditions and observed patterns are discussed in the context of preceding predictions and experimental observations in similar penetrative systems. As expected from the non-Boussinesq nature of water in this temperature range, convection sets in at temperature differences below those predicted by linear stability theory when the unstable portion of the layer is sufficiently small. The conduction-convection transition is also hysteretic in nature. At onset, the convection pattern consists of parallel, transverse rolls due to the boundary conditions of the fluid chamber. When the unstable portion of the layer is significantly less than half of the fluid layer height, the convective motion is found to penetrate only partway into the upper stable region, within which weakly counter-rotating motions are driven. At higher Rayleigh numbers, the fluid undergoes secondary transitions to either hexagonal cellular or longitudinal roll states which are visualized for the first time. Pattern heights and wavenumbers were measured in some instances, establishing qualitative (in general) and quantitative (over some parameter ranges) agreement with linear theory.

Large, E.; Andereck, C. D.

2014-09-01

95

A Maximum Power Point Tracking Control Method of a Photovoltaic Power Generator with Consideration of Dynamic Characteristics of Solar Cells  

NASA Astrophysics Data System (ADS)

This paper discusses a new control strategy for photovoltaic power generation systems with consideration of dynamic characteristics of the photovoltaic cells. The controller estimates internal currents of an equivalent circuit for the cells. This estimated, or the virtual current and the actual voltage of the cells are fed to a conventional Maximum-Power-Point-Tracking (MPPT) controller. Consequently, this MPPT controller still tracks the optimum point even though it is so designed that the seeking speed of the operating point is extremely high. This system may suit for applications, which are installed in rapidly changeable insolation and temperature-conditions e.g. automobiles, trains, and airplanes. The proposed method is verified by experiment with a combination of this estimating function and the modified Boehringer's MPPT algorithm.

Watanabe, Takashi; Yoshida, Toshiya; Ohniwa, Katsumi

96

Maximum likelihood approach for the adaptive optics point spread function reconstruction  

NASA Astrophysics Data System (ADS)

This paper is dedicated to a new PSF reconstruction method based on a maximum likelihood approach (ML) which uses as well the telemetry data of the AO system (see Exposito et al. (2013)1). This approach allows a joint-estimation of the covariance matrix of the mirror modes of the residual phase, the noise variance and the Fried parameter r0. In this method, an estimate of the covariance between the parallel residual phase and the orthogonal phase is required. We developed a recursive approach taking into account the temporal effect of the AO-loop, so that this covariance only depends on the r0, the wind speed and some of the parameters of the system (the gain of the loop, the interaction matrix and the command matrix). With this estimation, the high bandwidth hypothesis is no longer required to reconstruct the PSF with a good accuracy. We present the validation of the method and the results on numerical simulations (on a SCAO system) and show that our ML method allows an accurate estimation of the PSF in the case of a Shack-Hartmann (SH) wavefront sensor (WFS).

Exposito, J.; Gratadour, Damien; Rousset, Gérard; Clénet, Yann; Mugnier, Laurent; Gendron, Éric

2014-08-01

97

Target point correction optimized based on the dose distribution of each fraction in daily IGRT  

NASA Astrophysics Data System (ADS)

Purpose: To use daily re-calculated dose distributions for optimization of target point corrections (TPCs) in image guided radiation therapy (IGRT). This aims to adapt fractioned intensity modulated radiation therapy (IMRT) to changes in the dose distribution induced by anatomical changes. Methods: Daily control images from an in-room on-rail spiral CT-Scanner of three head-and-neck cancer patients were analyzed. The dose distribution was re-calculated on each control CT after an initial TPC, found by a rigid image registration method. The clinical target volumes (CTVs) were transformed from the planning CT to the rigidly aligned control CTs using a deformable image registration method. If at least 95% of each transformed CTV was covered by the initially planned D95 value, the TPC was considered acceptable. Otherwise the TPC was iteratively altered to maximize the dose coverage of the CTVs. Results: In 14 (out of 59) fractions the criterion was already fulfilled after the initial TPC. In 10 fractions the TPC can be optimized to fulfill the coverage criterion. In 31 fractions the coverage can be increased but the criterion is not fulfilled. In another 4 fractions the coverage cannot be increased by the TPC optimization. Conclusions: The dose coverage criterion allows selection of patients who would benefit from replanning. Using the criterion to include daily re-calculated dose distributions in the TPC reduces the replanning rate in the analysed three patients from 76% to 59% compared to the rigid image registration TPC.

Stoll, Markus; Giske, Kristina; Stoiber, Eva M.; Schwarz, Michael; Bendl, Rolf

2014-03-01

98

Calculation of absorbed dose and biological effectiveness from photonuclear reactions in a bremsstrahlung beam of end point 50 MeV.  

PubMed

The absorbed dose due to photonuclear reactions in soft tissue, lung, breast, adipose tissue and cortical bone has been evaluated for a scanned bremsstrahlung beam of end point 50 MeV from a racetrack accelerator. The Monte Carlo code MCNP4B was used to determine the photon source spectrum from the bremsstrahlung target and to simulate the transport of photons through the treatment head and the patient. Photonuclear particle production in tissue was calculated numerically using the energy distributions of photons derived from the Monte Carlo simulations. The transport of photoneutrons in the patient and the photoneutron absorbed dose to tissue were determined using MCNP4B; the absorbed dose due to charged photonuclear particles was calculated numerically assuming total energy absorption in tissue voxels of 1 cm3. The photonuclear absorbed dose to soft tissue, lung, breast and adipose tissue is about (0.11-0.12)+/-0.05% of the maximum photon dose at a depth of 5.5 cm. The absorbed dose to cortical bone is about 45% larger than that to soft tissue. If the contributions from all photoparticles (n, p, 3He and 4He particles and recoils of the residual nuclei) produced in the soft tissue and the accelerator, and from positron radiation and gammas due to induced radioactivity and excited states of the nuclei, are taken into account the total photonuclear absorbed dose delivered to soft tissue is about 0.15+/-0.08% of the maximum photon dose. It has been estimated that the RBE of the photon beam of 50 MV acceleration potential is approximately 2% higher than that of conventional 60Co radiation. PMID:10495108

Gudowska, I; Brahme, A; Andreo, P; Gudowski, W; Kierkegaard, J

1999-09-01

99

Calculation of absorbed dose and biological effectiveness from photonuclear reactions in a bremsstrahlung beam of end point 50 MeV  

NASA Astrophysics Data System (ADS)

The absorbed dose due to photonuclear reactions in soft tissue, lung, breast, adipose tissue and cortical bone has been evaluated for a scanned bremsstrahlung beam of end point 50 MeV from a racetrack accelerator. The Monte Carlo code MCNP4B was used to determine the photon source spectrum from the bremsstrahlung target and to simulate the transport of photons through the treatment head and the patient. Photonuclear particle production in tissue was calculated numerically using the energy distributions of photons derived from the Monte Carlo simulations. The transport of photoneutrons in the patient and the photoneutron absorbed dose to tissue were determined using MCNP4B; the absorbed dose due to charged photonuclear particles was calculated numerically assuming total energy absorption in tissue voxels of 1 cm3. The photonuclear absorbed dose to soft tissue, lung, breast and adipose tissue is about (0.11-0.12)±0.05% of the maximum photon dose at a depth of 5.5 cm. The absorbed dose to cortical bone is about 45% larger than that to soft tissue. If the contributions from all photoparticles (n, p, 3He and 4He particles and recoils of the residual nuclei) produced in the soft tissue and the accelerator, and from positron radiation and gammas due to induced radioactivity and excited states of the nuclei, are taken into account the total photonuclear absorbed dose delivered to soft tissue is about 0.15±0.08% of the maximum photon dose. It has been estimated that the RBE of the photon beam of 50 MV acceleration potential is approximately 2% higher than that of conventional 60Co radiation.

Gudowska, I.; Brahme, A.; Andreo, P.; Gudowski, W.; Kierkegaard, J.

1999-09-01

100

Study of a thermoelectric system equipped with a maximum power point tracker for stand-alone electric generation.  

NASA Astrophysics Data System (ADS)

According to the International Energy Agency, 1.4 billion people are without electricity in the poorest countries and 2.5 billion people rely on biomass to meet their energy needs for cooking in developing countries. The use of cooking stoves equipped with small thermoelectric generator to provide electricity for basic needs (LED, cell phone and radio charging device) is probably a solution for houses far from the power grid. The cost of connecting every house with a landline is a lot higher than dropping thermoelectric generator in each house. Thermoelectric generators have very low efficiency but for isolated houses, they might become really competitive. Our laboratory works in collaboration with plane`te-bois (a non governmental organization) which has developed energy-efficient multifunction (cooking and hot water) stoves based on traditional stoves designs. A prototype of a thermoelectric generator (Bismuth Telluride) has been designed to convert a small part of the energy heating the sanitary water into electricity. This generator can produce up to 10 watts on an adapted load. Storing this energy in a battery is necessary as the cooking stove only works a few hours each day. As the working point of the stove varies a lot during the use it is also necessary to regulate the electrical power. An electric DC DC converter has been developed with a maximum power point tracker (MPPT) in order to have a good efficiency of the electronic part of the thermoelectric generator. The theoretical efficiency of the MMPT converter is discussed. First results obtained with a hot gas generator simulating the exhaust of the combustion chamber of a cooking stove are presented in the paper.

Favarel, C.; Champier, D.; Bédécarrats, J. P.; Kousksou, T.; Strub, F.

2012-06-01

101

A proposed adaptive step size perturbation and observation maximum power point tracking algorithm based on photovoltaic system modeling  

NASA Astrophysics Data System (ADS)

Solar energy becomes one of the major alternative renewable energy options for its huge abundance and accessibility. Due to the intermittent nature, the high demand of Maximum Power Point Tracking (MPPT) techniques exists when a Photovoltaic (PV) system is used to extract energy from the sunlight. This thesis proposed an advanced Perturbation and Observation (P&O) algorithm aiming for relatively practical circumstances. Firstly, a practical PV system model is studied with determining the series and shunt resistances which are neglected in some research. Moreover, in this proposed algorithm, the duty ratio of a boost DC-DC converter is the object of the perturbation deploying input impedance conversion to achieve working voltage adjustment. Based on the control strategy, the adaptive duty ratio step size P&O algorithm is proposed with major modifications made for sharp insolation change as well as low insolation scenarios. Matlab/Simulink simulation for PV model, boost converter control strategy and various MPPT process is conducted step by step. The proposed adaptive P&O algorithm is validated by the simulation results and detail analysis of sharp insolation changes, low insolation condition and continuous insolation variation.

Huang, Yu

102

Dose response study of ipratropium bromide aerosol on maximum exercise performance in stable patients with chronic obstructive pulmonary disease  

Microsoft Academic Search

BACKGROUND: Although the bronchodilating effect of inhaled anticholinergics has been established in patients with chronic obstructive pulmonary disease (COPD), their effects on exercise capacity are still controversial. Previous studies have suggested that the standard dosage hardly affects exercise tolerance, whereas higher doses might elicit an improvement. The aim of the present study was to determine the dose of ipratropium bromide

A. Ikeda; K. Nishimura; H. Koyama; M. Tsukino; M. Mishima; T. Izumi

1996-01-01

103

Methodology used to compute maximum potential doses from ingestion of edible plants and wildlife found on the Hanford Site  

SciTech Connect

The purpose of this report is to summarize the assumptions, dose factors, consumption rates, and methodology used to evaluate potential radiation doses to persons who may eat contaminated wildlife or contaminated plants collected from the Hanford Site. This report includes a description of the number and variety of wildlife and edible plants on the Hanford Site, methods for estimation of the quantities of these items consumed and conversion of intake of radionuclides to radiation doses, and example calculations of radiation doses from consumption of plants and wildlife. Edible plants on the publicly accessible margins of the shoreline of the Hanford Site and Wildlife that move offsite are potential sources of contaminated food for the general public. Calculations of potential radiation doses from consumption of agricultural plants and farm animal products are made routinely and reported annually for those produced offsite, using information about concentrations of radionuclides, consumption rates, and factors for converting radionuclide intake into dose. Dose calculations for onsite plants and wildlife are made intermittently when appropriate samples become available for analysis or when special studies are conducted. Consumption rates are inferred from the normal intake rates of similar food types raised offsite and from the edible weight of the onsite product that is actually available for harvest. 19 refs., 4 tabs.

Soldat, J.K.; Price, K.R.; Rickard, W.H.

1990-10-01

104

A Signal-to-Noise Crossover Dose as the Point of Departure for Health Risk Assessment  

PubMed Central

Background: The U.S. National Toxicology Program (NTP) cancer bioassay database provides an opportunity to compare both existing and new approaches to determining points of departure (PoDs) for establishing reference doses (RfDs). Objectives: The aims of this study were a) to investigate the risk associated with the traditional PoD used in human health risk assessment [the no observed adverse effect level (NOAEL)]; b) to present a new approach based on the signal-to-noise crossover dose (SNCD); and c) to compare the SNCD and SNCD-based RfD with PoDs and RfDs based on the NOAEL and benchmark dose (BMD) approaches. Methods: The complete NTP database was used as the basis for these analyses, which were performed using the Hill model. We determined NOAELs and estimated corresponding extra risks. Lower 95% confidence bounds on the BMD (BMDLs) corresponding to extra risks of 1%, 5%, and 10% (BMDL01, BMDL05, and BMDL10, respectively) were also estimated. We introduce the SNCD as a new PoD, defined as the dose where the additional risk is equal to the “background noise” (the difference between the upper and lower bounds of the two-sided 90% confidence interval on absolute risk) or a specified fraction thereof. Results: The median risk at the NOAEL was approximately 10%, and the default uncertainty factor (UF = 100) was considered most applicable to the BMDL10. Therefore, we chose a target risk of 1/1,000 (0.1/100) to derive an SNCD-based RfD by linear extrapolation. At the median, this approach provided the same RfD as the BMDL10 divided by the default UF. Conclusions: Under a standard BMD approach, the BMDL10 is considered to be the most appropriate PoD. The SNCD approach, which is based on the lowest dose at which the signal can be reliably detected, warrants further development as a PoD for human health risk assessment. PMID:21813365

Portier, Christopher J.; Krewski, Daniel

2011-01-01

105

Maximum tolerated doses of methotrexate and 7-hydroxy-methotrexate in a model of acute toxicity in rats  

Microsoft Academic Search

Purpose: After more than 50?years of methotrexate (MTX) treatment of acute lymphoblastic leukaemia (ALL), it is currently believed\\u000a that as long as dose escalations are followed by adequate leucovorin rescue guided by monitoring MTX serum concentrations,\\u000a hydration and urinary alkalinization, high-dose MTX (HD-MTX) can be tolerated without life-threatening toxicity. However,\\u000a our recent experimental animal studies of the major metabolite of

Ole-Martin Fuskevåg; Christel Kristiansen; Sigurd Lindal; Jarle Aarbakke

2000-01-01

106

Self-absorption correction for 32P, 198Au and 188Re stents: dose point kernel calculations versus Monte Carlo.  

PubMed

Monte Carlo simulations of dose distributions around radioactive stents are very time intensive. Thus, in order to calculate the dose distribution around a 188Re stent, we chose to test a point kernel method, a method which is known to be faster but the accuracy of which has not been established for this application. The dose point kernel method, which takes into account absorption in the strut material (=self-absorption), was based on different beta-emitting point source distributions in water by itself and surrounded by steel spheres of different thicknesses. This information was input into an integration routine that modeled either a Palmaz-Schatz or Multilink stent. The dose distributions around 198Au and 32P stents calculated with the dose point kernel method were compared to those calculated using EGS4 and MCNP 4B Monte Carlo methods. The resulting correction for self-absorption in steel was distance dependent and averaged 1.12 for 32P and 1.25 for 198Au stents. The dose point kernel method gave nearly identical results to these full Monte Carlo simulations and was thus used to calculate the dose distributions around a 188Re stent. Although 188Re has a half-life of only 17 hours, it is posited to be useful for radioactive restenosis prevention, given that a recently developed rapid electrodeposition procedure allows stents to be made radioactive, at predetermined activities, within 15 minutes. The dose point kernel calculations of a 188Re-coated Multilink stent were compared to its radiochromic film measurements. The dose fall-off agreed with the calculations within 5% over 0.4 to 3.5 mm from the stent surface. The dose point kernel method is a valuable tool to determine depth dose distributions around activated stents taking into account the detailed geometry and the self-absorption in the struts. It not only requires much less processing time than Monte Carlo methods, but also allows the use of higher resolutions in modeling the geometry, which leads to more accurate self-absorption correction factors. PMID:11585219

Reynaert, N; Häfeli, U O

2001-09-01

107

Neural-network-based maximum-power-point tracking of coupled-inductor interleaved-boost-converter-supplied PV system using fuzzy controller  

Microsoft Academic Search

The photovoltaic (PV) generator exhibits a nonlinear V-I characteristic and its maximum power (MP) point varies with solar insolation. In this paper, a feedforward MP-point tracking scheme is developed for the coupled-inductor interleaved-boost-converter-fed PV system using a fuzzy controller. The proposed converter has lower switch current stress and improved efficiency over the noncoupled converter system. For a given solar insolation,

Mummadi Veerachary; Tomonobu Senjyu; Katsumi Uezato

2003-01-01

108

Review and critical analysis of the research papers published till date on maximum power point tracking in wind energy conversion system  

Microsoft Academic Search

Maximum power point tracking (MPPT) is a very important necessity in a system of energy conversion from a renewable energy source. Every year a number of publications appear in various journals and conferences claiming to offer better and faster MPPT techniques for wind energy conversion system (WECS). This research paper provides a concise yet comprehensive critical analysis of these techniques

Syed Muhammad Raza Kazmi; Hiroki Goto; Hai-Jiao Guo; Osamu Ichinokura

2010-01-01

109

New Maximum Power Point Tracker Using Sliding-Mode Observer for Estimation of Solar Array Current in the Grid-Connected Photovoltaic System  

Microsoft Academic Search

A new maximum power point tracker (MPPT) for a grid-connected photovoltaic system without solar array current sensor is proposed. The solar array current information is obtained from the sliding-mode observer and fed into the MPPT to generate the reference voltage. The parameter values such as capacitances can be changed up to 50% from their nominal values, and the linear observer

Il-Song Kim; Myung-Bok Kim; Myung-Joong Youn

2006-01-01

110

Cascaded H-bridge multilevel converter for grid connected photovoltaic generators with independent maximum power point tracking of each solar array  

Microsoft Academic Search

This paper introduces a new control method and proportional PWM modulation of the cascaded H-bridge multilevel converter for grid-connected photovoltaic systems. This control makes each H-bridge module supply different power levels, allowing therefore for each module an independent maximum power point tracking of the corresponding photovoltaic array.

O. Alonso; P. Sanchis; E. Gubia; L. Marroyo

2003-01-01

111

An open-label study to determine the maximum tolerated dose of the multitargeted tyrosine kinase inhibitor CEP-11981 in patients with advanced cancer.  

PubMed

Background This phase I study evaluated the pharmacokinetics and pharmacodynamics of CEP-11981, an oral vascular endothelial growth factor (VEGF) tyrosine kinase inhibitor, in patients with advanced, relapsed, or refractory solid tumors. Methods Oral CEP-11981 dose escalations followed a modified Fibonacci sequence (from 3.0 to 4.2, 5.9, 11.8, 19.7, 29.6, 41.4, 55.0, 73.0, 97.4, and 126.6 mg/m(2)). The maximum-tolerated dose (MTD), dose-limiting toxicities (DLTs), tumor response, and safety were evaluated. Results CEP-11981 was tolerated at doses between 3.0 and 97.4 mg/m(2). The MTD of CEP-11981 was determined to be 97.4 mg/m(2), with DLTs observed at the 126.6 mg/m(2) dose. The DLTs were grade 4 neutropenia in 1 patient and grade 3 T-wave inversion with chest heaviness and fatigue in 1 patient. All 3 events resolved on stopping CEP-11981. The most frequently reported adverse events of any grade were fatigue, nausea, diarrhea, decreased appetite, abdominal pain, back pain, vomiting, constipation, headache, dizziness, and dyspnea. Treatment-related grade 3/4 neutropenia was observed in the highest-dose cohorts (2 patients at 97.4 mg/m(2) and 1 patient at 126.6 mg/m(2)), indicating some off-target inhibition. VEGF inhibition was greatest in the higher-dose groups. Although no patient experienced complete or partial response, 44 % patients achieved stable disease when measured at ??6 weeks, which occurred more frequently in cohorts receiving ??73.0 mg/m(2). Conclusions In patients with recurrent or refractory solid tumors, disease stabilization was achieved. Despite acceptable tolerability of CEP-11981 at the MTD, further development by the sponsor has ceased. PMID:25152243

Pili, Roberto; Carducci, Michael; Brown, Peter; Hurwitz, Herbert

2014-12-01

112

Approach to calculating upper bounds on maximum individual doses from the use of contaminated well water following a WIPP repository breach. Report EEG-9  

SciTech Connect

As part of the assessment of the potential radiological consequences of the proposed Waste Isolation Pilot Plant (WIPP), this report evaluates the post-closure radiation dose commitments associated with a possible breach event which involves dissolution of the repository by groundwaters and subsequent transport of the nuclear waste through an aquifer to a well assumed to exist at a point 3 miles downstream from the repository. The concentrations of uranium and plutonium isotopes at the well are based on the nuclear waste inventory presently proposed for WIPP and basic assumptions concerning the transport of waste as well as treatment to reduce the salinity of the water. The concentrations of U-233, Pu-239, and Pu-240, all radionuclides originally emplaced as waste in the repository, would exceed current EPA drinking water limits. The concentrations of U-234, U-235, and U-236, all decay products of plutonium isotopes originally emplaced as waste, would be well below current EPA drinking water limits. The 50-year dose commitments from one year of drinking treated water contaminated with U-233 or Pu-239 and Pu-240 were found to be comparable to a one-year dose from natural background. The 50-year dose commitments from one year of drinking milk would be no more than about 1/5 the dose obtained from ingestion of treated water. These doses are considered upper bounds because of several very conservative assumptions which are discussed in the report.

Spiegler, P.

1981-09-01

113

Calculation of electron and isotopes dose point kernels with fluka Monte Carlo code for dosimetry in nuclear medicine therapy  

SciTech Connect

Purpose: The calculation of patient-specific dose distribution can be achieved by Monte Carlo simulations or by analytical methods. In this study, fluka Monte Carlo code has been considered for use in nuclear medicine dosimetry. Up to now, fluka has mainly been dedicated to other fields, namely high energy physics, radiation protection, and hadrontherapy. When first employing a Monte Carlo code for nuclear medicine dosimetry, its results concerning electron transport at energies typical of nuclear medicine applications need to be verified. This is commonly achieved by means of calculation of a representative parameter and comparison with reference data. Dose point kernel (DPK), quantifying the energy deposition all around a point isotropic source, is often the one. Methods: fluka DPKs have been calculated in both water and compact bone for monoenergetic electrons (10{sup -3} MeV) and for beta emitting isotopes commonly used for therapy ({sup 89}Sr, {sup 90}Y, {sup 131}I, {sup 153}Sm, {sup 177}Lu, {sup 186}Re, and {sup 188}Re). Point isotropic sources have been simulated at the center of a water (bone) sphere, and deposed energy has been tallied in concentric shells. fluka outcomes have been compared to penelope v.2008 results, calculated in this study as well. Moreover, in case of monoenergetic electrons in water, comparison with the data from the literature (etran, geant4, mcnpx) has been done. Maximum percentage differences within 0.8{center_dot}R{sub CSDA} and 0.9{center_dot}R{sub CSDA} for monoenergetic electrons (R{sub CSDA} being the continuous slowing down approximation range) and within 0.8{center_dot}X{sub 90} and 0.9{center_dot}X{sub 90} for isotopes (X{sub 90} being the radius of the sphere in which 90% of the emitted energy is absorbed) have been computed, together with the average percentage difference within 0.9{center_dot}R{sub CSDA} and 0.9{center_dot}X{sub 90} for electrons and isotopes, respectively. Results: Concerning monoenergetic electrons, within 0.8{center_dot}R{sub CSDA} (where 90%-97% of the particle energy is deposed), fluka and penelope agree mostly within 7%, except for 10 and 20 keV electrons (12% in water, 8.3% in bone). The discrepancies between fluka and the other codes are of the same order of magnitude than those observed when comparing the other codes among them, which can be referred to the different simulation algorithms. When considering the beta spectra, discrepancies notably reduce: within 0.9{center_dot}X{sub 90}, fluka and penelope differ for less than 1% in water and less than 2% in bone with any of the isotopes here considered. Complete data of fluka DPKs are given as Supplementary Material as a tool to perform dosimetry by analytical point kernel convolution. Conclusions: fluka provides reliable results when transporting electrons in the low energy range, proving to be an adequate tool for nuclear medicine dosimetry.

Botta, F.; Mairani, A.; Battistoni, G.; Cremonesi, M.; Di Dia, A.; Fasso, A.; Ferrari, A.; Ferrari, M.; Paganelli, G.; Pedroli, G.; Valente, M. [Medical Physics Department, European Institute of Oncology, Via Ripamonti 435, 20141 Milan (Italy); Istituto Nazionale di Fisica Nucleare (I.N.F.N.), Via Celoria 16, 20133 Milan (Italy); Medical Physics Department, European Institute of Oncology, Via Ripamonti 435, 20141 Milan (Italy); Jefferson Lab, 12000 Jefferson Avenue, Newport News, Virginia 23606 (United States); CERN, 1211 Geneva 23 (Switzerland); Medical Physics Department, European Institute of Oncology, Milan (Italy); Nuclear Medicine Department, European Institute of Oncology, Via Ripamonti 435, 2014 Milan (Italy); Medical Physics Department, European Institute of Oncology, Via Ripamonti 435, 20141 Milan (Italy); FaMAF, Universidad Nacional de Cordoba and CONICET, Cordoba, Argentina C.P. 5000 (Argentina)

2011-07-15

114

A Single Cell Maximum Power Point Tracking Converter without a Current Sensor for High Performance Vehicle Solar Arrays  

Microsoft Academic Search

A maximum power tracker is developed for a single high performance GaAs solar cell to reduce the impact of variations in cell illumination for highly curved arrays as required for vehicle applications. This solution also finds applications in concentrating photovoltaic systems where the incident energy may vary due to optical imperfections. On a curved array, each cell has a directly

P. J. Wolfs; L. Tang

2005-01-01

115

Biocompatibility of antimicrobials to maggot debridement therapy: medical maggots Lucilia sericata (Diptera: Calliphoridae) exhibit tolerance to clinical maximum doses of antimicrobials.  

PubMed

The larvae of calliphorid flies are used to debride wounds of patients with severe tissue destruction, often concurrently with antimicrobials. The current study evaluates the effects of ceftazidime, tobramycin, amikacin, gentamicin, polymyxin B, doxycycline, paromomycin, amphotericin B, sodium stibogluconate, and miltefosine at 1, 10, and 100 x the Maximum Clinical Concentration (mg/kg/d) in raw liver assays. Effects on larvae were small and depended on dose and antimicrobial formulation, with hours in assay (24 or 48 h) having a significant effect on larval survival. Sodium stibgluconate had the strongest effect on maggot survival (80.0% at 48 h). These results suggest that the antimicrobials tested here may be used simultaneously with maggot debridement therapy, and may actually increase the effectiveness of maggot debridement therapy in certain applications where >1 x Maximum Clinical Concentration is indicated, such as topical creams for cutaneous leishmaniasis. PMID:23025196

Peck, George W; Kirkup, Benjamin C

2012-09-01

116

A two-dimensional point-kernel model for dose calculations in a glove-box array  

SciTech Connect

An associated paper details a model of a room containing glove boxes using the industry standard dose equivalent (dose) estimation tool MCNP. Such tools provide an excellent means for obtaining relatively reliable estimates of radiation transport in a complicated geometric structure. However, creating the input deck that models the complicated geometry is equally complicated. Therefore, an alternative tool is desirable that provides reasonably accurate dose estimates in complicated geometries for use in engineering-scale dose analyses. In the past, several tools that use the point-kernel model for estimating doses equivalent have been constructed (those referenced are only a small sample of similar tools). This new tool, the Photon And Neutron Dose Equivalent Model Of Nuclear materials Integrated with an Uncomplicated geometry Model (PANDEMONIUM), combines point-kernel and diffusion theory calculation routines with a geometry construction tool. PANDEMONIUM uses Visio to draw a glove-box array in the room, including hydrogenous shields, sources, and detectors. This simplification in geometric rendering limits the tool to two-dimensional geometries (and one-dimensional particle transport calculations).

Kornreich, D.E.; Dooley, D.E.

1999-07-01

117

A close-form solution for the maximum-power operating point of a solar cell array  

Microsoft Academic Search

A solar cell array is inherently a nonlinear device consisting of several solar cell modules connected in series-parallel combinations to provide the desired DC voltage and current. At a fixed insolation level, the terminal voltage decreases nonlinearly as the load current increases. Due to this nonlinearity, it is difficult to determine analytically the operating point at which the output power

S. M. Alghuwainem

1997-01-01

118

Development of a novel multi-point plastic scintillation detector with a single optical transmission line for radiation dose measurement*  

PubMed Central

Purpose The goal of this study was to develop a novel multi-point plastic scintillation detector (mPSD) capable of measuring the dose accurately at multiple positions simultaneously using a single optical transmission line. Methods A 2-point mPSD used a band-pass approach that included splitters, color filters, and an EMCCD camera. The 3-point mPSD was based on a new full-spectrum approach, in which a spectrograph was coupled to a CCD camera. Irradiations of the mPSDs and of an ion chamber were performed with a 6-MV photon beam at various depths and lateral positions in a water tank. Results For the 2-point mPSD, the average relative differences between mPSD and ion chamber measurements for the depth-dose were 2.4±1.6% and 1.3±0.8% for BCF-60 and BCF-12, respectively. For the 3-point mPSD, the average relative differences over all conditions were 2.3±1.1%, 1.6±0.4%, and 0.32±0.19% for BCF-60, BCF-12, and BCF-10, respectively. Conclusions This study demonstrates the practical feasibility of mPSDs. This type of detector could be very useful for pre-treatment quality assurance applications as well as an accurate tool for real-time in vivo dosimetry. PMID:23060069

Therriault-Proulx, Francois; Archambault, Louis; Beaulieu, Luc; Beddar, Sam

2013-01-01

119

Development of a novel multi-point plastic scintillation detector with a single optical transmission line for radiation dose measurement  

NASA Astrophysics Data System (ADS)

The goal of this study was to develop a novel multi-point plastic scintillation detector (mPSD) capable of measuring the dose accurately at multiple positions simultaneously using a single optical transmission line. A 2-point mPSD used a band-pass approach that included splitters, color filters and an EMCCD camera. The 3-point mPSD was based on a new full-spectrum approach, in which a spectrograph was coupled to a CCD camera. Irradiations of the mPSDs and of an ion chamber were performed with a 6 MV photon beam at various depths and lateral positions in a water tank. For the 2-point mPSD, the average relative differences between mPSD and ion chamber measurements for the depth-dose were 2.4±1.6% and 1.3±0.8% for BCF-60 and BCF-12, respectively. For the 3-point mPSD, the average relative differences over all conditions were 2.3±1.1%, 1.6±0.4% and 0.32±0.19% for BCF-60, BCF-12 and BCF-10, respectively. This study demonstrates the practical feasibility of mPSDs. This type of detector could be very useful for pre-treatment quality assurance applications as well as an accurate tool for real-time in vivo dosimetry. US Patent pending.

Therriault-Proulx, François; Archambault, Louis; Beaulieu, Luc; Beddar, Sam

2012-11-01

120

Development of a novel multi-point plastic scintillation detector with a single optical transmission line for radiation dose measurement.  

PubMed

The goal of this study was to develop a novel multi-point plastic scintillation detector (mPSD) capable of measuring the dose accurately at multiple positions simultaneously using a single optical transmission line. A 2-point mPSD used a band-pass approach that included splitters, color filters and an EMCCD camera. The 3-point mPSD was based on a new full-spectrum approach, in which a spectrograph was coupled to a CCD camera. Irradiations of the mPSDs and of an ion chamber were performed with a 6 MV photon beam at various depths and lateral positions in a water tank. For the 2-point mPSD, the average relative differences between mPSD and ion chamber measurements for the depth-dose were 2.4±1.6% and 1.3±0.8% for BCF-60 and BCF-12, respectively. For the 3-point mPSD, the average relative differences over all conditions were 2.3±1.1%, 1.6±0.4% and 0.32±0.19% for BCF-60, BCF-12 and BCF-10, respectively. This study demonstrates the practical feasibility of mPSDs. This type of detector could be very useful for pre-treatment quality assurance applications as well as an accurate tool for real-time in vivo dosimetry. PMID:23060069

Therriault-Proulx, François; Archambault, Louis; Beaulieu, Luc; Beddar, Sam

2012-11-01

121

Generating Arbitrary Chemical Patterns for Multi-Point Dosing of Single Cells  

PubMed Central

Living cells reside within anisotropic microenvironments that orchestrate a broad range of polarized responses through physical and chemical cues. To unravel how localized chemical signals influence complex behaviors, tools must be developed for establishing patterns of chemical gradients that vary over subcellular dimensions. Here, we present a strategy for addressing this critical need in which an arbitrary number of chemically distinct, subcellular dosing streams are created in real time within a microfluidic environment. In this approach, cells are cultured on a thin polymer membrane that serves as a barrier between the cell-culture environment and a reagent chamber containing multiple reagent species flowing in parallel under low Reynolds number conditions. Focal ablation of the membrane creates pores that allow solution to flow from desired regions within this reagent pattern into the cell-culture chamber, resulting in narrow, chemically distinct dosing streams. Unlike previous dosing strategies, this system provides the capacity to tailor arbitrary patterns of reagents on-the-fly to suit the geometry and orientation of specific cells. PMID:23427919

Hoppe, Todd J.; Moorjani, Samira G.; Shear, Jason B.

2013-01-01

122

Computational analysis of the maximum power point for GaAs sub-cells in InGaP/GaAs/Ge triple-junction space solar cells  

NASA Astrophysics Data System (ADS)

The radiation resistance in InGaP/GaAs/Ge triple-junction solar cells is limited by that of the middle GaAs sub-cell. In this work, the electrical performance degradation of different GaAs sub-cells under 1 MeV electron irradiation at fluences below 4 × 1015 cm−2 has been analyzed by means of a computer simulation. The numerical simulations have been carried out using the one-dimensional device modeling program PC1D. The effects of the base and emitter carrier concentrations of the p- and n-type GaAs structures on the maximum power point have been researched using a radiative recombination lifetime, a damage constant for the minority carrier lifetime and carrier removal rate models. An analytical model has been proposed, which is useful to either determine the maximum exposure time or select the appropriate device in order to ensure that the electrical parameters of different GaAs sub-cells will have a satisfactory response to radiation since they will be kept above 80% with respect to the non-irradiated values.

Cappelletti, M. A.; Cédola, A. P.; Blancá, E. L. Peltzer y.

2014-11-01

123

[Preservative substances - the daily dose of benzalkonium chloride in glaucoma treatment from the patients point of view].  

PubMed

The author calculated the daily dose of Benzalkonium Chloride (BAC) in eye drops used in glaucoma treatment from the patients point of view, which means the real amount of BAC applied in the conjunctival sac. The information about BAC concentration in 1 milliliter (mL) do not offer sufficient picture about real circumstances, because the size of the drop, especially after the introducing of the use of generic products in clinical practice in specific anti-glaucomatic drugs, differs significantly. The daily dose of BAC may have substantial significance in the patients treatment tolerance. The overview of BAC daily dose in single therapeutic groups and drugs follows: betablockers: Timo-COMOD 0, Arutimol 2.6, Vistagan 2.8, Timolol-POS 3.0, Arteoptic 3.7, Betoptic S 4.8, Timoptol MSD 6.3, Betoptic 10.0; alpha-mimetics: Alphagan 3.5, Luxfen 3.5, Aruclonin 7.1; derivates of prostaglandine, prostamides: Taflotan 0, Monopost 0, Lumigan 1.4, Unilat 3.1, Travatan 3.9, Latanoprost Apotex 4.3, Rescula 5.8, Latanoprost POS 5.9, Xalatan 6.0, Latanoprost Ratiopharm 6.0, Latanoprost Actavis 6.0, Latanoprost Arrow 6.0, Arulatan 5.4, Latalux 6.0, Glaucotens 6.0, Xaloptic 6.0, Solusin 6.1; carboanhydrase inhibitors: Batidor 3.8, Azopt 4.8, Trusopt 5.4, Oftidor 8.1; fixed combinations: Ganfort 1.4, Dorzolamid/timolol TEVA 2.8, Combigan 3.2, Duotrav 4.3, Cosopt 5.6, Xalacom 6.0, Glaucotima 6.0, Latanoprost/timolol Apotex 6.3, Azarga 6.4, Dorzogen Combi 6.5, and Dozotima 8.8 µl. Key words: glaucoma, antiglaucomatic treatment, preservatives, Benzalconium Chloride, BAC, daily dose of BAC. PMID:25032794

Výborný, P; Si?áková, S; Veselá Flórová, Z

2014-01-01

124

Use of lung toxicity and lung particle clearance to estimate the maximum tolerated dose (MTD) for a fiber glass chronic inhalation study in the rat.  

PubMed

Short-term toxicity and lung clearance were assessed in rats exposed by inhalation to size-selected fibrous glass (FG) for 13 weeks. Results from this study and from a recent FG chronic inhalation study are presented here as guidelines for the selection of a maximum tolerated dose (MTD) for chronic inhalation studies of fibers. Fischer 344 rats were exposed using nose-only inhalation chambers, 6 hr/day, 5 days/week, for 13 weeks to one of five concentrations of FG (36, 206, 316, 552, or 714 fibers/cc; expressed gravimetrically, 3, 16, 30, 45, or 60 mg/m3) or to filtered air. Rats were then held for an additional 10 weeks of postexposure recovery. Test fiber was size-selected from glass wool having a chemical composition representative of building insulation. Rats were terminated at 7, 13, 19, and 23 weeks after the onset of exposure to evaluate pulmonary pathology, lung epithelium cell proliferation, lung fiber burden, and lung lavage cells and chemistry. The effect of fiber inhalation on lung clearance of innocuous microspheres was also evaluated: following fiber exposure, six rats/group were exposed to 85Sr-labeled 3.0-microns polystyrene microspheres by intratracheal inhalation and then monitored for whole-body radioactivity during the 10-week recovery period. Data from the short-term study support the choice of 30 mg/m3 as the MTD for the previous chronic FG study and also provide indicators of long-term lung toxicity and functional impairment that can be used to estimate the MTD for future chronic fiber inhalation studies. PMID:8812213

Hesterberg, T W; McConnel, E E; Miiller, W C; Chevalier, J; Everitt, J; Thevenaz, P; Fleissner, H; Oberdörster, G

1996-07-01

125

Zero, minimum and maximum relative radial acceleration for planar formation flight dynamics near triangular libration points in the Earth-Moon system  

NASA Astrophysics Data System (ADS)

Assume a constellation of satellites is flying near a given nominal trajectory around L4 or L5 in the Earth-Moon system in such a way that there is some freedom in the selection of the geometry of the constellation. We are interested in avoiding large variations of the mutual distances between spacecraft. In this case, the existence of regions of zero and minimum relative radial acceleration with respect to the nominal trajectory will prevent from the expansion or contraction of the constellation. In the other case, the existence of regions of maximum relative radial acceleration with respect to the nominal trajectory will produce a larger expansion and contraction of the constellation. The goal of this paper is to study these regions in the scenario of the Circular Restricted Three Body Problem by means of a linearization of the equations of motion relative to the periodic orbits around L4 or L5. This study corresponds to a preliminar planar formation flight dynamics about triangular libration points in the Earth-Moon system. Additionally, the cost estimate to maintain the constellation in the regions of zero and minimum relative radial acceleration or keeping a rigid configuration is computed with the use of the residual acceleration concept. At the end, the results are compared with the dynamical behavior of the deviation of the constellation from a periodic orbit.

Salazar, F. J. T.; Masdemont, J. J.; Gómez, G.; Macau, E. E.; Winter, O. C.

2014-11-01

126

Dose point kernel for boron-11 decay and the cellular S values in boron neutron capture therapy  

SciTech Connect

The study of the radiobiology of boron neutron capture therapy is based on the cellular level dosimetry of boron-10's thermal neutron capture reaction {sup 10}B(n,{alpha}){sup 7}Li, in which one 1.47 MeV helium-4 ion and one 0.84 MeV lithium-7 ion are spawned. Because of the chemical preference of boron-10 carrier molecules, the dose is heterogeneously distributed in cells. In the present work, the (scaled) dose point kernel of boron-11 decay, called {sup 11}B-DPK, was calculated by GEANT4 Monte Carlo simulation code. The DPK curve drops suddenly at the radius of 4.26 {mu}m, the continuous slowing down approximation (CSDA) range of a lithium-7 ion. Then, after a slight ascending, the curve decreases to near zero when the radius goes beyond 8.20 {mu}m, which is the CSDA range of a 1.47 MeV helium-4 ion. With the DPK data, S values for nuclei and cells with the boron-10 on the cell surface are calculated for different combinations of cell and nucleus sizes. The S value for a cell radius of 10 {mu}m and a nucleus radius of 5 {mu}m is slightly larger than the value published by Tung et al. [Appl. Radiat. Isot. 61, 739-743 (2004)]. This result is potentially more accurate than the published value since it includes the contribution of a lithium-7 ion as well as the alpha particle.

Ma Yunzhi; Geng Jinpeng; Gao Song; Bao Shanglian [Research Center for Tumor Diagnosis and Radiotherapy Physics and Laboratory of Medical Physics and Engineering, Peking University, Beijing 100871 (China); Department of Nuclear Physics, Chinese Institute of Atomic Energy, Beijing, 102413 (China); Research Center for Tumor Diagnosis and Radiotherapy Physics and Laboratory of Medical Physics and Engineering, Peking University, Beijing 100871 (China)

2006-12-15

127

Why are there no really big bony fishes? A point-of-view on maximum body size in teleosts and elasmobranchs  

Microsoft Academic Search

The most massive teleost, the ocean sunfish(Mola mola), is an order of magnitude smaller than the largest cartilaginous fish,the whale shark (Rhincodon typus), and issignificantly smaller than several other extantelasmobranch species. Possible reasons for this discrepancy in maximum size include:anatomical, physiological, ecological, and life-history\\/ontogenetic constraints. Weexamined life-history traits and growth ratesas the most likely constraints on maximum teleostsize. For pelagic

Jonathan A. Freedman; David L. G. Noakes

2002-01-01

128

Calculation of absorbed dose and biological effectiveness from photonuclear reactions in a bremsstrahlung beam of end point 50 MeV  

Microsoft Academic Search

The absorbed dose due to photonuclear reactions in soft tissue, lung, breast, adipose tissue and cortical bone has been evaluated for a scanned bremsstrahlung beam of end point 50 MeV from a racetrack accelerator. The Monte Carlo code MCNP4B was used to determine the photon source spectrum from the bremsstrahlung target and to simulate the transport of photons through the

I. Gudowska; A. Brahme; P. Andreo; W. Gudowski; J. Kierkegaard

1999-01-01

129

Pharmacokinetic/Pharmacodynamic modeling of abexinostat-induced thrombocytopenia across different patient populations: application for the determination of the maximum tolerated doses in both lymphoma and solid tumour patients.  

PubMed

Background In the clinical development of oncology drugs, the recommended dose is usually determined using a 3?+?3 dose-escalation study design. However, this phase I design does not always adequately describe dose-toxicity relationships. Methods 125 patients, with either solid tumours or lymphoma, were included in the study and 1217 platelet counts were available over three treatment cycles. The data was used to build a population pharmacokinetic/pharmacodynamic (PKPD) model using a sequential modeling approach. Model-derived Recommended Doses (MDRD) of abexinostat (a Histone Deacetylase Inhibitor) were determined from simulations of different administration schedules, and the higher bound for the probability of reaching these MDRD with a 3?+?3 design were obtained. Results The PKPD model developed adequately described platelet kinetics in both patient populations with the inclusion of two platelet baseline counts and a disease progression component for patients with lymphoma. Simulation results demonstrated that abexinostat administration during the first 4 days of each week in a 3-week cycle led to a higher MDRD compared to the other administration schedules tested, with a maximum probability of 40 % of reaching these MDRDs using a 3?+?3 design. Conclusions The PKPD model was able to predict thrombocytopenia following abexinostat administration in both patient populations. A model-based approach to determine the recommended dose in phase I trials is preferable due to the imprecision of the 3?+?3 design. PMID:24875134

Chalret du Rieu, Quentin; Fouliard, Sylvain; White-Koning, Mélanie; Kloos, Ioana; Chatelut, Etienne; Chenel, Marylore

2014-10-01

130

Dose point kernels in liquid water: an intra-comparison between GEANT4-DNA and a variety of Monte Carlo codes.  

PubMed

Modeling the radio-induced effects in biological medium still requires accurate physics models to describe the interactions induced by all the charged particles present in the irradiated medium in detail. These interactions include inelastic as well as elastic processes. To check the accuracy of the very low energy models recently implemented into the GEANT4 toolkit for modeling the electron slowing-down in liquid water, the simulation of electron dose point kernels remains the preferential test. In this context, we here report normalized radial dose profiles, for mono-energetic point sources, computed in liquid water by using the very low energy "GEANT4-DNA" physics processes available in the GEANT4 toolkit. In the present study, we report an extensive intra-comparison of profiles obtained by a large selection of existing and well-documented Monte-Carlo codes, namely, EGSnrc, PENELOPE, CPA100, FLUKA and MCNPX. PMID:23478094

Champion, C; Incerti, S; Perrot, Y; Delorme, R; Bordage, M C; Bardiès, M; Mascialino, B; Tran, H N; Ivanchenko, V; Bernal, M; Francis, Z; Groetz, J-E; Fromm, M; Campos, L

2014-01-01

131

Are bigger data sets better for machine learning? Fusing single-point and dual-event dose response data for Mycobacterium tuberculosis.  

PubMed

Tuberculosis is a major, neglected disease for which the quest to find new treatments continues. There is an abundance of data from large phenotypic screens in the public domain against Mycobacterium tuberculosis (Mtb). Since machine learning methods can learn from past data, we were interested in addressing whether more data builds better models. We now describe using Bayesian machine learning to assess whether we can improve our models by combining the large quantities of single-point data with the much smaller (higher quality) dual-event data sets, which use both dose-response data for both whole-cell antitubercular activity and Vero cell cytotoxicity. We have evaluated 12 models ranging from different single-point, dual-event dose-response, single-point and dual-event dose-response as well as combined data sets for three distinct data sets from the same laboratory. We used a fourth data set of active and inactive compounds from the same group as well as a smaller set of 177 active compounds from GlaxoSmithKline as test sets. Our data suggest combining single-point with dual-event dose-response data does not diminish the internal or external predictive ability of the models based on the receiver operator curve (ROC) for these models (internal ROC range 0.83-0.91, external ROC range 0.62-0.83) compared to the orders of magnitude smaller dual-event models (internal ROC range 0.6-0.83 and external ROC 0.54-0.83). In conclusion, models developed with 1200-5000 compounds appear to be as predictive as those generated with 25?000-350?000 molecules. Our results have implications for justifying further high-throughput screening versus focused testing based on model predictions. PMID:24968215

Ekins, Sean; Freundlich, Joel S; Reynolds, Robert C

2014-07-28

132

Calculation of electron and isotopes dose point kernels with fluka Monte Carlo code for dosimetry in nuclear medicine therapy  

Microsoft Academic Search

The calculation of patient-specific dose distribution can be achieved by Monte Carlo simulations or by analytical methods. In this study, fluka Monte Carlo code has been considered for use in nuclear medicine dosimetry. Up to now, fluka has mainly been dedicated to other fields, namely high energy physics, radiation protection, and hadrontherapy. When first employing a Monte Carlo code for

F. Botta; M. Cremonesi; A. Di Dia; G. Pedroli; A. Mairani; G. Battistoni; A. Fassò; A. Ferrari; M. Ferrari; G. Paganelli; M. Valente

2011-01-01

133

Evaluation of Rectal Dose During High-Dose-Rate Intracavitary Brachytherapy for Cervical Carcinoma  

SciTech Connect

High-dose-rate intracavitary brachytherapy (HDR-ICBT) for carcinoma of the uterine cervix often results in high doses being delivered to surrounding organs at risk (OARs) such as the rectum and bladder. Therefore, it is important to accurately determine and closely monitor the dose delivered to these OARs. In this study, we measured the dose delivered to the rectum by intracavitary applications and compared this measured dose to the International Commission on Radiation Units and Measurements rectal reference point dose calculated by the treatment planning system (TPS). To measure the dose, we inserted a miniature (0.1 cm{sup 3}) ionization chamber into the rectum of 86 patients undergoing radiation therapy for cervical carcinoma. The response of the miniature chamber modified by 3 thin lead marker rings for identification purposes during imaging was also characterized. The difference between the TPS-calculated maximum dose and the measured dose was <5% in 52 patients, 5-10% in 26 patients, and 10-14% in 8 patients. The TPS-calculated maximum dose was typically higher than the measured dose. Our study indicates that it is possible to measure the rectal dose for cervical carcinoma patients undergoing HDR-ICBT. We also conclude that the dose delivered to the rectum can be reasonably predicted by the TPS-calculated dose.

Sha, Rajib Lochan [Department of Radiation Physics, Indo-American Cancer Institute and Research Centre, Hyderabad (India); Department of Physics, Osmania University, Hyderabad (India); Reddy, Palreddy Yadagiri [Department of Physics, Osmania University, Hyderabad (India); Rao, Ramakrishna [Department of Radiation Physics, MNJ Institute of Oncology and Regional Cancer Center, Hyderabad (India); Muralidhar, Kanaparthy R. [Department of Radiation Physics, Indo-American Cancer Institute and Research Centre, Hyderabad (India); Kudchadker, Rajat J., E-mail: rkudchad@mdanderson.org [Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, TX (United States)

2011-01-01

134

A dose point kernel database using GATE Monte Carlo simulation toolkit for nuclear medicine applications: Comparison with other Monte Carlo codes  

SciTech Connect

Purpose: GATE is a Monte Carlo simulation toolkit based on the Geant4 package, widely used for many medical physics applications, including SPECT and PET image simulation and more recently CT image simulation and patient dosimetry. The purpose of the current study was to calculate dose point kernels (DPKs) using GATE, compare them against reference data, and finally produce a complete dataset of the total DPKs for the most commonly used radionuclides in nuclear medicine. Methods: Patient-specific absorbed dose calculations can be carried out using Monte Carlo simulations. The latest version of GATE extends its applications to Radiotherapy and Dosimetry. Comparison of the proposed method for the generation of DPKs was performed for (a) monoenergetic electron sources, with energies ranging from 10 keV to 10 MeV, (b) beta emitting isotopes, e.g., {sup 177}Lu, {sup 90}Y, and {sup 32}P, and (c) gamma emitting isotopes, e.g., {sup 111}In, {sup 131}I, {sup 125}I, and {sup 99m}Tc. Point isotropic sources were simulated at the center of a sphere phantom, and the absorbed dose was stored in concentric spherical shells around the source. Evaluation was performed with already published studies for different Monte Carlo codes namely MCNP, EGS, FLUKA, ETRAN, GEPTS, and PENELOPE. A complete dataset of total DPKs was generated for water (equivalent to soft tissue), bone, and lung. This dataset takes into account all the major components of radiation interactions for the selected isotopes, including the absorbed dose from emitted electrons, photons, and all secondary particles generated from the electromagnetic interactions. Results: GATE comparison provided reliable results in all cases (monoenergetic electrons, beta emitting isotopes, and photon emitting isotopes). The observed differences between GATE and other codes are less than 10% and comparable to the discrepancies observed among other packages. The produced DPKs are in very good agreement with the already published data, which allowed us to produce a unique DPKs dataset using GATE. The dataset contains the total DPKs for {sup 67}Ga, {sup 68}Ga, {sup 90}Y, {sup 99m}Tc, {sup 111}In, {sup 123}I, {sup 124}I, {sup 125}I, {sup 131}I, {sup 153}Sm, {sup 177}Lu {sup 186}Re, and {sup 188}Re generated in water, bone, and lung. Conclusions: In this study, the authors have checked GATE's reliability for absorbed dose calculation when transporting different kind of particles, which indicates its robustness for dosimetry applications. A novel dataset of DPKs is provided, which can be applied in patient-specific dosimetry using analytical point kernel convolution algorithms.

Papadimitroulas, Panagiotis; Loudos, George; Nikiforidis, George C.; Kagadis, George C. [Department of Medical Physics, School of Medicine, University of Patras, Rion, GR 265 04 (Greece) and Department of Medical Instruments Technology, Technological Educational institute of Athens, Ag. Spyridonos Street, Egaleo GR 122 10, Athens (Greece); Department of Medical Instruments Technology, Technological Educational institute of Athens, Ag. Spyridonos Street, Egaleo GR 122 10, Athens (Greece); Department of Medical Physics, School of Medicine, University of Patras, Rion, GR 265 04 (Greece)

2012-08-15

135

Maximum Likelihood  

NSDL National Science Digital Library

This material introduces the basic theory of maximum likelihood estimation by discussing the likelihood function, the log likelihood function, and maximizing these functions using calculus. Several exercises ask students to derive certain estimators, while others have students compare the behavior of those estimators with other possibilities through the use of various JAVA applets. The applets use the same control features: the sliders set the parameter values, the ÃÂStop #ÃÂ drop down menu sets the number of samples taken, the ÃÂUpdate #ÃÂ drop down menu sets how often the graph and tables update during the experiment, the single arrow takes one sample, the double arrow runs the full experiment, the square stops the experiment, and the back arrow resets the applet. This page is one lesson from the Virtual Laboratories in Statistics.

Siegrist, Kyle

2009-07-20

136

Comparative evaluation of US Food and Drug Administration and pharmacologically guided approaches to determine the maximum recommended starting dose for first-in-human clinical trials in adult healthy men.  

PubMed

The authors compared US Food and Drug Administration (FDA) and 9 pharmacologically guided approaches (PGAs; simple allometry, maximum life span potential [MLP], brain weight, rule of exponent [ROE], two 2-sp methods and 3 one-sp methods) to determine the maximum recommended starting dose (MRSD) for first-in-human clinical trials in adult healthy men using 10 drugs. The ROE method as suggested by Mahmood and Balian1 gave the best prediction accuracy for a pharmacokinetic (PK) parameter. Values derived from clearance were consistently better than volume of distribution (Vd)-based methods and had lower root mean square error (RMSE) values. A pictorial method evaluation chart was developed based on fold errors for simultaneous evaluation of various methods. The one-sp method (rat) and the US FDA methods gave the highest prediction accuracy and low RMSE values, and the 2-sp methods gave the least prediction accuracy with high RMSE values. The ROE method gave more consistent predictions for PK parameters than other allometric methods. Despite this, the MRSD predictions were not better than US FDA methods, probably indicating that across-species variation in clearance may be higher than variation in no observed adverse effect level (NOAEL) and that PGA methods may not be consistently better than the NOAEL based methods. PMID:21415286

Imam, Md Tarique; Venkateshan, S P; Tandon, Monika; Saha, Nilanjan; Pillai, K K

2011-12-01

137

Effect of oxygen dosing point and mixing on the microaerobic removal of hydrogen sulphide in sludge digesters.  

PubMed

Limited oxygen supply to anaerobic sludge digesters to remove hydrogen sulphide from biogas was studied. Micro-oxygenation showed competitive performance to reduce considerably the additional equipment necessary to perform biogas desulphurization. Two pilot-plant digesters with an HRT of ? 20 d were micro-oxygenated at a rate of 0.25 NL per L of feed sludge with a removal efficiency higher than 98%. The way of mixing (sludge or biogas recirculation) and the point of oxygen supply (headspace or liquid phase) played an important role on hydrogen sulphide oxidation. While micro-oxygenation with sludge recirculation removed only hydrogen sulphide from the biogas, dissolved sulphide was removed if micro-oxygenation was performed with biogas recirculation. Dosage in the headspace resulted in a more stable operation. The result of the hydrogen sulphide oxidation was mostly elemental sulphur, partially accumulated in the headspace of the digester, where different sulphide-oxidising bacteria were found. PMID:21193305

Díaz, I; Pérez, S I; Ferrero, E M; Fdz-Polanco, M

2011-02-01

138

New insights on P-related paramagnetic point defects in irradiated phosphate glasses: Impact of glass network type and irradiation dose  

NASA Astrophysics Data System (ADS)

P-related paramagnetic point defects were studied in irradiated Yb-doped phosphate glasses by electron paramagnetic resonance spectroscopy (X and Q-bands). A strong impact of the glass network type on the defect nature is shown. In all glasses, r-POHC defects formation is in strong correlation with Q2 tetrahedra amount supporting the structure of r-POHC. Ultra-phosphate glasses contain the larger defect type: Peroxy radicals, P1, P2, and P4 defects whose formation is linked to Q3 tetrahedra presence. In meta-phosphate and poly-phosphate glasses, peroxy radicals appear with r-POHC thermal recovery. In meta-phosphate glasses, a combination of P1 and P3 defects was evidenced for the first time, whereas in poly-phosphate glasses, only P3 defects were identified. Dose effect as well as defect recovery were analyzed.

Pukhkaya, V.; Trompier, F.; Ollier, N.

2014-09-01

139

Cord Dose Specification and Validation for Stereotactic Body Radiosurgery of Spine  

SciTech Connect

Effective dose to a portion of the spinal cord in treatment segment, rather than the maximum point dose in the cord surface, was set as the dose limit in stereotactic-body radiosurgery (SBRS) of spine. Such a cord dose specification is sensitive to the volume size and position errors. Thus, we used stereotactic image guidance to minimize phantom positioning errors and compared the results of a 0.6-cm{sup 3} Farmer ionization chamber and a 0.01-cm{sup 3} compact ionization chamber to determine the detector size effect on 9 SBRS cases. The experimental errors ranging from 2% to 7% were estimated by the deviation of the mean dose in plans to the chamber with spatial displacements of 0.5 mm. The mean and measured doses for the large chamber to individual cases were significantly ({approx}17%) higher than the doses with the compact chamber placed at the same point. Our experimental results shown that the mean doses to the volume of interest could represent the measured cord doses. For the 9 patients, the mean doses to 10% of the cord were about 10 Gy, while the maximum cord doses varied from 11.6 to 17.6 Gy. The mean dose, possibly correlated with the cord complication, provided us an alternative and reliable cord dose specification in SBRS of spine.

Li Shidong [Department of Radiation Oncology, Henry Ford Health System, Detroit, MI (United States) and Department of Radiation Oncology, Temple University Hospital, Philadelphia, PA (United States)], E-mail: Shidong.Li@thus.temple.edu; Liu Yan; Chen Qing; Jin Jianyue [Department of Radiation Oncology, Henry Ford Health System, Detroit, MI (United States) Department of Radiation Oncology, Temple University Hospital, Philadelphia, PA (United States)

2009-01-01

140

Variability of Marker-Based Rectal Dose Evaluation in HDR Cervical Brachytherapy  

SciTech Connect

In film-based intracavitary brachytherapy for cervical cancer, position of the rectal markers may not accurately represent the anterior rectal wall. This study was aimed at analyzing the variability of rectal dose estimation as a result of interfractional variation of marker placement. A cohort of five patients treated with multiple-fraction tandem and ovoid high-dose-rate (HDR) brachytherapy was studied. The cervical os point and the orientation of the applicators were matched among all fractional plans for each patient. Rectal points obtained from all fractions were then input into each clinical treated plan. New fractional rectal doses were obtained and a new cumulative rectal dose for each patient was calculated. The maximum interfractional variation of distances between rectal dose points and the closest source positions was 1.1 cm. The corresponding maximum variability of fractional rectal dose was 65.5%. The percentage difference in cumulative rectal dose estimation for each patient was 5.4%, 19.6%, 34.6%, 23.4%, and 13.9%, respectively. In conclusion, care should be taken when using rectal markers as reference points for estimating rectal dose in HDR cervical brachytherapy. The best estimate of true rectal dose for each fraction should be determined by the most anterior point among all fractions.

Wang Zhou, E-mail: Zhou.Wang@RoswellPark.or [Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY (United States); Jaggernauth, Wainwright; Malhotra, Harish K.; Podgorsak, Matthew B. [Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY (United States)

2010-01-01

141

Generalized Maximum Entropy  

NASA Technical Reports Server (NTRS)

A long standing mystery in using Maximum Entropy (MaxEnt) is how to deal with constraints whose values are uncertain. This situation arises when constraint values are estimated from data, because of finite sample sizes. One approach to this problem, advocated by E.T. Jaynes [1], is to ignore this uncertainty, and treat the empirically observed values as exact. We refer to this as the classic MaxEnt approach. Classic MaxEnt gives point probabilities (subject to the given constraints), rather than probability densities. We develop an alternative approach that assumes that the uncertain constraint values are represented by a probability density {e.g: a Gaussian), and this uncertainty yields a MaxEnt posterior probability density. That is, the classic MaxEnt point probabilities are regarded as a multidimensional function of the given constraint values, and uncertainty on these values is transmitted through the MaxEnt function to give uncertainty over the MaXEnt probabilities. We illustrate this approach by explicitly calculating the generalized MaxEnt density for a simple but common case, then show how this can be extended numerically to the general case. This paper expands the generalized MaxEnt concept introduced in a previous paper [3].

Cheeseman, Peter; Stutz, John

2005-01-01

142

Special State Standard of absorbed dose unit of x-ray radiation with maximum photon energy from 3 to 9 fJ (20–60 keV)  

Microsoft Academic Search

The special State standard reproduces the absorbed dose unit of x-ray radiation in an absorber within the range from 1 to 5 J\\/kg. The unit is reproduced by calorimetric techniques which is the only method of direct and absolute measurement of absorbed radiation energy. In compliance with the ICRU recommendations, the absorber material is graphite. The block diagram of the

R. F. Kononova; A. P. Sebekin; V. I. Fominykh; M. F. Yudin

1976-01-01

143

SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: Measurement of radiation dose at the north interaction point of BEPC II  

NASA Astrophysics Data System (ADS)

The technique details for measuring radiation dose are expounded. The results of gamma and neutron radiation levels are presented and the corresponding radiation shielding is discussed based on the simplified estimation. In addition, the photon radiation level move as background for future experiments is measured by a NaI(Tl) detector.

Mo, Xiao-Hu; Zhang, Jian-Yong; Zhang, Tian-Bao; Zhang, Qing-Jiang; Achasov, Mikhail; Fu, Cheng-Dong; Muchnoi, Nikolay; Qin, Qing; Qu, Hua-Min; Wang, Yi-Fang; Wu, Jing-Min; Xu, Jin-Qiang; Yu, Bo-Xiang

2009-10-01

144

Next generation of adeno-associated virus 2 vectors: Point mutations in tyrosines lead to high-efficiency transduction at lower doses  

PubMed Central

Recombinant adeno-associated virus 2 (AAV2) vectors are in use in several Phase I/II clinical trials, but relatively large vector doses are needed to achieve therapeutic benefits. Large vector doses also trigger an immune response as a significant fraction of the vectors fails to traffic efficiently to the nucleus and is targeted for degradation by the host cell proteasome machinery. We have reported that epidermal growth factor receptor protein tyrosine kinase (EGFR-PTK) signaling negatively affects transduction by AAV2 vectors by impairing nuclear transport of the vectors. We have also observed that EGFR-PTK can phosphorylate AAV2 capsids at tyrosine residues. Tyrosine-phosphorylated AAV2 vectors enter cells efficiently but fail to transduce effectively, in part because of ubiquitination of AAV capsids followed by proteasome-mediated degradation. We reasoned that mutations of the surface-exposed tyrosine residues might allow the vectors to evade phosphorylation and subsequent ubiquitination and, thus, prevent proteasome-mediated degradation. Here, we document that site-directed mutagenesis of surface-exposed tyrosine residues leads to production of vectors that transduce HeLa cells ?10-fold more efficiently in vitro and murine hepatocytes nearly 30-fold more efficiently in vivo at a log lower vector dose. Therapeutic levels of human Factor IX (F.IX) are also produced at an ?10-fold reduced vector dose. The increased transduction efficiency of tyrosine-mutant vectors is due to lack of capsid ubiquitination and improved intracellular trafficking to the nucleus. These studies have led to the development of AAV vectors that are capable of high-efficiency transduction at lower doses, which has important implications in their use in human gene therapy. PMID:18511559

Zhong, Li; Li, Baozheng; Mah, Cathryn S.; Govindasamy, Lakshmanan; Agbandje-McKenna, Mavis; Cooper, Mario; Herzog, Roland W.; Zolotukhin, Irene; Warrington, Kenneth H.; Weigel-Van Aken, Kirsten A.; Hobbs, Jacqueline A.; Zolotukhin, Sergei; Muzyczka, Nicholas; Srivastava, Arun

2008-01-01

145

Conversion of dose-volume constraints to dose limits.  

PubMed

The purpose of this study is to introduce two techniques for converting dose-volume constraints to dose limits for treatment planning optimization, and to evaluate their performance. The first technique, called dose-sorting, is based on the assumption that higher dose limits should be assigned to the constraint points receiving higher doses, and vice versa. The second technique, the hybrid technique, is a hybrid of the dose-sorting technique and the mixed integer linear programming (MILP) technique. Among all constraint points in an organ at risk, the dose limits for the points far from a dose-volume constraint are determined by dose-sorting, while the dose limits for the points close to a dose-volume constraint are determined by MILP. We evaluated the performance of the two new techniques for one treatment geometry by comparing them with the MILP technique. The dose-sorting technique had a high probability of finding the global optimum when no more than three organs at risk have dose-volume constraints. It was much faster than the MILP technique. The hybrid technique always found the global optimum when the MILP percentage (the percentage of constraint points for which the dose limits are determined by the MILP technique) was large enough, but its computation time increased dramatically with the MILP percentage. In conclusion, the dose-sorting technique and the hybrid technique with a low MILP percentage are clinically feasible. PMID:14703167

Dai, Jianrong; Zhu, Yunping

2003-12-01

146

The maximum modulus of a trigonometric trinomial  

Microsoft Academic Search

Let ? be a set of three integers and let \\u000a be the space of 2?-periodic functions with spectrum in ? endowed with the maximum modulus norm. We isolate the maximum modulus points x of trigonometric trinomials T ? \\u000a and prove that x is unique unless |T| has an axis of symmetry. This enables us to compute the exposed and the

Stefan Neuwirth

2008-01-01

147

Direct measurement of a patient's entrance skin dose during pediatric cardiac catheterization.  

PubMed

Children with complex congenital heart diseases often require repeated cardiac catheterization; however, children are more radiosensitive than adults. Therefore, radiation-induced carcinogenesis is an important consideration for children who undergo those procedures. We measured entrance skin doses (ESDs) using radio-photoluminescence dosimeter (RPLD) chips during cardiac catheterization for 15 pediatric patients (median age, 1.92 years; males, n = 9; females, n = 6) with cardiac diseases. Four RPLD chips were placed on the patient's posterior and right side of the chest. Correlations between maximum ESD and dose-area products (DAP), total number of frames, total fluoroscopic time, number of cine runs, cumulative dose at the interventional reference point (IRP), body weight, chest thickness, and height were analyzed. The maximum ESD was 80 ± 59 (mean ± standard deviation) mGy. Maximum ESD closely correlated with both DAP (r = 0.78) and cumulative dose at the IRP (r = 0.82). Maximum ESD for coiling and ballooning tended to be higher than that for ablation, balloon atrial septostomy, and diagnostic procedures. In conclusion, we directly measured ESD using RPLD chips and found that maximum ESD could be estimated in real-time using angiographic parameters, such as DAP and cumulative dose at the IRP. Children requiring repeated catheterizations would be exposed to high radiation levels throughout their lives, although treatment influences radiation dose. Therefore, the radiation dose associated with individual cardiac catheterizations should be analyzed, and the effects of radiation throughout the lives of such patients should be followed. PMID:24968708

Sun, Lue; Mizuno, Yusuke; Iwamoto, Mari; Goto, Takahisa; Koguchi, Yasuhiro; Miyamoto, Yuka; Tsuboi, Koji; Chida, Koichi; Moritake, Takashi

2014-11-01

148

Direct measurement of a patient's entrance skin dose during pediatric cardiac catheterization  

PubMed Central

Children with complex congenital heart diseases often require repeated cardiac catheterization; however, children are more radiosensitive than adults. Therefore, radiation-induced carcinogenesis is an important consideration for children who undergo those procedures. We measured entrance skin doses (ESDs) using radio-photoluminescence dosimeter (RPLD) chips during cardiac catheterization for 15 pediatric patients (median age, 1.92 years; males, n = 9; females, n = 6) with cardiac diseases. Four RPLD chips were placed on the patient's posterior and right side of the chest. Correlations between maximum ESD and dose–area products (DAP), total number of frames, total fluoroscopic time, number of cine runs, cumulative dose at the interventional reference point (IRP), body weight, chest thickness, and height were analyzed. The maximum ESD was 80 ± 59 (mean ± standard deviation) mGy. Maximum ESD closely correlated with both DAP (r = 0.78) and cumulative dose at the IRP (r = 0.82). Maximum ESD for coiling and ballooning tended to be higher than that for ablation, balloon atrial septostomy, and diagnostic procedures. In conclusion, we directly measured ESD using RPLD chips and found that maximum ESD could be estimated in real-time using angiographic parameters, such as DAP and cumulative dose at the IRP. Children requiring repeated catheterizations would be exposed to high radiation levels throughout their lives, although treatment influences radiation dose. Therefore, the radiation dose associated with individual cardiac catheterizations should be analyzed, and the effects of radiation throughout the lives of such patients should be followed. PMID:24968708

Sun, Lue; Mizuno, Yusuke; Iwamoto, Mari; Goto, Takahisa; Koguchi, Yasuhiro; Miyamoto, Yuka; Tsuboi, Koji; Chida, Koichi; Moritake, Takashi

2014-01-01

149

Determination of absorbed dose in water at the reference point D(r{sub 0},{theta}{sub 0}) for an {sup 192}Ir HDR brachytherapy source using a Fricke system  

SciTech Connect

A ring-shaped Fricke device was developed to measure the absolute dose on the transverse bisector of a {sup 192}Ir high dose rate (HDR) source at 1 cm from its center in water, D(r{sub 0},{theta}{sub 0}). It consists of a polymethylmethacrylate (PMMA) rod (axial axis) with a cylindrical cavity at its center to insert the {sup 192}Ir radioactive source. A ring cavity around the source with 1.5 mm thickness and 5 mm height is centered at 1 cm from the central axis of the source. This ring cavity is etched in a disk shaped base with 2.65 cm diameter and 0.90 cm thickness. The cavity has a wall around it 0.25 cm thick. This ring is filled with Fricke solution, sealed, and the whole assembly is immersed in water during irradiations. The device takes advantage of the cylindrical geometry to measure D(r{sub 0},{theta}{sub 0}). Irradiations were performed with a Nucletron microselectron HDR unit loaded with an {sup 192}Ir Alpha Omega radioactive source. A Spectronic 1001 spectrophotometer was used to measure the optical absorbance using a 1 mL quartz cuvette with 1.00 cm light pathlength. The PENELOPE Monte Carlo code (MC) was utilized to simulate the Fricke device and the {sup 192}Ir Alpha Omega source in detail to calculate the perturbation introduced by the PMMA material. A NIST traceable calibrated well type ionization chamber was used to determine the air-kerma strength, and a published dose-rate constant was used to determine the dose rate at the reference point. The time to deliver 30.00 Gy to the reference point was calculated. This absorbed dose was then compared to the absorbed dose measured by the Fricke solution. Based on MC simulation, the PMMA of the Fricke device increases the D(r{sub 0},{theta}{sub 0}) by 2.0%. Applying the corresponding correction factor, the D(r{sub 0},{theta}{sub 0}) value assessed with the Fricke device agrees within 2.0% with the expected value with a total combined uncertainty of 3.43%(k=1). The Fricke device provides a promising method towards calibration of brachytherapy radiation sources in terms of D(r{sub 0},{theta}{sub 0}) and audit HDR source calibrations.

Austerlitz, C.; Mota, H. C.; Sempau, J.; Benhabib, S. M.; Campos, D.; Allison, R.; Almeida, C. E. de; Zhu, D.; Sibata, C. H. [Department of Radiation Oncology, East Carolina University, Greenville, North Carolina 27834 (United States); Institut de Tecniques Energetiques, Universitat Politecnica de Catalunya, 08028 Barcelona (Spain); Department of Radiation Oncology, East Carolina University, Greenville, North Carolina 27834 (United States); Laboratorio de Cie circumflex ncias Radiologicas, Universidade do Estado do Rio de Janeiro, 20550 Rio de Janeiro (Brazil); Department of Radiation Oncology, East Carolina University, Greenville, North Carolina 27834 (United States)

2008-12-15

150

Last Glacial Maximum  

NSDL National Science Digital Library

Short lecture on CLIMAP project (see PowerPoint) 20 minutes Powerpoint (PowerPoint 444kB Nov7 10) Group activity - Reading for CLIMAP study assumptions, 20 minutes to read, 20 minutes for discussion Student Handout (Microsoft Word 50kB Nov7 10) Students break into groups (4 per group is good division of work) with 2 students per paper. Split the assumptions between students. Each group skims the CLIMAP papers for the assumptions (modern and/or LGM) used in the CLIMAP model-based reconstruction of the LGM. In the groups, students compare the assumptions between papers. Resources: CLIMAP (1976), The surface of the ice-age earth, Science, 191(4232), 1131-1137 and CLIMAP (1984), The last interglacial ocean, Quaternary Research, 21(2), 123. Class Discussion - Summarize assumptions used in CLIMAP studies. Group activity Exploring CLIMAP LGM Reconstructions, 40 minutes for model data, 20 minutes for discussion (Could be modified with as a "jigsaw" activity with a larger class). Learn more about the jigsaw teaching method. Students work on this activity in pairs; one person will create LGM maps, the other modern. Students should sit together with their computer monitors close together to compare. The students will use the IRI/LDEO Climate Data Library to access the CLIMAP reconstruction and produce maps using the tools available on this web site. In a web browser, go to http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/ This is the main page for the CLIMAP Model output for the LGM 18,000 BP. In the middle of the page is the label "Datasets and variables" with two data sets below http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/.LGM/ and http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/.MOD/. Each student clicks on the link they are assigned to. There are several data sets listed for each period and the students will examine each data set and compare the LGM and Modern. As a class, go through each data set allowing pairs to compare the maps then summarize the results as a class. The worksheet has a table for the students and the PowerPoint has table for summarizing. Class Discussion - Summarize differences between modern and LGM in the CLIMAP model output. Discuss how the assumptions of the CLIMAP model studies may have influenced the results. Extra activities The students can explore the data further using the data selection and filters in the IRI/LDEO Climate Data Library. For the two SST data sets, click on "Data Selection" and narrow the data to the just the tropics (23.5º N-S). Click on "Filters" then select XY next to "Average over." The next window gives you the average over the tropics close to the top of the page. In the next class, the students repeat the Readings exercise by reading the COHMAP and MARGO papers to see how the scientific knowledge has progressed since the original CLIMAP studies. COHMAP Members, (1988), Climatic Changes of the Last 18,000 Years: Observations and Model Simulations, Science, 241(4869), 1043-1052. MARGO (2009), Constraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum, Nature Geoscience, 2(2), 127-132.

Delong, Kristine

151

Stellar disks Maximum disk  

E-print Network

& Stellar Systems 5, ch.21 (1965) 7 P.C. van der Kruit & K.C. Freeman, K.C., Ap.J. 303, 556 (1986) Piet vanOutline Stellar disks Maximum disk Truncations Conclusions STRUCTURE, MASS AND STABILITY Stellar disks Maximum disk Truncations Conclusions Outline Stellar disks Vertical stellar dynamics Stellar

Kruit, Piet van der

152

Maximum thrust mode evaluation  

NASA Technical Reports Server (NTRS)

Measured reductions in acceleration times which resulted from the application of the F-15 performance seeking control (PSC) maximum thrust mode during the dual-engine test phase is presented as a function of power setting and flight condition. Data were collected at altitudes of 30,000 and 45,000 feet at military and maximum afterburning power settings. The time savings for the supersonic acceleration is less than at subsonic Mach numbers because of the increased modeling and control complexity. In addition, the propulsion system was designed to be optimized at the mid supersonic Mach number range. Recall that even though the engine is at maximum afterburner, PSC does not trim the afterburner for the maximum thrust mode. Subsonically at military power, time to accelerate from Mach 0.6 to 0.95 was cut by between 6 and 8 percent with a single engine application of PSC, and over 14 percent when both engines were optimized. At maximum afterburner, the level of thrust increases were similar in magnitude to the military power results, but because of higher thrust levels at maximum afterburner and higher aircraft drag at supersonic Mach numbers the percentage thrust increase and time to accelerate was less than for the supersonic accelerations. Savings in time to accelerate supersonically at maximum afterburner ranged from 4 to 7 percent. In general, the maximum thrust mode has performed well, demonstrating significant thrust increases at military and maximum afterburner power. Increases of up to 15 percent at typical combat-type flight conditions were identified. Thrust increases of this magnitude could be useful in a combat situation.

Orme, John S.; Nobbs, Steven G.

1995-01-01

153

Maximum ratio transmission  

Microsoft Academic Search

This paper presents the concept, principles, and analysis of maximum ratio transmission for wireless communications, where multiple antennas are used for both transmission and reception. The principles and analysis are applicable to general cases, including maximum-ratio combining. Simulation results agree with the analysis. The analysis shows that the average overall signal-to-mise ratio (SNR) is proportional to the cross correlation between

Titus K. Y. Lo

1999-01-01

154

Maximum Parsimony and Maximum Likelihood Methods Comparisons and Bootstrap Tests  

E-print Network

Maximum Parsimony and Maximum Likelihood Methods Comparisons and Bootstrap Tests Character Likelihood Methods Comparisons and Bootstrap Tests Character Reconstruction PHYLIP and T-REX Exercises Outline 1 Maximum Parsimony and Maximum Likelihood 2 Methods Comparisons and Bootstrap Tests 3 Character

Qiu, Weigang

155

Point Estimation  

NSDL National Science Digital Library

Created by Kyle Siegrist of the University of Alabama-Huntsville, this is an online, interactive lesson on point estimation. The author provides examples, exercises, and applets about the topic. More specifically, they concern estimators, method of moments, maximum likelihood, Bayes' estimators, best unbiased estimators, and sufficient, complete and ancillary statistics. Additionally, the author provides links to external resources for students looking to engage in a more in-depth study of the topic. This is simply one lesson in a series of seventeen. They are easily accessible as the author has created the site in an online textbook format.

Siegrist, Kyle

2009-02-23

156

LCLS Maximum Credible Beam Power  

SciTech Connect

The maximum credible beam power is defined as the highest credible average beam power that the accelerator can deliver to the point in question, given the laws of physics, the beam line design, and assuming all protection devices have failed. For a new accelerator project, the official maximum credible beam power is determined by project staff in consultation with the Radiation Physics Department, after examining the arguments and evidence presented by the appropriate accelerator physicist(s) and beam line engineers. The definitive parameter becomes part of the project's safety envelope. This technical note will first review the studies that were done for the Gun Test Facility (GTF) at SSRL, where a photoinjector similar to the one proposed for the LCLS is being tested. In Section 3 the maximum charge out of the gun for a single rf pulse is calculated. In Section 4, PARMELA simulations are used to track the beam from the gun to the end of the photoinjector. Finally in Section 5 the beam through the matching section and injected into Linac-1 is discussed.

Clendenin, J.

2005-01-12

157

Maximum entropy and maximum likelihood criteria for feature selection from multivariate data  

Microsoft Academic Search

We discuss several numerical methods for optimum feature selection for multivariate data based on maximum entropy and maximum likelihood criteria. Our point of view is to consider observed data x1, x2,..., xN in Rd to be samples from some unknown pdf P. We project this data onto d directions, subsequently estimate the pdf of the univariate data, then find the

Sankar Basu; Charles A. Micchelli; Peder Olsen

2000-01-01

158

Maximum Throughput in Multiple-Antenna Systems  

E-print Network

The point-to-point multiple-antenna channel is investigated in uncorrelated block fading environment with Rayleigh distribution. The maximum throughput and maximum expected-rate of this channel are derived under the assumption that the transmitter is oblivious to the channel state information (CSI), however, the receiver has perfect CSI. First, we prove that in multiple-input single-output (MISO) channels, the optimum transmission strategy maximizing the throughput is to use all available antennas and perform equal power allocation with uncorrelated signals. Furthermore, to increase the expected-rate, multi-layer coding is applied. Analogously, we establish that sending uncorrelated signals and performing equal power allocation across all available antennas at each layer is optimum. A closed form expression for the maximum continuous-layer expected-rate of MISO channels is also obtained. Moreover, we investigate multiple-input multiple-output (MIMO) channels, and formulate the maximum throughput in the asympt...

Zamani, Mahdi

2012-01-01

159

3D Dose Verification Using Tomotherapy CT Detector Array  

SciTech Connect

Purpose: To evaluate a three-dimensional dose verification method based on the exit dose using the onboard detector of tomotherapy. Methods and Materials: The study included 347 treatment fractions from 24 patients, including 10 prostate, 5 head and neck (HN), and 9 spinal stereotactic body radiation therapy (SBRT) cases. Detector sonograms were retrieved and back-projected to calculate entrance fluence, which was then forward-projected on the CT images to calculate the verification dose, which was compared with ion chamber and film measurement in the QA plans and with the planning dose in patient plans. Results: Root mean square (RMS) errors of 2.0%, 2.2%, and 2.0% were observed comparing the dose verification (DV) and the ion chamber measured point dose in the phantom plans for HN, prostate, and spinal SBRT patients, respectively. When cumulative dose in the entire treatment is considered, for HN patients, the error of the mean dose to the planning target volume (PTV) varied from 1.47% to 5.62% with a RMS error of 3.55%. For prostate patients, the error of the mean dose to the prostate target volume varied from -5.11% to 3.29%, with a RMS error of 2.49%. The RMS error of maximum doses to the bladder and the rectum were 2.34% (-4.17% to 2.61%) and 2.64% (-4.54% to 3.94%), respectively. For the nine spinal SBRT patients, the RMS error of the minimum dose to the PTV was 2.43% (-5.39% to 2.48%). The RMS error of maximum dose to the spinal cord was 1.05% (-2.86% to 0.89%). Conclusions: An excellent agreement was observed between the measurement and the verification dose. In the patient treatments, the agreement in doses to the majority of PTVs and organs at risk is within 5% for the cumulative treatment course doses. The dosimetric error strongly depends on the error in multileaf collimator leaf opening time with a sensitivity correlating to the gantry rotation period.

Sheng Ke, E-mail: ks2mc@virginia.edu [Department of Radiation Oncology, University of Virginia, Charlottesville, VA (United States); Jones, Ryan; Yang Wensha; Saraiya, Siddharth; Schneider, Bernard [Department of Radiation Oncology, University of Virginia, Charlottesville, VA (United States); Chen Quan; Sobering, Geoff; Olivera, Gustavo [TomoTherapy, Inc., Madison, WI (United States); Read, Paul [Department of Radiation Oncology, University of Virginia, Charlottesville, VA (United States)

2012-02-01

160

Patient-specific quantification of respiratory motion-induced dose uncertainty for step-and-shoot IMRT of lung cancer  

SciTech Connect

Purpose: The objective of this study was to quantify respiratory motion-induced dose uncertainty at the planning stage for step-and-shoot intensity-modulated radiation therapy (IMRT) using an analytical technique.Methods: Ten patients with stage II/III lung cancer who had undergone a planning four-dimensional (4D) computed tomographic scan and step-and-shoot IMRT planning were selected with a mix of motion and tumor size for this retrospective study. A step-and-shoot IMRT plan was generated for each patient. The maximum and minimum doses with respiratory motion were calculated for each plan, and the mean deviation from the 4D dose was calculated, taking delivery time, fractionation, and patient breathing cycle into consideration.Results: For all patients evaluated in this study, the mean deviation from the 4D dose in the planning target volume (PTV) was <2.5%, with a standard deviation <1.2%, and maximum point dose variation from the 4D dose was <6.2% in the PTV assuming delivery dose rate of 200 MU/min and patient breathing cycle of 8 s. The motion-induced dose uncertainty is a function of motion, fractionation, MU (plan modulation), dose rate, and patient breathing cycle.Conclusions: Respiratory motion-induced dose uncertainty varies from patient to patient. Therefore, it is important to evaluate the dose uncertainty on a patient-specific basis, which could be useful for plan evaluation and treatment strategy determination for selected patients.

Li, Heng; Park, Peter; Liu, Wei; Matney, Jason; Balter, Peter; Zhang, Xiaodong; Li, Xiaoqiang; Zhu, X. Ronald [Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States)] [Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States); Liao, Zhongxing [Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States)] [Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States); Li, Yupeng [Applied Research, Varian Medical Systems, Palo Alto, California 94304 (United States)] [Applied Research, Varian Medical Systems, Palo Alto, California 94304 (United States)

2013-12-15

161

A formalism for independent checking of Gamma Knife dose calculations.  

PubMed

For stereotactic radiosurgery using the Leksell Gamma Knife system, it is important to perform a pre-treatment verification of the maximum dose calculated with the Leksell GammaPlan (DLGP) stereotactic radiosurgery system. This verification can be incorporated as part of a routine quality assurance (QA) procedure to minimize the chance of a hazardous overdose. To implement this procedure, a formalism has been developed to calculate the dose DCAL(X,Y,Z,dav,t) using the following parameters: average target depth (dav), coordinates (X,Y,Z) of the maximum dose location or any other dose point(s) to be verified, 3-dimensional (3-dim) beam profiles or off-centerratios (OCR) of the four helmets, helmet size i, output factor Oi, plug factor Pi, each shot j coordinates (x,y,z)i,j, and shot treatment time (ti,j). The average depth of the target dav was obtained either from MRI/CT images or ruler measurements of the Gamma Knife Bubble Head Frame. DCAL and DLGP were then compared to evaluate the accuracy of this independent calculation. The proposed calculation for an independent check of DLGP has been demonstrated to be accurate and reliable, and thus serves as a QA tool for Gamma Knife stereotactic radiosurgery. PMID:11585215

Tsai, J S; Engler, M J; Rivard, M J; Mahajan, A; Borden, J A; Zheng, Z

2001-09-01

162

NAIRAS aircraft radiation model development, dose climatology, and initial validation  

NASA Astrophysics Data System (ADS)

The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) is a real-time, global, physics-based model used to assess radiation exposure to commercial aircrews and passengers. The model is a free-running physics-based model in the sense that there are no adjustment factors applied to nudge the model into agreement with measurements. The model predicts dosimetric quantities in the atmosphere from both galactic cosmic rays (GCR) and solar energetic particles, including the response of the geomagnetic field to interplanetary dynamical processes and its subsequent influence on atmospheric dose. The focus of this paper is on atmospheric GCR exposure during geomagnetically quiet conditions, with three main objectives. First, provide detailed descriptions of the NAIRAS GCR transport and dosimetry methodologies. Second, present a climatology of effective dose and ambient dose equivalent rates at typical commercial airline altitudes representative of solar cycle maximum and solar cycle minimum conditions and spanning the full range of geomagnetic cutoff rigidities. Third, conduct an initial validation of the NAIRAS model by comparing predictions of ambient dose equivalent rates with tabulated reference measurement data and recent aircraft radiation measurements taken in 2008 during the minimum between solar cycle 23 and solar cycle 24. By applying the criterion of the International Commission on Radiation Units and Measurements (ICRU) on acceptable levels of aircraft radiation dose uncertainty for ambient dose equivalent greater than or equal to an annual dose of 1 mSv, the NAIRAS model is within 25% of the measured data, which fall within the ICRU acceptable uncertainty limit of 30%. The NAIRAS model predictions of ambient dose equivalent rate are generally within 50% of the measured data for any single-point comparison. The largest differences occur at low latitudes and high cutoffs, where the radiation dose level is low. Nevertheless, analysis suggests that these single-point differences will be within 30% when a new deterministic pion-initiated electromagnetic cascade code is integrated into NAIRAS, an effort which is currently underway.

Mertens, Christopher J.; Meier, Matthias M.; Brown, Steven; Norman, Ryan B.; Xu, Xiaojing

2013-10-01

163

Determination of transit dose profile for a {sup 192}Ir HDR source  

SciTech Connect

Purpose: Several studies have reported methodologies to calculate and correct the transit dose component of the moving radiation source for high dose rate (HDR) brachytherapy planning systems. However, most of these works employ the average source speed, which varies significantly with the measurement technique used, and does not represent a realistic speed profile, therefore, providing an inaccurate dose determination. In this work, the authors quantified the transit dose component of a HDR unit based on the measurement of the instantaneous source speed to produce more accurate dose values. Methods: The Nucletron microSelectron-HDR Ir-192 source was characterized considering the Task Group 43 (TG-43U1) specifications. The transit dose component was considered through the calculation of the dose distribution using a Monte Carlo particle transport code, MCNP5, for each source position and correcting it by the source speed. The instantaneous source speed measurements were performed in a previous work using two optical fibers connected to a photomultiplier and an oscilloscope. Calculated doses were validated by comparing relative dose profiles with those obtained experimentally using radiochromic films. Results: TG-43U1 source parameters were calculated to validate the Monte Carlo simulations. These agreed with the literature, with differences below 1% for the majority of the points. Calculated dose profiles without transit dose were also validated by comparison with ONCENTRA{sup Registered-Sign} Brachy v. 3.3 dose values, yielding differences within 1.5%. Dose profiles obtained with MCNP5 corrected using the instantaneous source speed profile showed differences near dwell positions of up to 800% in comparison to values corrected using the average source speed, but they are in good agreement with the experimental data, showing a maximum discrepancy of approximately 3% of the maximum dose. Near a dwell position the transit dose is about 22% of the dwell dose delivered by the source dwelling 1 s and reached 104.0 cGy per irradiation in a hypothetical clinical case studied in this work. Conclusions: The present work demonstrated that the transit dose correction based on average source speed fails to accurately correct the dose, indicating that the correct speed profile should be considered. The impact on total dose due to the transit dose correction near the dwell positions is significant and should be considered more carefully in treatments with high dose rate, several catheters, multiple dwell positions, small dwell times, and several fractions.

Fonseca, G. P. [Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP, Sao Paulo 05508-000, Brazil and Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6201 BN (Netherlands); Rubo, R. A.; Santos, G. R. dos [Hospital das Clinicas da Universidade de Sao Paulo - HC/FMUSP, Sao Paulo 05403-900 (Brazil); Minamisawa, R. A. [Laboratory for Micro- and Nanotechnology Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Antunes, P. C. G.; Yoriyaz, H. [Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP, Sao Paulo 05508-000 (Brazil)

2013-05-15

164

Esophageal tolerance to high-dose stereotactic ablative radiotherapy.  

PubMed

Dose-volume parameters are needed to guide the safe administration of stereotactic ablative radiotherapy (SABR). We report on esophageal tolerance to high-dose hypofractionated radiation in patients treated with SABR. Thirty-one patients with spine or lung tumors received single- or multiple-fraction SABR to targets less than 1 cm from the esophagus. End points evaluated include D(5cc) (minimum dose in Gy to 5 cm(3) of the esophagus receiving the highest dose), D(2cc) , D(1cc) , and D(max) (maximum dose to 0.01 cm(3) ). Multiple-fraction treatments were correlated using the linear quadratic and linear quadratic-linear/universal survival models. Three esophageal toxicity events occurred, including esophagitis (grade 2), tracheoesophageal fistula (grade 4-5), and esophageal perforation (grade 4-5). Chemotherapy was a cofactor in the high-grade events. The median time to development of esophageal toxicity was 4.1 months (range 0.6-6.1 months). Two of the three events occurred below a published D(5cc) threshold, all three were below a D(2cc) threshold, and one was below a D(max) threshold. We report a dosimetric analysis of incidental dose to the esophagus from SABR. High-dose hypofractionated radiotherapy led to a number of high-grade esophageal adverse events, suggesting that conservative parameters to protect the esophagus are necessary when SABR is used, especially in the setting of chemotherapy or prior radiotherapy. PMID:22168251

Abelson, J A; Murphy, J D; Loo, B W; Chang, D T; Daly, M E; Wiegner, E A; Hancock, S; Chang, S D; Le, Q-T; Soltys, S G; Gibbs, I C

2012-01-01

165

The Solar Maximum observatory  

NASA Technical Reports Server (NTRS)

The successful retrieval and repair of the Solar Maximum Mission (SMM) satellite by Shuttle astronauts in April 1984 permitted continuance of solar flare observations that began in 1980. The SMM carries a soft X ray polychromator, gamma ray, UV and hard X ray imaging spectrometers, a coronagraph/polarimeter and particle counters. The data gathered thus far indicated that electrical potentials of 25 MeV develop in flares within 2 sec of onset. X ray data show that flares are composed of compressed magnetic loops that have come too close together. Other data have been taken on mass ejection, impacts of electron beams and conduction fronts with the chromosphere and changes in the solar radiant flux due to sunspots.

Rust, D. M.

1984-01-01

166

Minimum Convex Partitions and Maximum Empty Polytopes  

E-print Network

Let S be a set of n points in d-space. A convex Steiner partition is a tiling of CH(S) with empty convex bodies. For every integer d, we show that S admits a convex Steiner partition with at most (n-1)/d tiles. This bound is the best possible for affine independent points in the plane, and it is best possible apart from constant factors in every dimension d>= 3. We also give the first constant-factor approximation algorithm for computing a minimum Steiner convex partition of an affine independent point set in the plane. Determining the maximum possible volume of a single tile in a Steiner partition is equivalent to a famous problem of Danzer and Rogers. We give a (1-epsilon)-approximation for the maximum volume of an empty convex body when S lies in the d-dimensional unit box [0,1]^d.

Dumitrescu, Adrian; Tóth, Csaba D

2011-01-01

167

Experimental Evaluation of the Impact of Different Head-and-Neck Intensity-Modulated Radiation Therapy Planning Techniques on Doses to the Skin and Shallow Targets  

SciTech Connect

Purpose: To investigate experimentally the impact of different head-and-neck intensity-modulated radiation therapy (IMRT) planning techniques on doses to the skin and shallow targets. Methods and Materials: A semicylindrical phantom was constructed with micro-MOSFET dosimeters (Thomson-Nielson, Ottawa, Ontario, Canada) at 0-, 3-, 6-, 9-, and 12-mm depths. The planning target volume (PTV) was pulled back 0, 3, or 5 mm from the body contour. The IMRT plans were created to maximize PTV coverage, with one of the following strategies: (a) aim for a maximum 110% hotspot, with 115% allowed; (b) aims for a maximum 105% hotspot; (c) aims for a maximum 105% hotspot and 50% of skin to get a maximum 70% of the prescribed dose; and (d) aim for 99% of the PTV volume to receive 90-93% of prescribed dose, with a maximum 105% hotspot, and with the dose to the skin structure minimized. Doses delivered using a linear accelerator were measured. Setup uncertainty was simulated by intentionally shifting the phantom in a range of {+-}8 mm, and calculating the delivered dose for a range of systematic and random uncertainties. Results: From lowest to highest skin dose, the planning strategies were in the order of c, d, b, and a, but c showed a tendency to underdose tissues at depth. Delivered doses varied by 10-20%, depending on planning strategy. For typical setup uncertainties, cumulative dose reduction to a point 6 mm deep was <4%. Conclusions: It is useful to use skin as a sensitive structure, but a minimum dose constraint must be used for the PTV if unwanted reductions in dose to nodes near the body surface are to be avoided. Setup uncertainties are unlikely to give excessive reductions in cumulative dose.

Court, Laurence E. [Department of Radiation Oncology, Dana-Farber and Brigham and Women's Cancer Center, Boston, MA (United States)], E-mail: lcourt@lroc.harvard.edu; Tishler, Roy B. [Department of Radiation Oncology, Dana-Farber and Brigham and Women's Cancer Center, Boston, MA (United States)

2007-10-01

168

A dosimetric comparison of different treatment plans of palliative spinal bone irradiation: analysis of dose coverage with respect to ICRU 50 report  

PubMed Central

Background This study aimed to analyze three-dimensional (3D) dosimetric data of conventional two-dimensional (2D) palliative spinal bone irradiation using different reference points and treatment plans with respect to the International Commission on Radiation Units and Measurements (ICRU) Report 50. Methods Forty-five simulation CT scans of 39 patients previously treated for thoraco-lumbar spinal bone metastases were used. Three different treatment plans were created: (1) single posterior field plans using the ICRU reference points (ICRUrps); (2) single posterior field plans using the International Bone Metastasis Consensus Working Party reference points (IBMCrps); (3) two opposed anterior-posterior (AP-PA) field plans using the ICRUrps. The intended dose range for planning target volume (PTV) was 90% to 110% of the prescribed dose for AP-PA field plans. Cumulative dose-volume histograms were generated for each plan, and minimum, maximum and mean doses to the PTV, medulla spinalis, esophagus and intestines were analyzed. Results The mean percentages of minimum, maximum and mean PTV doses ± standard deviation were, respectively, 91 ± 1.3%, 108.8 ± 1.3% and 99.7 ± 1.3% in AP-PA field plans; 77.3 ± 2.6%, 122.2 ± 4.3% and 99.8 ± 2.6% in ICRUrp single field plans; and 83.7 ± 3.3%, 133.9 ± 7.1% and 108.8 ± 3.3% in IBMCrp single field plans. Minimum doses of both single field plans were significantly lower (p < 0.001) while maximum doses were significantly higher (p < 0.001) than AP-PA field plans. Minimum, maximum and mean doses were higher in IBMCrp single field plans than in ICRUrp single field plans (p < 0.001). The mean medulla spinalis doses were lower in AP-PA field plans than single posterior field plans (p < 0.001). Maximum doses for medulla spinalis were higher than 120% of the prescribed dose in 22 of 45 (49%) IBMCrp single field plans. Mean esophagus and intestinal doses were higher (p < 0.001) in AP-PA field plans than single field plans, however, less than 95% of the prescribed dose. Conclusion In palliative spinal bone irradiation, 2D conventional single posterior field radiotherapy did not accomplish the ICRU Report 50 recommendations for PTV dose distribution, while the AP-PA field plans did achieve the intended dose ranges with a homogenous distribution and reasonable doses to the medulla spinalis, esophagus and intestines. PMID:19128500

Andic, Fundagul; Baz Cifci, Sule; Ors, Yasemin; Niang, Umar; Dirier, Ahmet; Adli, Mustafa

2009-01-01

169

Impact of the number of control points has on isodose distributions in a dynamic multileaf collimator intensity-modulated radiation therapy delivery  

SciTech Connect

Intensity-modulated radiation therapy (IMRT) is a powerful technique in planning the delivery of dose. The most common IMRT delivery requires the use of moving multileaf collimators (MLCs) to deliver the requested fluence pattern. A dynamic delivery IMRT field file will contain several control points that are defined MLC shapes at a marked fraction of the delivered monitor units. The size of this file and the fidelity of the deliverable fluence are proportional to the number of control points defined. This study investigates the effect of reducing the number of control points has on the resultant dose distribution quality in complex IMRT in efforts to reduce transfer times, loading times, check sum times and file storage. Analysis was performed with 6 head and neck patients on an Eclipse version 8.5 treatment planning system (Varian, Palo Alto, CA). To ensure the quality of all treatments, Eclipse defines a minimum of 64 and a maximum of 320 control points per subfield (Eclipse Algorithms Reference guide). All 6 patients' plans were calculated with fixed 64, 166, and 320 control points using the sliding window technique. In addition, each plan was calculated in variable mode (Normal mode) in which the planning system determined the required number of control points. Each of the 4 plans for each patient was renormalized to provide the same mean planning target volume (PTV) 70 dose. Dose values for critical and target structures were examined for each patient. When examining the minimum, maximum, and mean doses to all target structures, it was noted that the greatest reduction in target dose coverage caused by reduced number of control points was 0.5%, which occurred for the minimum dose to the PTV56 structure in one plan.' Dose analysis for critical structures showed no clinically significant increase in dose when compared with the 320 control point plan.

Goraj, Andrew [Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY (United States); Boer, Steven F. de, E-mail: steven.deboer@roswellpark.org [Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY (United States); Department of Physiology and Biophysics, State University of New York at Buffalo, NY (United States)

2012-01-01

170

Factors Associated With Chest Wall Toxicity After Accelerated Partial Breast Irradiation Using High-Dose-Rate Brachytherapy  

SciTech Connect

Purpose: The purpose of this analysis was to evaluate dose-volume relationships associated with a higher probability for developing chest wall toxicity (pain) after accelerated partial breast irradiation (APBI) by using both single-lumen and multilumen brachytherapy. Methods and Materials: Rib dose data were available for 89 patients treated with APBI and were correlated with the development of chest wall/rib pain at any point after treatment. Ribs were contoured on computed tomography planning scans, and rib dose-volume histograms (DVH) along with histograms for other structures were constructed. Rib DVH data for all patients were sampled at all volumes {>=}0.008 cubic centimeter (cc) (for maximum dose related to pain) and at volumes of 0.5, 1, 2, and 3 cc for analysis. Rib pain was evaluated at each follow-up visit. Patient responses were marked as yes or no. No attempt was made to grade responses. Eighty-nine responses were available for this analysis. Results: Nineteen patients (21.3%) complained of transient chest wall/rib pain at any point in follow-up. Analysis showed a direct correlation between total dose received and volume of rib irradiated with the probability of developing rib/chest wall pain at any point after follow-up. The median maximum dose at volumes {>=}0.008 cc of rib in patients who experienced chest wall pain was 132% of the prescribed dose versus 95% of the prescribed dose in those patients who did not experience pain (p = 0.0035). Conclusions: Although the incidence of chest wall/rib pain is quite low with APBI brachytherapy, attempts should be made to keep the volume of rib irradiated at a minimum and the maximum dose received by the chest wall as low as reasonably achievable.

Brown, Sheree, E-mail: shereedst32@hotmail.com [Department of Radiation Oncology, WellStar Kennestone Hospital, Marietta, Georgia (United States); Vicini, Frank [Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, Michigan (United States); Vanapalli, Jyotsna R.; Whitaker, Thomas J.; Pope, D. Keith [Department of Radiation Oncology, WellStar Kennestone Hospital, Marietta, Georgia (United States); Lyden, Maureen [BioStat International, Inc., Tampa, Florida (United States); Bruggeman, Lisa; Haile, Kenneth L.; McLaughlin, Mark P. [Department of Radiation Oncology, WellStar Kennestone Hospital, Marietta, Georgia (United States)

2012-07-01

171

The contribution from transit dose for 192Ir HDR brachytherapy treatments  

NASA Astrophysics Data System (ADS)

Brachytherapy treatment planning systems that use model-based dose calculation algorithms employ a more accurate approach that replaces the TG43-U1 water dose formalism and adopt the TG-186 recommendations regarding composition and geometry of patients and other relevant effects. However, no recommendations were provided on the transit dose due to the source traveling inside the patient. This study describes a methodology to calculate the transit dose using information from the treatment planning system (TPS) and considering the source's instantaneous and average speed for two prostate and two gynecological cases. The trajectory of the 192Ir HDR source was defined by importing applicator contour points and dwell positions from the TPS. The transit dose distribution was calculated using the maximum speed, the average speed and uniform accelerations obtained from the literature to obtain an approximate continuous source distribution simulated with a Monte Carlo code. The transit component can be negligible or significant depending on the speed profile adopted, which is not clearly reported in the literature. The significance of the transit dose can also be due to the treatment modality; in our study interstitial treatments exhibited the largest effects. Considering the worst case scenario the transit dose can reach 3% of the prescribed dose in a gynecological case with four catheters and up to 11.1% when comparing the average prostate dose for a case with 16 catheters. The transit dose component increases by increasing the number of catheters used for HDR brachytherapy, reducing the total dwell time per catheter or increasing the number of dwell positions with low dwell times. This contribution may become significant (>5%) if it is not corrected appropriately. The transit dose cannot be completely compensated using simple dwell time corrections since it may have a non-uniform distribution. An accurate measurement of the source acceleration and maximum speed should be incorporated in clinical practice or provided by the manufacturer to determine the transit dose component with high accuracy.

Fonseca, G. P.; Landry, G.; Reniers, B.; Hoffmann, A.; Rubo, R. A.; Antunes, P. C. G.; Yoriyaz, H.; Verhaegen, F.

2014-04-01

172

Measurements of individual radiation doses in residents living around the Fukushima Nuclear Power Plant.  

PubMed

At the outset of the accident at Fukushima Daiichi Nuclear Power Plant in March 2011, the radiation doses experienced by residents were calculated from the readings at monitoring posts, with several assumptions being made from the point of view of protection and safety. However, health effects should also be estimated by obtaining measurements of the individual radiation doses. The individual external radiation doses, determined by a behavior survey in the "evacuation and deliberate evacuation area" in the first 4 months, were <5 mSv in 97.4% of residents (maximum: 15 mSv). Doses in Fukushima Prefecture were <3 mSv in 99.3% of 386,572 residents analyzed. External doses in Fukushima City determined by personal dosimeters were <1 mSv/3 months (September-November, 2011) in 99.7% of residents (maximum: 2.7 mSv). Thyroid radiation doses, determined in March using a NaI (TI) scintillation survey meter in children in the evacuation and deliberate evacuation area, were <10 mSv in 95.7% of children (maximum: 35 mSv). Therefore, all doses were less than the intervention level of 50 mSv proposed by international organizations. Internal radiation doses determined by cesium-134 ((134)C) and cesium-137 ((137)C) whole-body counters (WBCs) were <1 mSv in 99% of the residents, and the maximum thyroid equivalent dose by iodine-131 WBCs was 20 mSv. The exploratory committee of the Fukushima Health Management Survey mentions on its website that radiation from the accident is unlikely to be a cause of adverse health effects in the future. In any event, sincere scientific efforts must continue to obtain individual radiation doses that are as accurate as possible. However, observation of the health effects of the radiation doses described above will require reevaluation of the protocol used for determining adverse health effects. The dose-response relationship is crucial, and the aim of the survey should be to collect sufficient data to confirm the presence or absence of radiation health effects. In particular, the schedule of decontamination needs reconsideration. The decontamination map is determined based on the results of airborne monitoring and the radiation dose calculated from readings taken at the monitoring posts at the initial period of the accident. The decontamination protocol should be reevaluated based on the individual doses of the people who desire to live in those areas. PMID:24131040

Nagataki, Shigenobu; Takamura, Noboru; Kamiya, Kenji; Akashi, Makoto

2013-11-01

173

Maximum likelihood deconvolution: a new perspective  

SciTech Connect

Maximum-likelihood deconvolution can be presented from at least two very different points of view. Unfortunately, in most journal articles, it is couched in the mystique of state-variable models and estimation theory, both of which, are generally quite foreign to geophysical signal processors. This paper explains maximum-likelihood deconvolution using the well-known convolutional model and some relatively simple ideas from optimization theory. Both of these areas should be well known to geophysical signal processors. Although it is straightforward to develop the theory of maximum-likelihood deconvolution using the convolutional model and optimization theory, this approach does not lead to practical computational algorithms. Recursive algorithms must be used; they are orders of magnitude faster than the batch algorithms that are associated with the convolutional model.

Mendel, J.M.

1988-03-01

174

Dose Calculations for [131I] Meta-Iodobenzylguanidine-Induced Bystander Effects  

PubMed Central

Targeted radiotherapy is a potentially useful treatment for some cancers and may be potentiated by bystander effects. However, without estimation of absorbed dose, it is difficult to compare the effects with conventional external radiation treatment. Methods: Using the Vynckier – Wambersie dose point kernel, a model for dose rate evaluation was created allowing for calculation of absorbed dose values to two cell lines transfected with the noradrenaline transporter (NAT) gene and treated with [131I]MIBG. Results: The mean doses required to decrease surviving fractions of UVW/NAT and EJ138/NAT cells, which received medium from [131I]MIBG-treated cells, to 25 – 30% were 1.6 and 1.7 Gy respectively. The maximum mean dose rates achieved during [131I]MIBG treatment were 0.09 – 0.75 Gy/h for UVW/NAT and 0.07 – 0.78 Gy/h for EJ138/NAT. These were significantly lower than the external beam gamma radiation dose rate of 15 Gy/h. In the case of control lines which were incapable of [131I]MIBG uptake the mean absorbed doses following radiopharmaceutical were 0.03 – 0.23 Gy for UVW and 0.03 – 0.32 Gy for EJ138. Conclusion: [131I]MIBG treatment for ICCM production elicited a bystander dose-response profile similar to that generated by external beam gamma irradiation but with significantly greater cell death. PMID:24659931

Gow, M. D.; Seymour, C. B.; Boyd, M.; Mairs, R. J.; Prestiwch, W. V.; Mothersill, C. E.

2014-01-01

175

Estimation Of Organ Doses From Solar Particle Events For Future Space Exploration Missions  

NASA Technical Reports Server (NTRS)

Radiation protection practices define the effective dose as a weighted sum of equivalent dose over major organ sites for radiation cancer risks. Since a crew personnel dosimeter does not make direct measurement of the effective dose, it has been estimated with skin-dose measurements and radiation transport codes for ISS and STS missions. If sufficient protection is not provided near solar maximum, the radiation risk can be significant due to exposure to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR) on future exploratory-class and long-duration missions. For accurate estimates of overall fatal cancer risks from SPEs, the specific doses at various blood forming organs (BFOs) were considered, because proton fluences and doses vary considerably across marrow regions. Previous estimates of BFO doses from SPEs have used an average body-shielding distribution for the bone marrow based on the computerized anatomical man model (CAM). With the development of an 82-point body-shielding distribution at BFOs, the mean and variance of SPE doses in the major active marrow regions (head and neck, chest, abdomen, pelvis and thighs) will be presented. Consideration of the detailed distribution of bone marrow sites is one of many requirements to improve the estimation of effective doses for radiation cancer risks.

Kim, Myung-Hee; Cucinotta, Francis A.

2006-01-01

176

Theoretical considerations for SRAM total-dose hardening  

SciTech Connect

The theoretical hardness against total dose of the six-transistor SRAM cell is investigated in detail. An explicit analytical expression of the maximum tolerable threshold voltage shift is derived for two cross-coupled inverters. A numerical method is used to explore the hardness of the read and write operations. Both N- and P-channel access transistors designs are considered and their respective advantages are compared. The study points out that the radiation hardness mainly relies on the technology. Results obtained with the very robust Gate-All-Around process are finally presented.

Francis, P.; Flandre, D.; Colinge, J.P. [Univ. Catholique de Louvain, Louvain-la-Neuve (Belgium)] [Univ. Catholique de Louvain, Louvain-la-Neuve (Belgium)

1995-04-01

177

Radiological Dose Assessment 8 2007 Site environmental report8-  

E-print Network

Radiological Dose Assessment 8 2007 Site environmental report8- DRAFT Brookhaven National that the overall radiological dose impact to members of the public, workers, visitors, and the environment is "As radiological dose to the public is calculated at the site boundary as the "maximum" dose that could be received

178

The Radiation Dose-Response of the Human Spinal Cord  

SciTech Connect

Purpose: To characterize the radiation dose-response of the human spinal cord. Methods and Materials: Because no single institution has sufficient data to establish a dose-response function for the human spinal cord, published reports were combined. Requisite data were dose and fractionation, number of patients at risk, number of myelopathy cases, and survival experience of the population. Eight data points for cervical myelopathy were obtained from five reports. Using maximum likelihood estimation correcting for the survival experience of the population, estimates were obtained for the median tolerance dose, slope parameter, and {alpha}/{beta} ratio in a logistic dose-response function. An adequate fit to thoracic data was not possible. Hyperbaric oxygen treatments involving the cervical cord were also analyzed. Results: The estimate of the median tolerance dose (cervical cord) was 69.4 Gy (95% confidence interval, 66.4-72.6). The {alpha}/{beta} = 0.87 Gy. At 45 Gy, the (extrapolated) probability of myelopathy is 0.03%; and at 50 Gy, 0.2%. The dose for a 5% myelopathy rate is 59.3 Gy. Graphical analysis indicates that the sensitivity of the thoracic cord is less than that of the cervical cord. There appears to be a sensitizing effect from hyperbaric oxygen treatment. Conclusions: The estimate of {alpha}/{beta} is smaller than usually quoted, but values this small were found in some studies. Using {alpha}/{beta} = 0.87 Gy, one would expect a considerable advantage by decreasing the dose/fraction to less than 2 Gy. These results were obtained from only single fractions/day and should not be applied uncritically to hyperfractionation.

Schultheiss, Timothy E. [Department of Radiation Oncology, City of Hope Cancer Center, Duarte, CA (United States)], E-mail: schultheiss@coh.org

2008-08-01

179

Secondary Neutron Doses for Several Beam Configurations for Proton Therapy  

SciTech Connect

Purpose: To compare possible neutron doses produced in scanning and scattering modes, with the latter assessed using a newly built passive-scattering proton beam line. Methods and Materials: A 40 x 30.5 x 30-cm water phantom was irradiated with 230-MeV proton beams using a gantry angle of 270{sup o}, a 10-cm-diameter snout, and a brass aperture with a diameter of 7 cm and a thickness of 6.5 cm. The secondary neutron doses during irradiation were measured at various points using CR-39 detectors, and these measurements were cross-checked using a neutron survey meter with a 22-cm range and a 5-cm spread-out Bragg peak. Results: The maximum doses due to secondary neutrons produced by a scattering beam-delivery system were on the order of 0.152 mSv/Gy and 1.17 mSv/Gy at 50 cm from the beam isocenter in the longitudinal (0{sup o}) and perpendicular (90{sup o}) directions, respectively. The neutron dose equivalent to the proton absorbed dose, measured from 10 cm to 100 cm from the isocenter, ranged from 0.071 mSv/Gy to 1.96 mSv/Gy in the direction of the beam line (i.e., {phi} = 0 deg.). The largest neutron dose, of 3.88 mSv/Gy, was observed at 135{sup o} and 25 cm from the isocenter. Conclusions: Although the secondary neutron doses in proton therapy were higher when a scattering mode rather than a scanning mode was used, they did not exceed the scattered photon dose in typical photon treatments.

Shin, Dongho; Yoon, Myonggeun; Kwak, Jungwon; Shin, Jungwook [Proton Therapy Center, National Cancer Center, Goyang (Korea, Republic of); Lee, Se Byeong [Proton Therapy Center, National Cancer Center, Goyang (Korea, Republic of)], E-mail: sblee@ncc.re.kr; Park, Sung Yong [Proton Therapy Center, National Cancer Center, Goyang (Korea, Republic of); Park, Soah [Department of Radiation Oncology, Kangnam Sacred Heart Hospital, Seoul (Korea, Republic of); Kim, Dae Yong; Cho, Kwan Ho [Proton Therapy Center, National Cancer Center, Goyang (Korea, Republic of)

2009-05-01

180

Dose error from deviation of dwell time and source position for high dose-rate 192Ir in remote afterloading system.  

PubMed

The influence of deviations in dwell times and source positions for (192)Ir HDR-RALS was investigated. The potential dose errors for various kinds of brachytherapy procedures were evaluated. The deviations of dwell time ?T of a (192)Ir HDR source for the various dwell times were measured with a well-type ionization chamber. The deviations of source position ?P were measured with two methods. One is to measure actual source position using a check ruler device. The other is to analyze peak distances from radiographic film irradiated with 20 mm gap between the dwell positions. The composite dose errors were calculated using Gaussian distribution with ?T and ?P as 1? of the measurements. Dose errors depend on dwell time and distance from the point of interest to the dwell position. To evaluate the dose error in clinical practice, dwell times and point of interest distances were obtained from actual treatment plans involving cylinder, tandem-ovoid, tandem-ovoid with interstitial needles, multiple interstitial needles, and surface-mold applicators. The ?T and ?P were 32 ms (maximum for various dwell times) and 0.12 mm (ruler), 0.11 mm (radiographic film). The multiple interstitial needles represent the highest dose error of 2%, while the others represent less than approximately 1%. Potential dose error due to dwell time and source position deviation can depend on kinds of brachytherapy techniques. In all cases, the multiple interstitial needles is most susceptible. PMID:24566719

Okamoto, Hiroyuki; Aikawa, Ako; Wakita, Akihisa; Yoshio, Kotaro; Murakami, Naoya; Nakamura, Satoshi; Hamada, Minoru; Abe, Yoshihisa; Itami, Jun

2014-07-01

181

Maximum entropy discrimination Tommi Jaakkola  

E-print Network

;) that maximizes the entropy H(P ) subject to the classi#12;cation constraints R P(#2;) [ y t L(X t j#2;) ] d#2Maximum entropy discrimination Tommi Jaakkola MIT AI Lab 545 Technology Sq. Cambridge, MA 02139 framework for discriminative estimation based on the maximum entropy principle and its extensions. All

Jaakkola, Tommi S.

182

PRECEDENTS FOR AUTHORIZATION OF CONTENTS USING DOSE RATE MEASUREMENTS  

SciTech Connect

For the transportation of Radioactive Material (RAM) packages, the requirements for the maximum allowed dose rate at the package surface and in its vicinity are given in Title 10 of the Code of Federal Regulations, Section 71.47. The regulations are based on the acceptable dose rates to which the public, workers, and the environment may be exposed. As such, the regulations specify dose rates, rather than quantity of radioactive isotopes and require monitoring to confirm the requirements are met. 10CFR71.47 requires that each package of radioactive materials offered for transportation must be designed and prepared for shipment so that under conditions normally incident to transportation the radiation level does not exceed 2 mSv/h (200 mrem/h) at any point on the external Surface of the package, and the transport index does not exceed 10. Before shipment, the dose rate of the package is determined by measurement, ensuring that it conforms to the regulatory limits, regardless of any analyses. This is the requirement for all certified packagings. This paper discusses the requirements for establishing the dose rates when shipping RAM packages and the precedents for meeting these requirements by measurement.

Abramczyk, G.; Bellamy, S.; Nathan, S.; Loftin, B.

2012-06-05

183

CT based three dimensional dose-volume evaluations for high-dose rate intracavitary brachytherapy for cervical cancer  

PubMed Central

Background In this study, high risk clinical target volumes (HR-CTVs) according to GEC-ESTRO guideline were contoured retrospectively based on CT images taken at the time of high-dose rate intracavitary brachytherapy (HDR-ICBT) and correlation between clinical outcome and dose of HR-CTV were analyzed. Methods Our study population consists of 51 patients with cervical cancer (Stages IB-IVA) treated with 50 Gy external beam radiotherapy (EBRT) using central shield combined with 2–5 times of 6 Gy HDR-ICBT with or without weekly cisplatin. Dose calculation was based on Manchester system and prescribed dose of 6 Gy were delivered for point A. CT images taken at the time of each HDR-ICBT were reviewed and HR-CTVs were contoured. Doses were converted to the equivalent dose in 2 Gy (EQD2) by applying the linear quadratic model (?/??=?10 Gy). Results Three-year overall survival, Progression-free survival, and local control rate was 82.4%, 85.3% and 91.7%, respectively. Median cumulative dose of HR-CTV D90 was 65.0 Gy (52.7-101.7 Gy). Median length from tandem to the most lateral edge of HR-CTV at the first ICBT was 29.2 mm (range, 18.0-51.9 mm). On univariate analysis, both LCR and PFS was significantly favorable in those patients D90 for HR-CTV was 60 Gy or greater (p?=?0.001 and 0.03, respectively). PFS was significantly favorable in those patients maximum length from tandem to edge of HR-CTV at first ICBT was shorter than 3.5 cm (p?=?0.042). Conclusion Volume-dose showed a relationship to the clinical outcome in CT based brachytherapy for cervical carcinoma. PMID:24938757

2014-01-01

184

Preliminary liver dose estimation in the new facility for biomedical applications at the RA-3 reactor.  

PubMed

As a part of the project concerning the irradiation of a section of the human liver left lobe, a preliminary estimation of the expected dose was performed. To obtain proper input values for the calculation, neutron flux and gamma dose rate characterization were carried out using adequate portions of cow or pig liver covered with demineralized water simulating the preservation solution. Irradiations were done inside a container specially designed to fulfill temperature preservation of the organ and a reproducible irradiation position (which will be of importance for future planification purposes). Implantable rhodium based self-powered neutron detectors were developed to obtain neutron flux profiles both external and internal. Implantation of SPND was done along the central longitudinal axis of the samples, where lowest flux is expected. Gamma dose rate was obtained using a neutron shielded graphite ionization chamber moved along external surfaces of the samples. The internal neutron profile resulted uniform enough to allow for a single and static irradiation of the liver. For dose estimation, irradiation condition was set in order to obtain a maximum of 15 Gy-eq in healthy tissue. Additionally, literature reported boron concentrations of 47 ppm in tumor and 8 ppm in healthy tissue and a more conservative relationship (30/10 ppm) were used. To make a conservative estimation of the dose the following considerations were done: i). Minimum measured neutron flux inside the sample (approximately 5 x 10(9) n cm-2 s-1) was considered to calculate dose in tumor. (ii). Maximum measured neutron flux (considering both internal as external profiles) was used to calculate dose in healthy tissue (approximately 8.7 x 10(9) n cm-2 s-1). (iii). Maximum measured gamma dose rate (approximately 13.5 Gy h-1) was considered for both tumor and healthy tissue. Tumor tissue dose was approximately 69 Gy-eq for 47 ppm of (10)B and approximately 42 Gy-eq for 30 ppm, for a maximum dose of 15 Gy-eq in healthy tissue. As can be seen from these results, even for the most conservative case, minimum tumor dose will be acceptable from the treatment point of view, which shows that the irradiation conditions at this facility have quite good characteristics for the proposed irradiation. PMID:19394239

Gadan, M; Crawley, V; Thorp, S; Miller, M

2009-07-01

185

Utirik Atoll Dose Assessment  

SciTech Connect

On March 1, 1954, radioactive fallout from the nuclear test at Bikini Atoll code-named BRAVO was deposited on Utirik Atoll which lies about 187 km (300 miles) east of Bikini Atoll. The residents of Utirik were evacuated three days after the fallout started and returned to their atoll in May 1954. In this report we provide a final dose assessment for current conditions at the atoll based on extensive data generated from samples collected in 1993 and 1994. The estimated population average maximum annual effective dose using a diet including imported foods is 0.037 mSv y{sup -1} (3.7 mrem y{sup -1}). The 95% confidence limits are within a factor of three of their population average value. The population average integrated effective dose over 30-, 50-, and 70-y is 0.84 mSv (84, mrem), 1.2 mSv (120 mrem), and 1.4 mSv (140 mrem), respectively. The 95% confidence limits on the population-average value post 1998, i.e., the 30-, 50-, and 70-y integral doses, are within a factor of two of the mean value and are independent of time, t, for t > 5 y. Cesium-137 ({sup 137}Cs) is the radionuclide that contributes most of this dose, mostly through the terrestrial food chain and secondarily from external gamma exposure. The dose from weapons-related radionuclides is very low and of no consequence to the health of the population. The annual background doses in the U. S. and Europe are 3.0 mSv (300 mrem), and 2.4 mSv (240 mrem), respectively. The annual background dose in the Marshall Islands is estimated to be 1.4 mSv (140 mrem). The total estimated combined Marshall Islands background dose plus the weapons-related dose is about 1.5 mSv y{sup -1} (150 mrem y{sup -1}) which can be directly compared to the annual background effective dose of 3.0 mSv y{sup -1} (300 mrem y{sup -1}) for the U. S. and 2.4 mSv y{sup -1} (240 mrem y{sup -1}) for Europe. Moreover, the doses listed in this report are based only on the radiological decay of {sup 137}Cs (30.1 y half-life) and other radionuclides. However, we continually see {sup 137}Cs in the groundwater at all contaminated atolls; the turnover time of the groundwater is about 5 y. The {sup 137}Cs can only get to the groundwater by leaching through the soil column when a portion of the soluble fraction of {sup 137}Cs inventory in the soil is transported to the groundwater when rainfall is heavy enough to cause recharge of the aquifer. This process is causing a loss of {sup 137}Cs out of the root zone of the plants that provides an environmental loss constant ({lambda}{sub env}) in addition to radiological decay {lambda}{sub rad}. Consequently, there is an effective rate of loss, {lambda}{sub eff} = {lambda}{sub rad} + {lambda}{sub env} that is the sum of the radiological and environmental-loss decay constants. We have had, and continue to have, a vigorous program to determine the rate of the environmental loss process. What we do know at this time is that the loss of {sup 137}Cs over time is greater than the estimate based on radiological decay only, and that the actual dose received by the Utirik people over 30-, 50-, or 70-y will be less than those presented in this report.

Robison, W.L.; Conrado, C.L.; Bogen, K.T

1999-10-06

186

Dose gradient impact on equivalent dose at 2 Gy for high dose rate interstitial brachytherapy  

PubMed Central

Purpose To evaluate a new calculation model estimating the equivalent dose at 2 Gy (EQD2) taking into account dose gradient in high dose rate interstitial brachytherapy (HDRIB). Material and methods Forty dose-volume histograms (DVHs) of breast (20 pts) and prostate (20 pts) cancer dose distributions were reviewed. Physical prescribed doses (PPD) were 34 Gy (10f/5d) and 18 Gy (6f/2d) for breast (partial irradiation protocol) and prostate (boost after external irradiation) treatment, respectively. For each DVH, clinical target volume (CTV), V100, V150, V200, D90 and D100 were determined. Based on DVH segmentation, elementary doses (d) delivered to elementary volumes were determined, then multiplied by C (% of CTV receiving d). According to the linear quadratic model, EQD2 was calculated for different ?/? ratios. Results For breast implant, median EQD2 (?/? = 4) was 42 Gy and 76 Gy (66-85) without and with dose gradient consideration, respectively. For prostate implant, median EQD2 (?/? = 1.5) was 39 Gy and 98 Gy (90-103) whether dose gradient was not or was taken into account, respectively. Conclusions This study pointed out that for brachytherapy, EQD2 calculation must take into account the dose gradient. Because this model is a mathematical one, it has to be cautiously applied. Nevertheless, it appears as a useful tool for EQD2 comparison between the same PPD delivered through EBRT or brachytherapy regarding trial result interpretation. PMID:23346135

Hannoun-Levi, Jean-Michel; Chand-Fouche, Marie-Eve; Dejean, Catherine

2012-01-01

187

Radiation measurements and doses at SST altitudes  

NASA Technical Reports Server (NTRS)

Radiation components and dose equivalents due to galactic and solar cosmic rays in the high atmosphere, especially at SST altitudes, are presented. The dose equivalent rate for the flight personnel flying 500 hours per year in cruise altitudes of 60,000-65,000 feet (18-19.5 km) in high magnetic latitudes is about 0.75-1.0 rem per year averaged over the solar cycle, or about 15-20 percent of the maximum permissible dose rate.

Foelsche, T.

1972-01-01

188

The 1988 Solar Maximum Mission event list  

NASA Technical Reports Server (NTRS)

Information on solar burst and transient activity observed by the Solar Maximum Mission (SMM) during 1988 pointed observations is presented. Data from the following SMM experiments are included: (1) gamma ray spectrometer; (2) hard x ray burst spectrometer; (3) flat crystal spectrometers; (4) bent crystal spectrometer; (5) ultraviolet spectrometer polarimeter; and (6) coronagraph/polarimeter. Correlative optical, radio, and Geostationary Operational Environmental Satellite (GOES) x ray data are also presented. Where possible, bursts, or transients observed in the various wavelengths were grouped into discrete flare events identified by unique event numbers. Each event carries a qualifier denoting the quality or completeness of the observation. Spacecraft pointing coordinates and flare site angular displacement values from sun center are also included.

Dennis, B. R.; Licata, J. P.; Tolbert, A. K.

1992-01-01

189

An empirical model for independent dose verification of the Gamma Knife treatment planning.  

PubMed

A formalism for an independent dose verification of the Gamma Knife treatment planning is developed. It is based on the approximation that isodose distribution for a single shot is in the shape of an ellipsoid in three-dimensional space. The dose profiles for a phantom along each of the three major axes are fitted to a function which contains the terms that represent the contributions from a point source, an extrafocal scattering, and a flat background. The fitting parameters are extracted for all four helmet collimators, at various shot locations, and with different skull shapes. The 33 parameters of a patient's skull shape obtained from the Skull Scaling Instrument measurements are modeled for individual patients. The relative doses for a treatment volume in the form of 31 x 31 x 31 matrix of points are extracted from the treatment planning system, the Leksell Gamma-Plan (LGP). Our model evaluates the relative doses using the same input parameters as in the LGP, which are skull measurement data, shot location, weight, gamma-angle of the head frame, and helmet collimator size. For 29 single-shot cases, the discrepancy of dose at the focus point between the calculation and the LGP is found to be within -1% to 2%. For multi-shot cases, the value and the coordinate of the maximum dose point from the calculation agree within +/-7% and +/-3 mm with the LGP results. In general, the calculated doses agree with the LGP calculations within +/-10% for the off-center locations. Results of calculation with this method for the dimension and location of the 50% isodose line are in good agreement with results from Leksell GammaPlan. Therefore, this method can be served as a useful tool for secondary quality assurance of Gamma Knife treatment plans. PMID:12349920

Phaisangittisakul, Nakorn; Ma, Lijun

2002-09-01

190

The myth of mean dose as a surrogate for radiation risk?  

NASA Astrophysics Data System (ADS)

The current estimations of risk associated with medical imaging procedures rely on assessing the organ dose via direct measurements or simulation. Each organ dose is assumed to be homogeneous, a representative sample or mean of which is weighted by a corresponding tissue weighting factor provided by ICRP publication 103. The weighted values are summed to provide Effective Dose (ED), the most-widely accepted surrogate for population radiation risk. For individual risk estimation, one may employ Effective Risk (ER), which further incorporates gender- and age-specific risk factors. However, both the tissue-weighting factors (as used by ED) and the risk factors (as used by ER) were derived (mostly from the atomic bomb survivor data) under the assumption of a homogeneous dose distribution within each organ. That assumption is significantly violated in most medical imaging procedures. In chest CT, for example, superficial organs (eg, breasts) demonstrate a heterogeneous distribution while organs on the peripheries of the irradiation field (eg, liver) possess a nearly discontinuous dose profile. Projection radiography and mammography involve an even wider range of organ dose heterogeneity spanning up to two orders of magnitude. As such, mean dose or point measured dose values do not reflect the maximum energy deposited per unit volume of the organ, and therefore, effective dose or effective risk, as commonly computed, can misrepresent irradiation risk. In this paper, we report the magnitude of the dose heterogeneity in both CT and projection x-ray imaging, provide an assessment of its impact on irradiation risk, and explore an alternative model-based approach for risk estimation for imaging techniques involving heterogeneous organ dose distributions.

Samei, Ehsan; Li, Xiang; Chen, Baiyu; Reiman, Robert

2010-04-01

191

Sweeping Points  

Microsoft Academic Search

Given a set of points in the plane, and a sweep-line as a tool, what is best way to move the points to a target point using\\u000a a sequence of sweeps? In a sweep, the sweep-line is placed at a start position somewhere in the plane, then moved orthogonally\\u000a and continuously to another parallel end position, and then lifted from

Adrian Dumitrescu; Minghui Jiang

2011-01-01

192

Evaluation of brachytherapy lung implant dose distributions from photon-emitting sources due to tissue heterogeneities  

SciTech Connect

Purpose: Photon-emitting brachytherapy sources are used for permanent implantation to treat lung cancer. However, the current brachytherapy dose calculation formalism assumes a homogeneous water medium without considering the influence of radiation scatter or tissue heterogeneities. The purpose of this study was to determine the dosimetric effects of tissue heterogeneities for permanent lung brachytherapy. Methods: The MCNP5 v1.40 radiation transport code was used for Monte Carlo (MC) simulations. Point sources with energies of 0.02, 0.03, 0.05, 0.1, 0.2, and 0.4 MeV were simulated to cover the range of pertinent brachytherapy energies and to glean dosimetric trends independent of specific radionuclide emissions. Source positions from postimplant CT scans of five patient implants were used for source coordinates, with dose normalized to 200 Gy at the center of each implant. With the presence of fibrosis (around the implant), cortical bone, lung, and healthy tissues, dose distributions and {sub PTV}DVH were calculated using the MCNP *FMESH4 tally and the NIST mass-energy absorption coefficients. This process was repeated upon replacing all tissues with water. For all photon energies, 10{sup 9} histories were simulated to achieve statistical errors (k = 1) typically of 1%. Results: The mean PTV doses calculated using tissue heterogeneities for all five patients changed (compared to dose to water) by only a few percent over the examined photon energy range, as did PTV dose at the implant center. The {sub PTV}V{sub 100} values were 81.2%, 90.0% (as normalized), 94.3%, 93.9%, 92.7%, and 92.2% for 0.02, 0.03, 0.05, 0.1, 0.2, and 0.4 MeV source photons, respectively. Relative to water, the maximum bone doses were higher by factors of 3.7, 5.1, 5.2, 2.4, 1.2, and 1.0 The maximum lung doses were about 0.98, 0.94, 0.91, 0.94, 0.97, and 0.99. Relative to water, the maximum healthy tissue doses at the mediastinal position were higher by factors of 9.8, 2.2, 1.3, 1.1, 1.1, and 1.1. However, the maximum doses to these healthy tissues were only 3.1, 7.2, 11.3, 10.9, 9.0, and 8.1 Gy while maximum bone doses were 66, 177, 236, 106, 49, and 39 Gy, respectively. Similarly, maximum lung doses were 55, 66, 73, 74, 73, and 73 Gy, respectively. Conclusions: The current brachytherapy dose calculation formalism overestimates PTV dose and significantly underestimates doses to bone and healthy tissue. Further investigation using specific brachytherapy source models and patient-based CT datasets as MC input may indicate whether the observed trends can be generalized for low-energy lung brachytherapy dosimetry.

Yang Yun; Rivard, Mark J. [Tufts University School of Medicine, Boston, Massachusetts 02111 (United States)

2011-11-15

193

Tipping Points  

Microsoft Academic Search

A climate tipping point, at least as I have used the phrase, refers to a situation in which a changing climate forcing has reached a point such that little additional forcing (or global temperature change) is needed to cause large, relatively rapid, climate change. Present examples include potential loss of all Arctic sea ice and instability of the West Antarctic

J. Hansen

2007-01-01

194

Tipping Points  

NASA Astrophysics Data System (ADS)

A climate tipping point, at least as I have used the phrase, refers to a situation in which a changing climate forcing has reached a point such that little additional forcing (or global temperature change) is needed to cause large, relatively rapid, climate change. Present examples include potential loss of all Arctic sea ice and instability of the West Antarctic and Greenland ice sheets. Tipping points are characterized by ready feedbacks that amplify the effect of forcings. The notion that these may be runaway feedbacks is a misconception. However, present "unrealized" global warming, due to the climate system's thermal inertia, exacerbates the difficulty of avoiding global warming tipping points. I argue that prompt efforts to slow CO2 emissions and absolutely reduce non-CO2 forcings are both essential if we are to avoid tipping points that would be disastrous for humanity and creation, the planet as civilization knows it.

Hansen, J.

2007-12-01

195

Maximum Entropy Inverse Reinforcement Learning  

Microsoft Academic Search

Recent research has shown the benefit of framing problems of imitation learning as solutions to Markov Decision Prob- lems. This approach reduces learning to the problem of re- covering a utility function that makes the behavior induced by a near-optimal policy closely mimic demonstrated behav- ior. In this work, we develop a probabilistic approach based on the principle of maximum

Brian Ziebart; Andrew L. Maas; J. Andrew Bagnell; Anind K. Dey

2008-01-01

196

Dose calculations for external photon beams in radiotherapy  

Microsoft Academic Search

Dose calculation methods for photon beams are reviewed in the context of radiation therapy treatment planning. Following introductory summaries on photon beam characteristics and clinical requirements on dose calculations, calculation methods are described in order of increasing explicitness of particle transport. The simplest are dose ratio factorizations limited to point dose estimates useful for checking other more general, but also

Anders Ahnesj; Maria Mania Aspradakis

1999-01-01

197

Use of a realistic breathing lung phantom to evaluate dose delivery errors  

SciTech Connect

Purpose: To compare the effect of respiration-induced motion on delivered dose (the interplay effect) for different treatment techniques under realistic clinical conditions. Methods: A flexible resin tumor model was created using rapid prototyping techniques based on a computed tomography (CT) image of an actual tumor. Twenty micro-MOSFETs were inserted into the tumor model and the tumor model was inserted into an anthropomorphic breathing phantom. Phantom motion was programed using the motion trajectory of an actual patient. A four-dimensional CT image was obtained and several treatment plans were created using different treatment techniques and planning systems: Conformal (Eclipse), step-and-shoot intensity-modulated radiation therapy (IMRT) (Pinnacle), step-and-shoot IMRT (XiO), dynamic IMRT (Eclipse), complex dynamic IMRT (Eclipse), hybrid IMRT [60% conformal, 40% dynamic IMRT (Eclipse)], volume-modulated arc therapy (VMAT) [single-arc (Eclipse)], VMAT [double-arc (Eclipse)], and complex VMAT (Eclipse). The complex plans were created by artificially pushing the optimizer to give complex multileaf collimator sequences. Each IMRT field was irradiated five times and each VMAT field was irradiated ten times, with each irradiation starting at a random point in the respiratory cycle. The effect of fractionation was calculated by randomly summing the measured doses. The maximum deviation for each measurement point per fraction and the probability that 95% of the model tumor had dose deviations less than 2% and 5% were calculated as a function of the number of fractions. Tumor control probabilities for each treatment plan were calculated and compared. Results: After five fractions, measured dose deviations were less than 2% for more than 95% of measurement points within the tumor model for all plans, except the complex dynamic IMRT, step-and-shoot IMRT (XiO), complex VMAT, and single-arc VMAT plans. Reducing the dose rate of the complex IMRT plans from 600 to 200 MU/min reduced the dose deviations to less than 2%. Dose deviations were less than 5% after five fractions for all plans, except the complex single-arc VMAT plan. Conclusions: Rapid prototyping techniques can be used to create realistic tumor models. For most treatment techniques, the dose deviations averaged out after several fractions. Treatments with unusually complicated multileaf collimator sequences had larger dose deviations. For IMRT treat-ments, dose deviations can be reduced by reducing the dose rate. For VMAT treatments, using two arcs instead of one is effective for reducing dose deviations.

Court, Laurence E.; Seco, Joao; Lu Xingqi; Ebe, Kazuyu; Mayo, Charles; Ionascu, Dan; Winey, Brian; Giakoumakis, Nikos; Aristophanous, Michalis; Berbeco, Ross; Rottman, Joerg; Bogdanov, Madeleine; Schofield, Deborah; Lingos, Tania [Dana-Farber Cancer Institute and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115 (United States); Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114 (United States); Beth-Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02130 (United States); JA Jouetsu Hospital, Jouetsu 355-0063 (Japan); University of Massachusetts Memorial Medical Center, Worcester, Massachusetts 01655 (United States); William Beaumont Hospital, Royal Oak, Michigan 48073 (United States); Dana-Farber Cancer Institute and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115 (United States) and Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114 (United States); Dana-Farber Cancer Institute and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115 (United States)

2010-11-15

198

Solar maximum thermal surface assessment  

NASA Technical Reports Server (NTRS)

The inflight repair of the Solar Maximum Spacecraft provided the first opportunity to make actual measurements of thermal control surfaces after 4 years exposure in low Earth orbit. Defective hardware was replaced by astronauts and returned to Earth while protected from reentry damage in the Shuttle Payload bay. A preliminary thermal surface assessment was made soon after retrieval in support of Space Telescope and other current spacecraft programs. This included visual examination and measurement of Kapton and Teflon film to determine change in thermal radiative properties after 4 years exposure to solar radiation and reaction with atomic oxygen. Comparative measurements were made with a portable solar reflectometer used for inspection of spacecraft hardware. Post flight measurements and observations reveal significant surface changes that further confirm Kapton mass loss predictions made prior to Solar Maximum repair. Details of thermal surface application, measurements and experimental results are presented and discussed.

Rhoads, G. D.

1985-01-01

199

Maximum Sustainable Yield Lives On  

Microsoft Academic Search

I examined 142 papers published from 1977 through 1985 that used the concept of maximum sustainable yield (MSY). I classified them as to how MSY was used, year of publication, subject, and publication forum. The primary uses of MSY were in estimating long-term yield (28.9%), evaluating stock condition (28.2%), and analyzing policy (21.8%). The number of such publications declined significantly

Willard E. Barber

1988-01-01

200

BGIM : Maximum Likelihood Estimation Primer  

NSDL National Science Digital Library

Created by Shaun Purcell of the Social, Genetic and Development Pyschiatry Research Centre, this set of pages is an introduction to the maximum likelihood estimation. It discusses the likelihood and log-likelihood functions and the process of optimizing. The author breaks the page down in this way: introduction, model-fitting, MLE in practice, likelihood ratio test, MLE analysis of twin data and MLE analysis of linkage data. The author offers further reading for extra study of this statistical method.

Purcell, Shaun

2009-02-26

201

Dose responses for adaption to low doses of (60)Co gamma rays and (3)H beta particles in normal human fibroblasts.  

PubMed

The dose response for adaption to radiation at low doses was compared in normal human fibroblasts (AG1522) exposed to either (60)Co gamma rays or (3)H beta particles. Cells were grown in culture to confluence and exposed at either 37 degrees C or 0 degrees C to (3)H beta-particle or (60)Co gamma-ray adapting doses ranging from 0.1 mGy to 500 mGy. These cells, and unexposed control cells, were allowed to adapt during a fixed 3-h, 37 degrees C incubation prior to a 4-Gy challenge dose of (60)Co gamma rays. Adaption was assessed by measuring micronucleus frequency in cytokinesis-blocked, binucleate cells. No adaption was detected in cells exposed to (60)Co gamma radiation at 37 degrees C after a dose of 0.1 mGy given at a low dose rate or to 500 mGy given at a high dose rate. However, low-dose-rate exposure (1-3 mGy/min) to any dose between 1 and 500 mGy from either radiation, delivered at either temperature, caused cells to adapt and reduced the micronucleus frequency that resulted from the subsequent 4-Gy exposure. Within this dose range, the magnitude of the reduction was the same, regardless of the dose or radiation type. These results demonstrate that doses as low as (on average) about one track per cell (1 mGy) produce the same maximum adaptive response as do doses that deposit many tracks per cell, and that the two radiations were not different in this regard. Exposure at a temperature where metabolic processes, including DNA repair, were inactive (0 degrees C) did not alter the result, indicating that the adaptive response is not sensitive to changes in the accumulation of DNA damage within this range. The results also show that the RBE for low doses of tritium beta-particle radiation is 1, using adaption as the end point. PMID:12105988

Broome, E J; Brown, D L; Mitchel, R E J

2002-08-01

202

Aircraft as adaptive nonlinear system which must be in the adaptational maximum zone for safety  

SciTech Connect

Safety is a main problem in aircraft. We are considering this problem from the point of view related to existence of the adaptational maximum in complex developing systems. Safety space of aircraft parameters are determined. This space is transformed to different regimes of flight, when one engine malfunctions etc., are considered. Also it is shown that maximum safety is in adaptational maximum zone.

Ignative, M. [State Aerospace Instruments Academy, St. Petersburg (Russian Federation); Simatos, N. [Apollo Aerospace International, Daytona Beach, FL (United States); Sivasundaram, S. [Embry-Riddle Aeronautical Univ., Daytona Beach, FL (United States)

1994-12-31

203

HADOC: a computer code for calculation of external and inhalation doses from acute radionuclide releases  

SciTech Connect

The computer code HADOC (Hanford Acute Dose Calculations) is described and instructions for its use are presented. The code calculates external dose from air submersion and inhalation doses following acute radionuclide releases. Atmospheric dispersion is calculated using the Hanford model with options to determine maximum conditions. Building wake effects and terrain variation may also be considered. Doses are calculated using dose conversion factor supplied in a data library. Doses are reported for one and fifty year dose commitment periods for the maximum individual and the regional population (within 50 miles). The fractional contribution to dose by radionuclide and exposure mode are also printed if requested.

Strenge, D.L.; Peloquin, R.A.

1981-04-01

204

Dose-response relationship from longitudinal data with response-dependent dose modification using likelihood methods.  

PubMed

In some clinical trials or clinical practice, the therapeutic agent is administered repeatedly, and doses are adjusted in each patient based on repeatedly measured continuous responses, to maintain the response levels in a target range. Because a lower dose tends to be selected for patients with a better outcome, simple summarizations may wrongly show a better outcome for the lower dose, producing an incorrect dose-response relationship. In this study, we consider the dose-response relationship under these situations. We show that maximum-likelihood estimates are consistent without modeling the dose-modification mechanisms when the selection of the dose as a time-dependent covariate is based only on observed, but not on unobserved, responses, and measurements are generated based on administered doses. We confirmed this property by performing simulation studies under several dose-modification mechanisms. We examined an autoregressive linear mixed effects model. The model represents profiles approaching each patient's asymptote when identical doses are repeatedly administered. The model takes into account the previous dose history and provides a dose-response relationship of the asymptote as a summary measure. We also examined a linear mixed effects model assuming all responses are measured at steady state. In the simulation studies, the estimates of both the models were unbiased under the dose modification based on observed responses, but biased under the dose modification based on unobserved responses. In conclusion, the maximum-likelihood estimates of the dose-response relationship are consistent under the dose modification based only on observed responses. PMID:22641310

Funatogawa, Ikuko; Funatogawa, Takashi

2012-07-01

205

A modified tracking algorithm for maximum power tracking of solar array  

Microsoft Academic Search

Maximum power point tracking (MPPT) techniques are usually used for solar power applications. This paper discusses: (1) various connection methods between solar arrays and loads and (2) various maximum power point control methods and MPPT algorithms. In this paper, the solar array is treated as a current source instead of a voltage source. Analytical models are built for the solar

Chihchiang Hua; Jongrong Lin

2004-01-01

206

Maximum Flux Transition Paths of Conformational Change  

PubMed Central

Given two metastable states A and B of a biomolecular system, the problem is to calculate the likely paths of the transition from A to B. Such a calculation is more informative and more manageable if done for a reduced set of collective variables chosen so that paths cluster in collective variable space. The computational task becomes that of computing the “center” of such a cluster. A good way to define the center employs the concept of a committor, whose value at a point in collective variable space is the probability that a trajectory at that point will reach B before A. The committor “foliates” the transition region into a set of isocommittors. The maximum flux transition path is defined as a path that crosses each isocommittor at a point which (locally) has the highest crossing rate of distinct reactive trajectories. This path is based on the same principle as the minimum resistance path of Berkowitz et al (1983), but it has two advantages: (i) the path is invariant with respect to a change of coordinates in collective variable space and (ii) the differential equations that define the path are simpler. It is argued that such a path is nearer to an ideal path than others that have been proposed with the possible exception of the finite-temperature string method path. To make the calculation tractable, three approximations are introduced, yielding a path that is the solution of a nonsingular two-point boundary-value problem. For such a problem, one can construct a simple and robust algorithm. One such algorithm and its performance is discussed. PMID:20890401

Zhao, Ruijun; Shen, Juanfang; Skeel, Robert D.

2010-01-01

207

An overview of the solar maximum mission  

NASA Technical Reports Server (NTRS)

The Solar Maximum Mission (SMM), devoted to the study of active solar phenomena is expected to be launched in February 1980 and operate throughout the peak of the current maximum of solar activity. The SMM observatory consists of two main sections: the instrument module which houses the solar payload instruments and the Fine Pointing Sun Sensor System, and the Multimission Modular Spacecraft (MMS) which carries the spacecraft subsystem modules. The entire observatory is 4m long and 2.3m in diameter. The SMM will carry a payload of six instruments specifically selected to study the short wavelength and coronal manifestations of flares. These include: gamma ray spectrometer, hard X-ray burst spectrometer, hard-X-ray imaging spectrometer, soft X-ray polychromator, UV spectrometer and polarimeter, coronagraph/polarimeter and solar constant monitoring package which will measure the total solar irradiance to an accuracy of 0.1 percent. Specific scientific objectives will include: chromospheric evaporation, thermalization, electron acceleration and flare build-up. Complementary studies will be made as part of an SMM Guest Investigator Program. The SMM observation program will be operated on a 24 hour cycle.

Chipman, E. C.; Frost, K. J.

1980-01-01

208

Maximum likelihood techniques in QELS  

NASA Technical Reports Server (NTRS)

A framework for the analysis of Quasi Elastic Light Scattering (QELS) experiments designed to be used in microgravity environment is derived. Example calculations of the type to be used to design the QELS system are given. The framework for the analysis is based on the concepts of parameter estimation typified by Maximum Likelihood Estimation methods. These methods not only serve as the template for parameter estimation algorithms, but can also be used for optimal design of the experiments. Optimal design of experiments is facilitated by the fact that these methods not only give procedures for parameter estimation, but also estimates of the errors associated with the parameter estimation.

Edwards, Robert V.

1989-01-01

209

Maximum life spur gear design  

NASA Technical Reports Server (NTRS)

Optimization procedures allow one to design a spur gear reduction for maximum life and other end use criteria. A modified feasible directions search algorithm permits a wide variety of inequality constraints and exact design requirements to be met with low sensitivity to initial guess values. The optimization algorithm is described, and the models for gear life and performance are presented. The algorithm is compact and has been programmed for execution on a desk top computer. Two examples are presented to illustrate the method and its application.

Savage, M.; Mackulin, B. J.; Coe, H. H.; Coy, J. J.

1991-01-01

210

Maximum-likelihood reconstruction for single-photon emission computedtomography  

Microsoft Academic Search

A mathematical model is formulated for a gamma camera used to observe single-photon emissions from multiple view angles. The model accounts for the statistics of radioactive decays, nonuniform attenuation, and a depth-dependent point-spread function. The maximum-likelihood method of statistics is used with the model to derive an algorithm for estimating the distribution of radioactivity.

Michael I. Miller; T. R. Miller; D. L. Snyder

1985-01-01

211

A revision of the ggr-evaluation concept for the comparison of dose distributions  

NASA Astrophysics Data System (ADS)

A method for the quantitative four-dimensional (4D) evaluation of discrete dose data based on gradient-dependent local acceptance thresholds is presented. The method takes into account the local dose gradients of a reference distribution for critical appraisal of misalignment and collimation errors. These contribute to the maximum tolerable dose error at each evaluation point to which the local dose differences between comparison and reference data are compared. As shown, the presented concept is analogous to the ggr-concept of Low et al (1998a Med. Phys. 25 656-61) if extended to (3+1) dimensions. The pointwise dose comparisons of the reformulated concept are easier to perform and speed up the evaluation process considerably, especially for fine-grid evaluations of 3D dose distributions. The occurrences of false negative indications due to the discrete nature of the data are reduced with the method. The presented method was applied to film-measured, clinical data and compared with ggr-evaluations. 4D and 3D evaluations were performed. Comparisons prove that 4D evaluations have to be given priority, especially if complex treatment situations are verified, e.g., non-coplanar beam configurations.

Bakai, Annemarie; Alber, Markus; Nüsslin, Fridtjof

2003-11-01

212

A revision of the gamma-evaluation concept for the comparison of dose distributions.  

PubMed

A method for the quantitative four-dimensional (4D) evaluation of discrete dose data based on gradient-dependent local acceptance thresholds is presented. The method takes into account the local dose gradients of a reference distribution for critical appraisal of misalignment and collimation errors. These contribute to the maximum tolerable dose error at each evaluation point to which the local dose differences between comparison and reference data are compared. As shown, the presented concept is analogous to the gamma-concept of Low et al (1998a Med. Phys. 25 656-61) if extended to (3+1) dimensions. The pointwise dose comparisons of the reformulated concept are easier to perform and speed up the evaluation process considerably, especially for fine-grid evaluations of 3D dose distributions. The occurrences of false negative indications due to the discrete nature of the data are reduced with the method. The presented method was applied to film-measured, clinical data and compared with gamma-evaluations. 4D and 3D evaluations were performed. Comparisons prove that 4D evaluations have to be given priority, especially if complex treatment situations are verified, e.g., non-coplanar beam configurations. PMID:14653561

Bakai, Annemarie; Alber, Markus; Nüsslin, Fridtjof

2003-11-01

213

Curie Point  

NSDL National Science Digital Library

In this activity best suited as a demonstration, learners observe that when a piece of iron gets too hot, it loses its ability to be magnetized. The temperature at which this occurs is known as the Curie Point. This simple set-up involving a lantern battery and Tinkertoys⢠demonstrates this phenomenon. Adult supervision required, as the wire will get hot in this activity.

Exploratorium, The

2012-01-30

214

Dew Point  

NSDL National Science Digital Library

Determine the dew point temperature for your classroom through a hands-on experiment. Use humidity and temperature probes to investigate the temperature at which it would rain in your classroom! Learn about water density and the conditions necessary to produce fog or rain.

Consortium, The C.

2011-12-13

215

A Comprehensive Analysis of Cardiac Dose in Balloon-Based High-Dose-Rate Brachytherapy for Left-Sided Breast Cancer  

SciTech Connect

Purpose: To investigate radiation dose to the heart in 60 patients with left-sided breast cancer who were treated with balloon-based high-dose-rate brachytherapy using MammoSite or Contura applicators. Methods and Materials: We studied 60 consecutive women with breast cancer who were treated with 34 Gy in 10 twice-daily fractions using MammoSite (n = 37) or Contura (n = 23) applicators. The whole heart and the left and right ventricles were retrospectively delineated, and dose-volume histograms were analyzed. Multiple dosimetrics were reported, such as mean dose (D{sub mean}); relative volume receiving 1.7, 5, 10, and 20 Gy (V1.7, V5, V10, and V20, respectively); dose to 1 cc (D{sub 1cc}); and maximum point dose (D{sub max}). Biologic metrics, biologically effective dose and generalized equivalent uniform dose were computed. The impact of lumpectomy cavity location on cardiac dose was investigated. Results: The average {+-} standard deviation of D{sub mean} was 2.45 {+-} 0.94 Gy (range, 0.56-4.68) and 3.29 {+-} 1.28 Gy (range, 0.77-6.35) for the heart and the ventricles, respectively. The average whole heart V5 and V10 values were 10.2% and 1.3%, respectively, and the heart D{sub max} was >20 Gy in 7 of 60 (11.7%) patients and >25 Gy in 3 of 60 (5%) patients. No cardiac tissue received {>=}30 Gy. The V1.7, V5, V10, V20, and D{sub mean} values were all higher for the ventricles than for the whole heart. For balloons located in the upper inner quadrant of the breast, the average whole heart D{sub mean} was highest. The D{sub mean}, biologically effective dose, and generalized equivalent uniform dose values for heart and ventricles decreased with increasing minimal distance from the surface of the balloon. Conclusions: On the basis of these comprehensive cardiac dosimetric data, we recommend that cardiac dose be routinely reported and kept as low as possible in balloon-based high-dose-rate brachytherapy treatment planning for patients with left-sided breast cancer so the correlation with future cardiac toxicity data can be investigated.

Valakh, Vladimir, E-mail: vladimir@valakh.com [Department of Radiation Oncology, Allegheny General Hospital, Pittsburgh, PA (United States); Kim, Yongbok; Werts, E. Day; Trombetta, Mark G. [Department of Radiation Oncology, Allegheny General Hospital, Pittsburgh, PA (United States); Drexel University College of Medicine, Allegheny Campus, Pittsburgh, PA (United States)

2012-04-01

216

Hermit Points on a Box  

ERIC Educational Resources Information Center

Suppose that we are given a rectangular box in 3-space. Given any two points on the surface of this box, we can define the surface distance between them to be the length of the shortest path between them on the surface of the box. This paper determines the pairs of points of maximum surface distance for all boxes. It is often the case that these…

Hess, Richard; Grinstead, Charles; Grindstead, Marshall; Bergstrand, Deborah

2008-01-01

217

Neutron capture therapy: a comparison between dose enhancement of various agents, nanoparticles and chemotherapy drugs.  

PubMed

The aim of this study is to compare dose enhancement of various agents, nanoparticles and chemotherapy drugs for neutron capture therapy. A (252)Cf source was simulated to obtain its dosimetric parameters, including air kerma strength, dose rate constant, radial dose function and total dose rates. These results were compared with previously published data. Using (252)Cf as a neutron source, the in-tumour dose enhancements in the presence of atomic (10)B, (157)Gd and (33)S agents; (10)B, (157)Gd, (33)S nanoparticles; and Bortezomib and Amifostine chemotherapy drugs were calculated and compared in neutron capture therapy. Monte Carlo code MCNPX was used for simulation of the (252)Cf source, a soft tissue phantom, and a tumour containing each capture agent. Dose enhancement for 100, 200 and 500 ppm of the mentioned media was calculated. Calculated dosimetric parameters of the (252)Cf source were in agreement with previously published values. In comparison to other agents, maximum dose enhancement factor was obtained for 500 ppm of atomic (10)B agent and (10)B nanoparticles, equal to 1.06 and 1.08, respectively. Additionally, Bortezomib showed a considerable dose enhancement level. From a dose enhancement point of view, media containing (10)B are the best agents in neutron capture therapy. Bortezomib is a chemotherapy drug containing boron and can be proposed as an agent in boron neutron capture therapy. However, it should be noted that other physical, chemical and medical criteria should be considered in comparing the mentioned agents before their clinical use in neutron capture therapy. PMID:24961208

Khosroabadi, Mohsen; Ghorbani, Mahdi; Rahmani, Faezeh; Knaup, Courtney

2014-09-01

218

System for memorizing maximum values  

NASA Astrophysics Data System (ADS)

The invention discloses a system capable of memorizing maximum sensed values. The system includes conditioning circuitry which receives the analog output signal from a sensor transducer. The conditioning circuitry rectifies and filters the analog signal and provides an input signal to a digital driver, which may be either linear or logarithmic. The driver converts the analog signal to discrete digital values, which in turn triggers an output signal on one of a plurality of driver output lines n. The particular output lines selected is dependent on the converted digital value. A microfuse memory device connects across the driver output lines, with n segments. Each segment is associated with one driver output line, and includes a microfuse that is blown when a signal appears on the associated driver output line.

Bozeman, Richard J., Jr.

1992-08-01

219

Dynamically accumulated dose and 4D accumulated dose for moving tumors  

SciTech Connect

Purpose: The purpose of this work was to investigate the relationship between dynamically accumulated dose (dynamic dose) and 4D accumulated dose (4D dose) for irradiation of moving tumors, and to quantify the dose uncertainty induced by tumor motion. Methods: The authors established that regardless of treatment modality and delivery properties, the dynamic dose will converge to the 4D dose, instead of the 3D static dose, after multiple deliveries. The bounds of dynamic dose, or the maximum estimation error using 4D or static dose, were established for the 4D and static doses, respectively. Numerical simulations were performed (1) to prove the principle that for each phase, after multiple deliveries, the average number of deliveries for any given time converges to the total number of fractions (K) over the number of phases (N); (2) to investigate the dose difference between the 4D and dynamic doses as a function of the number of deliveries for deliveries of a 'pulsed beam'; and (3) to investigate the dose difference between 4D dose and dynamic doses as a function of delivery time for deliveries of a 'continuous beam.' A Poisson model was developed to estimate the mean dose error as a function of number of deliveries or delivered time for both pulsed beam and continuous beam. Results: The numerical simulations confirmed that the number of deliveries for each phase converges to K/N, assuming a random starting phase. Simulations for the pulsed beam and continuous beam also suggested that the dose error is a strong function of the number of deliveries and/or total deliver time and could be a function of the breathing cycle, depending on the mode of delivery. The Poisson model agrees well with the simulation. Conclusions: Dynamically accumulated dose will converge to the 4D accumulated dose after multiple deliveries, regardless of treatment modality. Bounds of the dynamic dose could be determined using quantities derived from 4D doses, and the mean dose difference between the dynamic dose and 4D dose as a function of number of deliveries and/or total deliver time was also established.

Li Heng; Li Yupeng; Zhang Xiaodong; Li Xiaoqiang; Liu Wei; Gillin, Michael T.; Zhu, X. Ronald [Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States)

2012-12-15

220

Impact of dose hot spots on spinal cord tolerance following stereotactic body radiotherapy: a generalized biological effective dose analysis.  

PubMed

The purpose of this study was to investigate the effects of high-dose inhomogeneous irradiation to small volumes of spinal cord with a new generalized biological effective dose (gBED) analysis for spine stereotactic body radiotherapy (SBRT). The gBED was applied to spinal cord dosimetric data (contoured per the thecal sac) at specified volumes for a cohort of five patients with radiation-induced myelopathy (RM) and compared to nineteen patients without RM post-SBRT. The spinal cord gBED was calculated and normalized to a conventional 2-Gy equivalent dose fraction scheme (?/? = 2 Gy for late toxicity). Differences between the conventional BED and those gBED calculations by accounting for small-volume dosing within the spinal cord was observed. Statistically significant differences in the mean gBED between the RM group and the non-RM group was observed both at the maximum point volume (gBED of 66 Gy vs. 37 Gy (p = 0.01), respectively) and at the 0.1 cm(3) volume (gBED of 53 Gy vs. 28 Gy (p = 0.01), respectively). No significant difference at the 0.1 cm(3) volume was observed based on the mean BED comparisons. No significant differences were observed at the larger 1 cm(3), 2 cm(3) or 5 cm(3) volumes for either BED or gBED comparisons. We conclude that differences in dose hot spots characteristics within small inhomogenously irradiated volumes of spinal cord can affect spinal cord tolerance following SBRT treatments. PMID:22181329

Sahgal, A; Ma, L; Fowler, J; Weinberg, V; Gibbs, I; Gerszten, P C; Ryu, S; Soltys, S; Chang, E; Wong, C S; Larson, D A

2012-02-01

221

Technical basis for dose reconstruction  

SciTech Connect

The purpose of this paper is to consider two general topics: technical considerations of why dose-reconstruction studies should or should not be performed and methods of dose reconstruction. The first topic is of general and growing interest as the number of dose-reconstruction studies increases, and one asks the question whether it is necessary to perform a dose reconstruction for virtually every site at which, for example, the Department of Energy (DOE) has operated a nuclear-related facility. And there is the broader question of how one might logically draw the line at performing or not performing dose-reconstruction (radiological and chemical) studies for virtually every industrial complex in the entire country. The second question is also of general interest. There is no single correct way to perform a dose-reconstruction study, and it is important not to follow blindly a single method to the point that cheaper, faster, more accurate, and more transparent methods might not be developed and applied.

Anspaugh, L.R.

1996-01-31

222

2011 Radioactive Materials Usage Survey for Unmonitored Point Sources  

SciTech Connect

This report provides the results of the 2011 Radioactive Materials Usage Survey for Unmonitored Point Sources (RMUS), which was updated by the Environmental Protection (ENV) Division's Environmental Stewardship (ES) at Los Alamos National Laboratory (LANL). ES classifies LANL emission sources into one of four Tiers, based on the potential effective dose equivalent (PEDE) calculated for each point source. Detailed descriptions of these tiers are provided in Section 3. The usage survey is conducted annually; in odd-numbered years the survey addresses all monitored and unmonitored point sources and in even-numbered years it addresses all Tier III and various selected other sources. This graded approach was designed to ensure that the appropriate emphasis is placed on point sources that have higher potential emissions to the environment. For calendar year (CY) 2011, ES has divided the usage survey into two distinct reports, one covering the monitored point sources (to be completed later this year) and this report covering all unmonitored point sources. This usage survey includes the following release points: (1) all unmonitored sources identified in the 2010 usage survey, (2) any new release points identified through the new project review (NPR) process, and (3) other release points as designated by the Rad-NESHAP Team Leader. Data for all unmonitored point sources at LANL is stored in the survey files at ES. LANL uses this survey data to help demonstrate compliance with Clean Air Act radioactive air emissions regulations (40 CFR 61, Subpart H). The remainder of this introduction provides a brief description of the information contained in each section. Section 2 of this report describes the methods that were employed for gathering usage survey data and for calculating usage, emissions, and dose for these point sources. It also references the appropriate ES procedures for further information. Section 3 describes the RMUS and explains how the survey results are organized. The RMUS Interview Form with the attached RMUS Process Form(s) provides the radioactive materials survey data by technical area (TA) and building number. The survey data for each release point includes information such as: exhaust stack identification number, room number, radioactive material source type (i.e., potential source or future potential source of air emissions), radionuclide, usage (in curies) and usage basis, physical state (gas, liquid, particulate, solid, or custom), release fraction (from Appendix D to 40 CFR 61, Subpart H), and process descriptions. In addition, the interview form also calculates emissions (in curies), lists mrem/Ci factors, calculates PEDEs, and states the location of the critical receptor for that release point. [The critical receptor is the maximum exposed off-site member of the public, specific to each individual facility.] Each of these data fields is described in this section. The Tier classification of release points, which was first introduced with the 1999 usage survey, is also described in detail in this section. Section 4 includes a brief discussion of the dose estimate methodology, and includes a discussion of several release points of particular interest in the CY 2011 usage survey report. It also includes a table of the calculated PEDEs for each release point at its critical receptor. Section 5 describes ES's approach to Quality Assurance (QA) for the usage survey. Satisfactory completion of the survey requires that team members responsible for Rad-NESHAP (National Emissions Standard for Hazardous Air Pollutants) compliance accurately collect and process several types of information, including radioactive materials usage data, process information, and supporting information. They must also perform and document the QA reviews outlined in Section 5.2.6 (Process Verification and Peer Review) of ES-RN, 'Quality Assurance Project Plan for the Rad-NESHAP Compliance Project' to verify that all information is complete and correct.

Sturgeon, Richard W. [Los Alamos National Laboratory

2012-06-27

223

Fast maximum entropy Doppler mapping  

E-print Network

A numerical code is described for constructing Doppler maps from the orbital variation of line profiles of (mass transfering) binaries. It uses an algorithm related to Richardson-Lucy iteration, and is much faster than the standard algorithm used for ME problems. The method has been tested on data of cataclysmic variables (including WZ Sge and SS Cyg), producing maps of up to 300X300 points. It includes an IDL-based set of routines for manipulating and plotting the input and output data, and can be downloaded from http://www.mpa-garching.mpg.de/~henk

H. C. Spruit

1998-06-10

224

Radiation Doses in Perspective  

MedlinePLUS

... Health Effects Ionizing & Non-Ionizing Radiation Understanding Radiation: Radiation Doses in Perspective Health Effects Main Page Exposure ... Sources Doses from Common Radiation Sources Average U.S. Radiation Doses and Sources All of us are exposed ...

225

Radiation Dose Chart  

NSDL National Science Digital Library

This is an illustration of the ionizing radiation dose a person can absorb from various sources. It provides a visual comparison of doses ranging from 0.1 microsieverts (from eating a banana) to a fatal dose of 8 sieverts.

Munroe, Randall

226

Dose and dose rate effectiveness of space radiation.  

PubMed

Dose and dose rate effectiveness factors (DDREF), in conjunction with other weighting factors, are commonly used to scale atomic bomb survivor data in order to establish limits for occupational radiation exposure, including radiation exposure in space. We use some well-known facts about the microscopic pattern of energy deposition of high-energy heavy ions, and about the dose rate dependence of chemical reactions initiated by radiation, to show that DDREF are likely to vary significantly as a function of particle type and energy, cell, tissue, and organ type, and biological end point. As a consequence, we argue that validation of DDREF by conventional methods, e.g. irradiating animal colonies and compiling statistics of cancer mortality, is not appropriate. However, the use of approaches derived from information theory and thermodynamics is a very wide field, and the present work can only be understood as a contribution to an ongoing discussion. PMID:17169950

Schimmerling, W; Cucinotta, F A

2006-01-01

227

Maximum entropy production in daisyworld  

NASA Astrophysics Data System (ADS)

Daisyworld was first introduced in 1983 by Watson and Lovelock as a model that illustrates how life can influence a planet's climate. These models typically involve modeling a planetary surface on which black and white daisies can grow thus influencing the local surface albedo and therefore also the temperature distribution. Since then, variations of daisyworld have been applied to study problems ranging from ecological systems to global climate. Much of the interest in daisyworld models is due to the fact that they enable one to study self-regulating systems. These models are nonlinear, and as such they exhibit sensitive dependence on initial conditions, and depending on the specifics of the model they can also exhibit feedback loops, oscillations, and chaotic behavior. Many daisyworld models are thermodynamic in nature in that they rely on heat flux and temperature gradients. However, what is not well-known is whether, or even why, a daisyworld model might settle into a maximum entropy production (MEP) state. With the aim to better understand these systems, this paper will discuss what is known about the role of MEP in daisyworld models.

Maunu, Haley A.; Knuth, Kevin H.

2012-05-01

228

Focused Fields of given Power with Maximum Electric Field Components  

E-print Network

Closed formulas are derived for the field in the focal region of a diffraction limited lens, such that the electric field component in a given direction at the focal point is larger than that of all other focused fields with the same power in the entrance pupil of the lens. Furthermore, closed formulas are derived for the corresponding optimum field distribution in the lens pupil. Focused fields with maximum longitudinal or maximum transverse are considered in detail. The latter field is similar, but not identical, to the focused linearly polarized plane wave.

Pereira, H P Urbach S F

2008-01-01

229

The impact of dose calculation algorithms on partial and whole breast radiation treatment plans  

PubMed Central

Background This paper compares the calculated dose to target and normal tissues when using pencil beam (PBC), superposition/convolution (AAA) and Monte Carlo (MC) algorithms for whole breast (WBI) and accelerated partial breast irradiation (APBI) treatment plans. Methods Plans for 10 patients who met all dosimetry constraints on a prospective APBI protocol when using PBC calculations were recomputed with AAA and MC, keeping the monitor units and beam angles fixed. Similar calculations were performed for WBI plans on the same patients. Doses to target and normal tissue volumes were tested for significance using the paired Student's t-test. Results For WBI plans the average dose to target volumes when using PBC calculations was not significantly different than AAA calculations, the average PBC dose to the ipsilateral breast was 10.5% higher than the AAA calculations and the average MC dose to the ipsilateral breast was 11.8% lower than the PBC calculations. For ABPI plans there were no differences in dose to the planning target volume, ipsilateral breast, heart, ipsilateral lung, or contra-lateral lung. Although not significant, the maximum PBC dose to the contra-lateral breast was 1.9% higher than AAA and the PBC dose to the clinical target volume was 2.1% higher than AAA. When WBI technique is switched to APBI, there was significant reduction in dose to the ipsilateral breast when using PBC, a significant reduction in dose to the ipsilateral lung when using AAA, and a significant reduction in dose to the ipsilateral breast and lung and contra-lateral lung when using MC. Conclusions There is very good agreement between PBC, AAA and MC for all target and most normal tissues when treating with APBI and WBI and most of the differences in doses to target and normal tissues are not clinically significant. However, a commonly used dosimetry constraint, as recommended by the ASTRO consensus document for APBI, that no point in the contra-lateral breast volume should receive >3% of the prescribed dose needs to be relaxed to >5%. PMID:21162739

2010-01-01

230

Radiological Dose Assessment 8 2003 SITE ENVIRONMENTAL REPORT8-1  

E-print Network

Radiological Dose Assessment 8 2003 SITE ENVIRONMENTAL REPORT8-1 Brookhaven National Laboratory routinely assesses its operations to ensure that any potential radiological dose to the public, BNL workers radiological dose to the public is calculated as the maximum dose to a hypothetical Maximally Exposed

Homes, Christopher C.

231

Quick Organ Diagnosis and Treatment according to Bi-Digital O-Ring Test Measurements of Current Maximum Potential Relative Function, Relative Amount of Telomere and Acetylcholine, and Circulatory Disturbance on Organ Representation Points: Comparison with Palpation Diagnosis of Pressure Pain  

Microsoft Academic Search

The study aimed to find the factors that could be measured with the Bi-Digital O-Ring Test on an internal organ representation point (ORP) that would integrate with the diagnosis of palpable reflexive pressure pain (PP) on the ORP and on other related locations on the body often used in some acupuncture (AP) systems. The basic BDORT of function and the

Richard Malter; Dip Shiatsu; Cert Dry Needling

232

Analytical representation for Varian EDW factors at off-center points  

SciTech Connect

The purpose of this study is to describe and evaluate a new analytical model for Varian enhanced dynamic wedge factors at off-center points. The new model was verified by comparing measured and calculated wedge factors for the standard set of wedge angles (i.e., 15 deg., 30 deg., 45 deg. and 60 deg.), different symmetric and asymmetric fields, and two different photon energies. The maximum difference between calculated and measured wedge factors is less than 2%. The average absolute difference is within 1%. The obtained results indicate that the suggested model can be useful for independent dose calculation with enhanced dynamic wedges.

Kuperman, Vadim Y. [James A. Haley Veterans Hospital, Tampa, Florida 33612 (United States)

2005-05-01

233

Maximum entropy principal for transportation  

SciTech Connect

In this work we deal with modeling of the transportation phenomenon for use in the transportation planning process and policy-impact studies. The model developed is based on the dependence concept, i.e., the notion that the probability of a trip starting at origin i is dependent on the probability of a trip ending at destination j given that the factors (such as travel time, cost, etc.) which affect travel between origin i and destination j assume some specific values. The derivation of the solution of the model employs the maximum entropy principle combining a priori multinomial distribution with a trip utility concept. This model is utilized to forecast trip distributions under a variety of policy changes and scenarios. The dependence coefficients are obtained from a regression equation where the functional form is derived based on conditional probability and perception of factors from experimental psychology. The dependence coefficients encode all the information that was previously encoded in the form of constraints. In addition, the dependence coefficients encode information that cannot be expressed in the form of constraints for practical reasons, namely, computational tractability. The equivalence between the standard formulation (i.e., objective function with constraints) and the dependence formulation (i.e., without constraints) is demonstrated. The parameters of the dependence-based trip-distribution model are estimated, and the model is also validated using commercial air travel data in the U.S. In addition, policy impact analyses (such as allowance of supersonic flights inside the U.S. and user surcharge at noise-impacted airports) on air travel are performed.

Bilich, F. [University of Brasilia (Brazil); Da Silva, R. [National Research Council (Brazil)

2008-11-06

234

Life-Stage-, Sex-, and Dose-Dependent Dietary Toxicokinetics and Relationship to Toxicity of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Rats: Implications for Toxicity Test Dose Selection, Design, and Interpretation  

PubMed Central

Life-stage-dependent toxicity and dose-dependent toxicokinetics (TK) were evaluated in Sprague Dawley rats following dietary exposure to 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D renal clearance is impacted by dose-dependent saturation of the renal organic anion transporter; thus, this study focused on identifying inflection points of onset of dietary nonlinear TK to inform dose selection decisions for toxicity studies. Male and female rats were fed 2,4-D-fortified diets at doses to 1600 ppm for 4-weeks premating, <2 weeks during mating, and to test day (TD) 71 to parental (P1) males and to P1 females through gestation/lactation to TD 96. F1 offspring were exposed via milk with continuing diet exposure until postnatal day (PND) 35. As assessed by plasma area under the curve for the time-course plasma concentration, nonlinear TK was observed ?1200 ppm (63mg/kg/day) for P1 males and between 200 and 400 ppm (14–27mg/kg/day) for P1 females. Dam milk and pup plasma levels were higher on lactation day (LD) 14 than LD 4. Relative to P1 adults, 2,4-D levels were higher in dams during late gestation/lactation and postweaning pups (PND 21–35) and coincided with elevated intake of diet/kg body weight. Using conventional maximum tolerated dose (MTD) criteria based on body weight changes for dose selection would have resulted in excessive top doses approximately 2-fold higher than those identified incorporating critical TK data. These data indicate that demonstration of nonlinear TK, if present at dose levels substantially above real-world human exposures, is a key dose selection consideration for improving the human relevance of toxicity studies compared with studies employing conventional MTD dose selection strategies. PMID:24105888

Marty, Mary S.

2013-01-01

235

MILDOS - A Computer Program for Calculating Environmental Radiation Doses from Uranium Recovery Operations  

SciTech Connect

The MILDOS Computer Code estimates impacts from radioactive emissions from uranium milling facilities. These impacts are presented as dose commitments to individuals and the regional population within an 80 km radius of the facility. Only airborne releases of radioactive materials are considered: releases to surface water and to groundwater are not addressed in MILDOS. This code is multi-purposed and can be used to evaluate population doses for NEPA assessments, maximum individual doses for predictive 40 CFR 190 compliance evaluations, or maximum offsite air concentrations for predictive evaluations of 10 CFR 20 compliance. Emissions of radioactive materials from fixed point source locations and from area sources are modeled using a sector-averaged Gaussian plume dispersion model, which utilizes user-provided wind frequency data. Mechanisms such as deposition of particulates, resuspension. radioactive decay and ingrowth of daughter radionuclides are included in the transport model. Annual average air concentrations are computed, from which subsequent impacts to humans through various pathways are computed. Ground surface concentrations are estimated from deposition buildup and ingrowth of radioactive daughters. The surface concentrations are modified by radioactive decay, weathering and other environmental processes. The MILDOS Computer Code allows the user to vary the emission sources as a step function of time by adjustinq the emission rates. which includes shutting them off completely. Thus the results of a computer run can be made to reflect changing processes throughout the facility's operational lifetime. The pathways considered for individual dose commitments and for population impacts are: • Inhalation • External exposure from ground concentrations • External exposure from cloud immersion • Ingestioo of vegetables • Ingestion of meat • Ingestion of milk • Dose commitments are calculated using dose conversion factors, which are ultimately based on recommendations of the International Commission on Radiological Protection (ICRP). These factors are fixed internally in the code, and are not part of the input option. Dose commitments which are available from the code are as follows: • Individual dose commitments for use in predictive 40 CFR 190 compliance evaluations (Radon and short-lived daughters are excluded) • Total individual dose commitments (impacts from all available radionuclides are considered) • Annual population dose commitments (regional, extraregional, total and cummulative). This model is primarily designed for uranium mill facilities, and should not be used for operations with different radionuclides or processes.

Strange, D. L.; Bander, T. J.

1981-04-01

236

14 CFR 1261.102 - Maximum amount.  

Code of Federal Regulations, 2010 CFR

... 2010-01-01 false Maximum amount. 1261.102 Section 1261.102 Aeronautics and Space NATIONAL AERONAUTICS AND... Employees' Personal Property Claims § 1261.102 Maximum amount. From October 1, 1982,...

2010-01-01

237

''Natural'' volume--dose histogram for brachytherapy  

SciTech Connect

The most useful formulation of the volume--dose histogram for brachytherapy is one which suppresses inverse square law effects while preserving proportionality between volume and the area under the curve. These objectives are met by plotting the distribution of volume per unit -3/2 power of dose rate versus the -3/2 power of dose rate; such a distribution is constant for a single point source. Adding sources results in the formation of a peak, which provides a graphical indication of dose rate uniformity. Evaluation of other peak parameters such as width, position, and contained volume, in relation to treatment dose rate, permits a quantitative and clinically relevant volume--dose assessment of interstitial implants.

Anderson, L.L.

1986-11-01

238

HYDROMETEOROLOGICAL REPORT NO. 39 PROBABLE MAXIMUM PRECIPITATION"  

E-print Network

HYDROMETEOROLOGICAL REPORT NO. 39 PROBABLE MAXIMUM PRECIPITATION" IN THE HAWAllAN ISLANDS LOAN COPY (Nos. 6-22 Numbered Retroactively) *No: 1. Maximum possible precipitation over the Ompompanoos~c Basin above Union Villag~, Vt. 1943. *No. 2. Maximum possible precipitation over'the Ohio River-Basin above

239

Maximum Urban Heat Island Intensity in Seoul  

Microsoft Academic Search

The maximum urban heat island (UHI) intensity in Seoul, Korea, is investigated using data measured at two meteorological observatories (an urban site and a rural site) during the period of 1973-96. The average maximum UHI is weakest in summer and is strong in autumn and winter. Similar to previous studies for other cities, the maximum UHI intensity is more frequently

Yeon-Hee Kim; Jong-Jin Baik

2002-01-01

240

Precise Asymptotics for a Random Walker's Maximum  

E-print Network

We consider a discrete time random walk in one dimension. At each time step the walker jumps by a random distance, independent from step to step, drawn from an arbitrary symmetric density function. We show that the expected positive maximum E[M_n] of the walk up to n steps behaves asymptotically for large n as, E[M_n]/\\sigma=\\sqrt{2n/\\pi}+ \\gamma +O(n^{-1/2}), where \\sigma^2 is the variance of the step lengths. While the leading \\sqrt{n} behavior is universal and easy to derive, the leading correction term turns out to be a nontrivial constant \\gamma. For the special case of uniform distribution over [-1,1], Coffmann et. al. recently computed \\gamma=-0.516068...by exactly enumerating a lengthy double series. Here we present a closed exact formula for \\gamma valid for arbitrary symmetric distributions. We also demonstrate how \\gamma appears in the thermodynamic limit as the leading behavior of the difference variable E[M_n]-E[|x_n|] where x_n is the position of the walker after n steps. An application of these results to the equilibrium thermodynamics of a Rouse polymer chain is pointed out. We also generalize our results to L\\'evy walks.

Alain Comtet; Satya N. Majumdar

2005-06-08

241

Propane spectral resolution enhancement by the maximum entropy method  

NASA Technical Reports Server (NTRS)

The Burg algorithm for maximum entropy power spectral density estimation is applied to a time series of data obtained from a Michelson interferometer and compared with a standard FFT estimate for resolution capability. The propane transmittance spectrum was estimated by use of the FFT with a 2 to the 18th data sample interferogram, giving a maximum unapodized resolution of 0.06/cm. This estimate was then interpolated by zero filling an additional 2 to the 18th points, and the final resolution was taken to be 0.06/cm. Comparison of the maximum entropy method (MEM) estimate with the FFT was made over a 45/cm region of the spectrum for several increasing record lengths of interferogram data beginning at 2 to the 10th. It is found that over this region the MEM estimate with 2 to the 16th data samples is in close agreement with the FFT estimate using 2 to the 18th samples.

Bonavito, N. L.; Stewart, K. P.; Hurley, E. J.; Yeh, K. C.; Inguva, R.

1990-01-01

242

Retrospective Cohort Study of Bronchial Doses and Radiation-Induced Atelectasis After Stereotactic Body Radiation Therapy of Lung Tumors Located Close to the Bronchial Tree  

SciTech Connect

Purpose: To evaluate the dose–response relationship between radiation-induced atelectasis after stereotactic body radiation therapy (SBRT) and bronchial dose. Methods and Materials: Seventy-four patients treated with SBRT for tumors close to main, lobar, or segmental bronchi were selected. The association between incidence of atelectasis and bronchial dose parameters (maximum point-dose and minimum dose to the high-dose bronchial volume [ranging from 0.1 cm{sup 3} up to 2.0 cm{sup 3}]) was statistically evaluated with survival analysis models. Results: Prescribed doses varied between 4 and 20 Gy per fraction in 2-5 fractions. Eighteen patients (24.3%) developed atelectasis considered to be radiation-induced. Statistical analysis showed a significant correlation between the incidence of radiation-induced atelectasis and minimum dose to the high-dose bronchial volumes, of which 0.1 cm{sup 3} (D{sub 0.1cm3}) was used for further analysis. The median value of D{sub 0.1cm3} (?/? = 3 Gy) was EQD{sub 2,LQ} = 147 Gy{sub 3} (range, 20-293 Gy{sub 3}). For patients who developed atelectasis the median value was EQD{sub 2,LQ} = 210 Gy{sub 3}, and for patients who did not develop atelectasis, EQD{sub 2,LQ} = 105 Gy{sub 3}. Median time from treatment to development of atelectasis was 8.0 months (range, 1.1-30.1 months). Conclusion: In this retrospective study a significant dose–response relationship between the incidence of atelectasis and the dose to the high-dose volume of the bronchi is shown.

Karlsson, Kristin, E-mail: kristin.karlsson@karolinska.se [Department of Medical Physics, Karolinska University Hospital, Stockholm (Sweden); Department of Oncology-Pathology, Karolinska Institute, Stockholm (Sweden); Nyman, Jan [Department of Oncology, Sahlgrenska University Hospital, Gothenburg (Sweden); Baumann, Pia; Wersäll, Peter [Department of Oncology, Radiumhemmet, Karolinska University Hospital, Stockholm (Sweden); Department of Oncology-Pathology, Karolinska Institute, Stockholm (Sweden); Drugge, Ninni [Department of Radiation Physics, Sahlgrenska University Hospital, Gothenburg (Sweden); Gagliardi, Giovanna [Department of Medical Physics, Karolinska University Hospital, Stockholm (Sweden); Department of Oncology-Pathology, Karolinska Institute, Stockholm (Sweden); Johansson, Karl-Axel [Department of Radiation Physics, Sahlgrenska University Hospital, Gothenburg (Sweden); Persson, Jan-Olov [Statistical Research Group, Mathematical Statistics, Stockholm University, Stockholm (Sweden); Rutkowska, Eva [Physics Department, Clatterbridge Cancer Centre, Wirral (United Kingdom); Tullgren, Owe [Department of Oncology, Radiumhemmet, Karolinska University Hospital, Stockholm (Sweden); Department of Oncology-Pathology, Karolinska Institute, Stockholm (Sweden); Lax, Ingmar [Department of Medical Physics, Karolinska University Hospital, Stockholm (Sweden); Department of Oncology-Pathology, Karolinska Institute, Stockholm (Sweden)

2013-11-01

243

Maximum entropy method for reconstruction of the CMB images  

E-print Network

We propose a new approach for the accurate reconstruction of cosmic microwave background distributions from observations containing in addition to the primary fluctuations the radiation from unresolved extragalactic point sources and pixel noise. The approach uses some effective realizations of the well-known maximum entropy method and principally takes into account {\\it a priori} information about finiteness and spherical symmetry of the power spectrum of the CMB satisfying the Gaussian statistics.

A. T. Bajkova

2002-05-08

244

A mathematical approach to optimal selection of dose values in the additive dose method of ERP dosimetry  

SciTech Connect

Additive dose methods commonly used in electron paramagnetic resonance (EPR) dosimetry are time consuming and labor intensive. We have developed a mathematical approach for determining optimal spacing of applied doses and the number of spectra which should be taken at each dose level. Expected uncertainitites in the data points are assumed to be normally distributed with a fixed standard deviation and linearity of dose response is also assumed. The optimum spacing and number of points necessary for the minimal error can be estimated, as can the likely error in the resulting estimate. When low doses are being estimated for tooth enamel samples the optimal spacing is shown to be a concentration of points near the zero dose value with fewer spectra taken at a single high dose value within the range of known linearity. Optimization of the analytical process results in increased accuracy and sample throughput.

Hayes, R.B.; Haskell, E.H.; Kenner, G.H. [Utah Univ., Salt Lake City, UT (United States)

1996-01-01

245

Treatment Planning Methods in High Dose Rate Interstitial Brachytherapy of Carcinoma Cervix: A Dosimetric and Radiobiological Analysis  

PubMed Central

Treatment planning is a trial and error process that determines optimal dwell times, dose distribution, and loading pattern for high dose rate brachytherapy. Planning systems offer a number of dose calculation methods to either normalize or optimize the radiation dose. Each method has its own characteristics for achieving therapeutic dose to mitigate cancer growth without harming contiguous normal tissues. Our aim is to propose the best suited method for planning interstitial brachytherapy. 40 cervical cancer patients were randomly selected and 5 planning methods were iterated. Graphical optimization was compared with implant geometry and dose point normalization/optimization techniques using dosimetrical and radiobiological plan quality indices retrospectively. Mean tumor control probability was similar in all the methods with no statistical significance. Mean normal tissue complication probability for bladder and rectum is 0.3252 and 0.3126 (P = 0.0001), respectively, in graphical optimized plans compared to other methods. There was no significant correlation found between Conformity Index and tumor control probability when the plans were ranked according to Pearson product moment method (r = ?0.120). Graphical optimization can result in maximum sparing of normal tissues. PMID:24587919

Anbumani, Surega; Anchineyan, Pichandi; Narayanasamy, ArunaiNambiraj; Palled, Siddanna R.; Sathisan, Sajitha; Jayaraman, Punitha; Selvi, Muthu; Bilimagga, Ramesh S.

2014-01-01

246

Maximum Power Transfer Tracking in a Solar USB Charger for Smartphones  

E-print Network

Maximum Power Transfer Tracking in a Solar USB Charger for Smartphones Abstract--Battery life of commercial chargers using solar power have been developed. They focus on correct functionality, but system chargers do not perform the maximum power point tracking [2], [3] of the solar panel. We exclude

Pedram, Massoud

247

A novel method to estimate the maximum power for a photovoltaic inverter system  

Microsoft Academic Search

This paper describes a novel method to approximate the maximum power for a photovoltaic inverter system for solar distributed generation. It is designed for power systems applications and utilities. The proposed method takes in consideration the interaction between solar panels, photovoltaic inverter, maximum power point tracking (MPPT) control, solar panel DC side dynamic model and the effective intensity of light

E. I. rtiz-Rivera; Fang Peng

2004-01-01

248

Research and development of maximum power transfer tracking system for solar cell unit by matching impedance  

Microsoft Academic Search

Employing the theorem that matching impedance produces maximum power transfer, the current study develops a low-cost and highly efficient “maximum power point tracker for a solar cell unit,” for the purpose of allowing a solar cell to achieve optimal power transfer under different solar intensities and temperatures. Circuit control takes a single-chip microprocessor as the core and the booster circuit

Tun-Ping Teng; Hwa-Ming Nieh; Jiann-Jyh Chen; Yu-Cheng Lu

2010-01-01

249

Three-dimensional dose verification of the clinical application of gamma knife stereotactic radiosurgery using polymer gel and MRI  

NASA Astrophysics Data System (ADS)

This work seeks to verify multi-shot clinical applications of stereotactic radiosurgery with a Leksell Gamma Knife model C unit employing a polymer gel-MRI based experimental procedure, which has already been shown to be capable of verifying the precision and accuracy of dose delivery in single-shot gamma knife applications. The treatment plan studied in the present work resembles a clinical treatment case of pituitary adenoma using four 8 mm and one 14 mm collimator helmet shots to deliver a prescription dose of 15 Gy to the 50% isodose line (30 Gy maximum dose). For the experimental dose verification of the treatment plan, the same criteria as those used in the clinical treatment planning evaluation were employed. These included comparison of measured and GammaPlan calculated data, in terms of percentage isodose contours on axial, coronal and sagittal planes, as well as 3D plan evaluation criteria such as dose-volume histograms for the target volume, target coverage and conformity indices. Measured percentage isodose contours compared favourably with calculated ones despite individual point fluctuations at low dose contours (e.g., 20%) mainly due to the effect of T2 measurement uncertainty on dose resolution. Dose-volume histogram data were also found in a good agreement while the experimental results for the percentage target coverage and conformity index were 94% and 1.17 relative to corresponding GammaPlan calculations of 96% and 1.12, respectively. Overall, polymer gel results verified the planned dose distribution within experimental uncertainties and uncertainty related to the digitization process of selected GammaPlan output data.

Papagiannis, P.; Karaiskos, P.; Kozicki, M.; Rosiak, J. M.; Sakelliou, L.; Sandilos, P.; Seimenis, I.; Torrens, M.

2005-05-01

250

Three-dimensional dose verification of the clinical application of gamma knife stereotactic radiosurgery using polymer gel and MRI.  

PubMed

This work seeks to verify multi-shot clinical applications of stereotactic radiosurgery with a Leksell Gamma Knife model C unit employing a polymer gel-MRI based experimental procedure, which has already been shown to be capable of verifying the precision and accuracy of dose delivery in single-shot gamma knife applications. The treatment plan studied in the present work resembles a clinical treatment case of pituitary adenoma using four 8 mm and one 14 mm collimator helmet shots to deliver a prescription dose of 15 Gy to the 50% isodose line (30 Gy maximum dose). For the experimental dose verification of the treatment plan, the same criteria as those used in the clinical treatment planning evaluation were employed. These included comparison of measured and GammaPlan calculated data, in terms of percentage isodose contours on axial, coronal and sagittal planes, as well as 3D plan evaluation criteria such as dose-volume histograms for the target volume, target coverage and conformity indices. Measured percentage isodose contours compared favourably with calculated ones despite individual point fluctuations at low dose contours (e.g., 20%) mainly due to the effect of T2 measurement uncertainty on dose resolution. Dose-volume histogram data were also found in a good agreement while the experimental results for the percentage target coverage and conformity index were 94% and 1.17 relative to corresponding GammaPlan calculations of 96% and 1.12, respectively. Overall, polymer gel results verified the planned dose distribution within experimental uncertainties and uncertainty related to the digitization process of selected GammaPlan output data. PMID:15843731

Papagiannis, P; Karaiskos, P; Kozicki, M; Rosiak, J M; Sakelliou, L; Sandilos, P; Seimenis, I; Torrens, M

2005-05-01

251

Oral anticancer drugs: how limited dosing options and dose reductions may affect outcomes in comparative trials and efficacy in patients.  

PubMed

Historically, cancer medicine has avoided the problem of unequal dosing by comparing maximum-tolerated doses of intravenous regimens with proportionate dose reductions for toxicity. However, in recent years, with the development of numerous oral anticancer agents, dosing options are arbitrarily and increasingly limited by the size of pills. We contend that an underappreciated consequence of pill size is unequal dosing in comparative clinical trials and that this can have an impact on outcomes. We discuss how comparative effectiveness trials can be unbalanced and how the use of doses that are not sustainable might affect outcomes, especially marginal ones. We further argue that because of their poor tolerability and their limited dosing options, which often result in large dose adjustments in response to toxicity, the real-world clinical effectiveness of oral anticancer agents may be diminished and may not emulate results achieved in registration trials. PMID:24711558

Prasad, Vinay; Massey, Paul R; Fojo, Tito

2014-05-20

252

Uncertainties on lung doses from inhaled plutonium.  

PubMed

In a recent epidemiological study, Bayesian uncertainties on lung doses have been calculated to determine lung cancer risk from occupational exposures to plutonium. These calculations used a revised version of the Human Respiratory Tract Model (HRTM) published by the ICRP. In addition to the Bayesian analyses, which give probability distributions of doses, point estimates of doses (single estimates without uncertainty) were also provided for that study using the existing HRTM as it is described in ICRP Publication 66; these are to be used in a preliminary analysis of risk. To infer the differences between the point estimates and Bayesian uncertainty analyses, this paper applies the methodology to former workers of the United Kingdom Atomic Energy Authority (UKAEA), who constituted a subset of the study cohort. The resulting probability distributions of lung doses are compared with the point estimates obtained for each worker. It is shown that mean posterior lung doses are around two- to fourfold higher than point estimates and that uncertainties on doses vary over a wide range, greater than two orders of magnitude for some lung tissues. In addition, we demonstrate that uncertainties on the parameter values, rather than the model structure, are largely responsible for these effects. Of these it appears to be the parameters describing absorption from the lungs to blood that have the greatest impact on estimates of lung doses from urine bioassay. Therefore, accurate determination of the chemical form of inhaled plutonium and the absorption parameter values for these materials is important for obtaining reliable estimates of lung doses and hence risk from occupational exposures to plutonium. PMID:21692652

Puncher, Matthew; Birchall, Alan; Bull, Richard K

2011-10-01

253

Determining the effects of microsphere and surrounding material composition on {sup 90}Y dose kernels using egsnrc and mcnp5  

SciTech Connect

Purpose: Recent advances in the imaging of {sup 90}Y using positron emission tomography (PET) and improved uncertainty in the branching ratio for the internal pair production component of {sup 90}Y decay allow for a more accurate determination of the activity distribution of {sup 90}Y microspheres within a patient. This improved activity distribution can be convolved with the dose kernel of {sup 90}Y to calculate the dose distribution within a patient. This work investigates the effects of microsphere and surrounding material composition on {sup 90}Y dose kernels using egsnrc and mcnp5 and compares the results of these two transport codes. Methods: Monte Carlo simulations were performed with egsnrc and mcnp5 to calculate the dose rate at multiple radial distances around various {sup 90}Y sources. Point source simulations were completed with mcnp5 to determine the optimal electron transport settings for this work. After determining the optimal settings, point source simulations were completed using egsnrc (user code edknrc) and mcnp5 in water and liver [as defined by the International Commission on Radiation Units and Measurements (ICRU) Report 44]. The results were compared to ICRU Report 72 reference data. Point source simulations were also completed in water with a density of 1.06 g{center_dot}cm{sup -3} to evaluate the effect of the density of the surrounding material. Glass and resin microsphere simulations were performed with average and maximum diameter and density values (based on values given in the literature) in water and in liver. The results were compared to point source simulation results using the same transport code and in the same surrounding material. All simulations had statistical uncertainties less than 1%. Results: The optimal transport settings in mcnp5 for this work included using the energy-and step-specific algorithm (DBCN 17J 2) and ESTEP set to 10. These settings were used for all subsequent simulations with mcnp5. The point source simulations in water for both egsnrc and mcnp5 were found to agree within 2% of the ICRU 72 reference data over the investigated range. Point source simulations in liver had large differences relative to ICRU 72, approaching -60% near the maximum range of {sup 90}Y. These differences are mostly attributed to the difference in density between water (1.0 g{center_dot}cm{sup -3}) and liver (1.06 g{center_dot}cm{sup -3}). Glass and resin microsphere simulations showed a slight decrease in the dose rate near the maximum range of {sup 90}Y relative to the point source simulations. The largest relative differences were approximately -4.2% and -2.8% for the glass and resin microspheres, respectively. Agreement between the egsnrc and mcnp5 simulations results was generally good. Conclusions: The presence of the microsphere material causes slight differences in the {sup 90}Y dose kernel compared to those calculated with point sources. Large differences were seen between simulations in water and those in liver. For the most accurate calculation of the dose distribution, the density of the patient's liver should be accounted for in the calculation of the dose kernel. Lastly, due to the need to determine the optimal transport settings with mcnp5, electron transport with this code should be used with caution.

Paxton, Adam B.; Davis, Stephen D.; DeWerd, Larry A. [Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705 (United States); Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705 and McGill University Health Centre, Department of Medical Physics, Montreal, Quebec H3G 1A4 (Canada); Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705 (United States)

2012-03-15

254

Calculate Your Radiation Dose  

MedlinePLUS

... Do you live within 50 miles of a nuclear power plant? Do you live within 50 miles of a coal fired power plant? TOTAL YEARLY DOSE (in mrem) ... the American Nuclear Society's brochure, "Personal Radiation Dose Chart". The primary ...

255

Maximum likelihood training of probabilistic neural networks  

Microsoft Academic Search

A maximum likelihood method is presented for training probabilistic neural networks (PNN's) using a Gaussian kernel, or Parzen window. The proposed training algorithm enables general nonlinear discrimination and is a generalization of Fisher's method for linear discrimination. Important features of maximum likelihood training for PNN's are: 1) it economizes the well known Parzen window estimator while preserving feedforward NN architecture,

Roy L. Streit; Tod E. Luginbuhl

1994-01-01

256

Learning Markov Structure by Maximum Entropy Relaxation  

E-print Network

the maximum entropy re- laxation (MER) within an exponential fam- ily, which maximizes entropy subject to con on a set of statis- tics, the entropy-maximizing distribution among all distributions liesLearning Markov Structure by Maximum Entropy Relaxation Jason K. Johnson, Venkat Chandrasekaran

Willsky, Alan S.

257

Inverse maximum flow and minimum cut problems  

Microsoft Academic Search

In this paper we consider two inverse problems in combinatorial optimization: inverse maximum flow (IMF) problem and inverse minimum cut (IMC) problem. IMF (or IMC) problem can be described as: how to change the capacity vector C of a network as little as possible so that a given flow (or cut) becomes a maximum flow (or minimum cut) in the

C. Yang; J. Zhang; Z. Ma

1997-01-01

258

Maximum Allowable Load of Two Cooperative Manipulators  

Microsoft Academic Search

In this paper a computational technique for determining the maximum allowable load of two cooperative manipulators for a desired trajectory of the load is presented. There are number of factors that limit the maximum allowable load of two cooperative robotic arms. With attention to configuration of cooperative manipulators with redundant actuation as a closed form chain, the most important limitation

H. Ghariblu; A. Javanmard

2010-01-01

259

Estimating landscape carrying capacity through maximum clique analysis.  

PubMed

Habitat suitability (HS) maps are widely used tools in wildlife science and establish a link between wildlife populations and landscape pattern. Although HS maps spatially depict the distribution of optimal resources for a species, they do not reveal the population size a landscape is capable of supporting--information that is often crucial for decision makers and managers. We used a new approach, "maximum clique analysis," to demonstrate how HS maps for territorial species can be used to estimate the carrying capacity, N(k), of a given landscape. We estimated the N(k) of Ovenbirds (Seiurus aurocapillus) and bobcats (Lynx rufus) in an 1153-km2 study area in Vermont, USA. These two species were selected to highlight different approaches in building an HS map as well as computational challenges that can arise in a maximum clique analysis. We derived 30-m2 HS maps for each species via occupancy modeling (Ovenbird) and by resource utilization modeling (bobcats). For each species, we then identified all pixel locations on the map (points) that had sufficient resources in the surrounding area to maintain a home range (termed a "pseudo-home range"). These locations were converted to a mathematical graph, where any two points were linked if two pseudo-home ranges could exist on the landscape without violating territory boundaries. We used the program Cliquer to find the maximum clique of each graph. The resulting estimates of N(k) = 236 Ovenbirds and N(k) = 42 female bobcats were sensitive to different assumptions and model inputs. Estimates of N(k) via alternative, ad hoc methods were 1.4 to > 30 times greater than the maximum clique estimate, suggesting that the alternative results may be upwardly biased. The maximum clique analysis was computationally intensive but could handle problems with < 1500 total pseudo-home ranges (points). Given present computational constraints, it is best suited for species that occur in clustered distributions (where the problem can be broken into several, smaller problems), or for species with large home ranges relative to grid scale where resampling the points to a coarser resolution can reduce the problem to manageable proportions. PMID:23387124

Donovan, Therese M; Warrington, Gregory S; Schwenk, W Scott; Dinitz, Jeffrey H

2012-12-01

260

A simple method of independent treatment time verification in gamma knife radiosurgery using integral dose.  

PubMed

The purpose of this study is to develop a simple independent dose calculation method to verify treatment plans for Leksell Gamma Knife radiosurgery. Our approach uses the total integral dose within the skull as an end point for comparison. The total integral dose is computed using a spreadsheet and is compared to that obtained from Leksell GammaPlan. It is calculated as the sum of the integral doses of 201 beams, each passing through a cylindrical volume. The average length of the cylinders is estimated from the Skull-Scaler measurement data taken before treatment. Correction factors are applied to the length of the cylinder depending on the location of a shot in the skull. The radius of the cylinder corresponds to the collimator aperture of the helmet, with a correction factor for the beam penumbra and scattering. We have tested our simple spreadsheet program using treatment plans of 40 patients treated with Gamma Knife in our center. These patients differ in geometry, size, lesion locations, collimator helmet, and treatment complexities. Results show that differences between our calculations and treatment planning results are typically within +/-3%, with a maximum difference of +/-3.8%. We demonstrate that our spreadsheet program is a convenient and effective independent method to verify treatment planning irradiation times prior to implementation of Gamma Knife radiosurgery. PMID:15651617

Jin, Jian-Yue; Drzymala, Robert; Li, Zuofeng

2004-12-01

261

A simple method of independent treatment time verification in gamma knife radiosurgery using integral dose  

SciTech Connect

The purpose of this study is to develop a simple independent dose calculation method to verify treatment plans for Leksell Gamma Knife radiosurgery. Our approach uses the total integral dose within the skull as an end point for comparison. The total integral dose is computed using a spreadsheet and is compared to that obtained from Leksell GammaPlan registered . It is calculated as the sum of the integral doses of 201 beams, each passing through a cylindrical volume. The average length of the cylinders is estimated from the Skull-Scaler measurement data taken before treatment. Correction factors are applied to the length of the cylinder depending on the location of a shot in the skull. The radius of the cylinder corresponds to the collimator aperture of the helmet, with a correction factor for the beam penumbra and scattering. We have tested our simple spreadsheet program using treatment plans of 40 patients treated with Gamma Knife registered in our center. These patients differ in geometry, size, lesion locations, collimator helmet, and treatment complexities. Results show that differences between our calculations and treatment planning results are typically within {+-}3%, with a maximum difference of {+-}3.8%. We demonstrate that our spreadsheet program is a convenient and effective independent method to verify treatment planning irradiation times prior to implementation of Gamma Knife radiosurgery.

Jin Jianyue; Drzymala, Robert; Li Zuofeng [Department of Radiation Oncology, Siteman Cancer Center, Washington University Medical Center, St. Louis, Missouri 63110 (United States)

2004-12-01

262

Fitting Emax models to clinical trial dose-response data when the high dose asymptote is ill defined.  

PubMed

We consider fitting the so-called Emax model to continuous response data from clinical trials designed to investigate the dose-response relationship for an experimental compound. When there is insufficient information in the data to estimate all of the parameters because of the high dose asymptote being ill defined, maximum likelihood estimation fails to converge. We explore the use of either bootstrap resampling or the profile likelihood to make inferences about effects and doses required to give a particular effect, using limits on the parameter values to obtain the value of the maximum likelihood when the high dose asymptote is ill defined. The results obtained show these approaches to be comparable with or better than some others that have been used when maximum likelihood estimation fails to converge and that the profile likelihood method outperforms the method of bootstrap resampling used. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25228394

Brain, P; Kirby, S; Larionov, R

2014-11-01

263

Maximum stellar mass versus cluster membership number revisited  

E-print Network

We have made a new compilation of observations of maximum stellar mass versus cluster membership number from the literature, which we analyse for consistency with the predictions of a simple random drawing hypothesis for stellar mass selection in clusters. Previously, Weidner and Kroupa have suggested that the maximum stellar mass is lower, in low mass clusters, than would be expected on the basis of random drawing, and have pointed out that this could have important implications for steepening the integrated initial mass function of the Galaxy (the IGIMF) at high masses. Our compilation demonstrates how the observed distribution in the plane of maximum stellar mass versus membership number is affected by the method of target selection; in particular, rather low n clusters with large maximum stellar masses are abundant in observational datasets that specifically seek clusters in the environs of high mass stars. Although we do not consider our compilation to be either complete or unbiased, we discuss the method by which such data should be statistically analysed. Our very provisional conclusion is that the data is not indicating any striking deviation from the expectations of random drawing.

Th. Maschberger; C. J. Clarke

2008-08-29

264

Triadic conceptual structure of the maximum entropy approach to evolution.  

PubMed

Many problems in evolutionary theory are cast in dyadic terms, such as the polar oppositions of organism and environment. We argue that a triadic conceptual structure offers an alternative perspective under which the information generating role of evolution as a physical process can be analyzed, and propose a new diagrammatic approach. Peirce's natural philosophy was deeply influenced by his reception of both Darwin's theory and thermodynamics. Thus, we elaborate on a new synthesis which puts together his theory of signs and modern Maximum Entropy approaches to evolution in a process discourse. Following recent contributions to the naturalization of Peircean semiosis, pointing towards 'physiosemiosis' or 'pansemiosis', we show that triadic structures involve the conjunction of three different kinds of causality, efficient, formal and final. In this, we accommodate the state-centered thermodynamic framework to a process approach. We apply this on Ulanowicz's analysis of autocatalytic cycles as primordial patterns of life. This paves the way for a semiotic view of thermodynamics which is built on the idea that Peircean interpretants are systems of physical inference devices evolving under natural selection. In this view, the principles of Maximum Entropy, Maximum Power, and Maximum Entropy Production work together to drive the emergence of information carrying structures, which at the same time maximize information capacity as well as the gradients of energy flows, such that ultimately, contrary to Schrödinger's seminal contribution, the evolutionary process is seen to be a physical expression of the Second Law. PMID:21055440

Herrmann-Pillath, Carsten; Salthe, Stanley N

2011-03-01

265

MPI Point-to-Point Communication  

NSDL National Science Digital Library

This module details and differentiates the various types of point-to-point communication available in MPI. Point-to-point communication involves transmission of a message between a pair of processes, as opposed to collective communication, which involves a group of processes.

266

Design of a prospective, dose-escalation study evaluating the Safety of Pioglitazone for Hematoma Resolution in Intracerebral Hemorrhage (SHRINC).  

PubMed

RATIONALE?: Preclinical work demonstrates that the transcription factor peroxisome proliferator-activated receptor gamma plays an important role in augmenting phagocytosis while modulating oxidative stress and inflammation. We propose that targeted stimulation of phagocytosis to promote efficient removal of the hematoma without harming surrounding brain cells may be a therapeutic option for intracerebral hemorrhage. AIMS?: The primary objective is to assess the safety of the peroxisome proliferator-activated receptor gamma agonist, pioglitazone, in increasing doses for three-days followed by a maintenance dose, when administered to patients with spontaneous intracerebral hemorrhage within 24?h of symptom onset compared with standard care. We will determine the maximum tolerated dose of pioglitazone. STUDY DESIGN?: This is a prospective, randomized, blinded, placebo-controlled, dose-escalation safety trial in which patients with spontaneous intracerebral hemorrhage are randomly allocated to placebo or treatment. The Continual Reassessment Method for dose finding is used to determine the maximum tolerated dose of pioglitazone. Hematoma and edema resolution is evaluated with serial magnetic resonance imaging (MRI) at specified time points. Functional outcome will be evaluated at three- and six-months. OUTCOMES?: The primary safety outcome is mortality at discharge. Secondary safety outcomes include mortality at three-months and six-months, symptomatic cerebral edema, clinically significant congestive heart failure, edema, hypoglycemia, anemia, and hepatotoxicity. Radiographic outcomes will explore the time frame for resolution of 25%, 50%, and 75% of the hematoma. Clinical outcomes are measured by the National Institutes of Health Stroke Scale (NIHSS), the Barthel Index, modified Rankin Scale, Stroke Impact Scale-16, and EuroQol at three- and six-months. PMID:22340518

Gonzales, Nicole R; Shah, Jharna; Sangha, Navdeep; Sosa, Lenis; Martinez, Rebecca; Shen, Loren; Kasam, Mallikarjunarao; Morales, Miriam M; Hossain, M Monir; Barreto, Andrew D; Savitz, Sean I; Lopez, George; Misra, Vivek; Wu, Tzu-Ching; El Khoury, Ramy; Sarraj, Amrou; Sahota, Preeti; Hicks, William; Acosta, Indrani; Sline, M Rick; Rahbar, Mohammad H; Zhao, Xiurong; Aronowski, Jaroslaw; Grotta, James C

2013-07-01

267

Application of a Novel Dose-Uncertainty Model for Dose-Uncertainty Analysis in Prostate Intensity-Modulated Radiotherapy  

SciTech Connect

Purpose: To analyze dose uncertainty using a previously published dose-uncertainty model, and to assess potential dosimetric risks existing in prostate intensity-modulated radiotherapy (IMRT). Methods and Materials: The dose-uncertainty model provides a three-dimensional (3D) dose-uncertainty distribution in a given confidence level. For 8 retrospectively selected patients, dose-uncertainty maps were constructed using the dose-uncertainty model at the 95% CL. In addition to uncertainties inherent to the radiation treatment planning system, four scenarios of spatial errors were considered: machine only (S1), S1 + intrafraction, S1 + interfraction, and S1 + both intrafraction and interfraction errors. To evaluate the potential risks of the IMRT plans, three dose-uncertainty-based plan evaluation tools were introduced: confidence-weighted dose-volume histogram, confidence-weighted dose distribution, and dose-uncertainty-volume histogram. Results: Dose uncertainty caused by interfraction setup error was more significant than that of intrafraction motion error. The maximum dose uncertainty (95% confidence) of the clinical target volume (CTV) was smaller than 5% of the prescribed dose in all but two cases (13.9% and 10.2%). The dose uncertainty for 95% of the CTV volume ranged from 1.3% to 2.9% of the prescribed dose. Conclusions: The dose uncertainty in prostate IMRT could be evaluated using the dose-uncertainty model. Prostate IMRT plans satisfying the same plan objectives could generate a significantly different dose uncertainty because a complex interplay of many uncertainty sources. The uncertainty-based plan evaluation contributes to generating reliable and error-resistant treatment plans.

Jin Hosang [University of Florida Proton Therapy Institute, University of Florida, Jacksonville, FL (United States); Palta, Jatinder R. [Department of Radiation Oncology, University of Florida, Gainesville, FL (United States); Kim, You-Hyun [Department of Radiologic Science, Korea University, Seoul (Korea, Republic of); Kim, Siyong, E-mail: kim.siyong@mayo.ed [Department of Radiation Oncology, Mayo Clinic Jacksonville, Jacksonville, FL (United States)

2010-11-01

268

Occupational radiation doses to the extremities and the eyes in interventional radiology and cardiology procedures  

PubMed Central

Objectives The aim of this study was to determine occupational dose levels in interventional radiology and cardiology procedures. Methods The study covered a sample of 25 procedures and monitored occupational dose for all laboratory personnel. Each individual wore eight thermoluminescent dosemeters next to the eyes, wrists, fingers and legs during each procedure. Radiation protection shields used in each procedure were recorded. Results The highest doses per procedure were recorded for interventionists at the left wrist (average 485 ?Sv, maximum 5239 ?Sv) and left finger (average 324 ?Sv, maximum 2877 ?Sv), whereas lower doses were recorded for the legs (average 124 ?Sv, maximum 1959 ?Sv) and the eyes (average 64 ?Sv, maximum 1129 ?Sv). Doses to the assisting nurses during the intervention were considerably lower; the highest doses were recorded at the wrists (average 26 ?Sv, maximum 41 ?Sv) and legs (average 18 ?Sv, maximum 22 ?Sv), whereas doses to the eyes were minimal (average 4 ?Sv, maximum 16 ?Sv). Occupational doses normalised to kerma area product (KAP) ranged from 11.9 to 117.3 ?Sv/1000 cGy cm2 and KAP was poorly correlated to the interventionists' extremity doses. Conclusion Calculation of the dose burden for interventionists considering the actual number of procedures performed annually revealed that dose limits for the extremities and the lenses of the eyes were not exceeded. However, there are cases in which high doses have been recorded and this can lead to exceeding the dose limits when bad practices are followed and the radiation protection tools are not properly used. PMID:21172967

Efstathopoulos, E P; Pantos, I; Andreou, M; Gkatzis, A; Carinou, E; Koukorava, C; Kelekis, N L; Brountzos, E

2011-01-01

269

Dose-response stability and integrity of the dose distribution of various polymer gel dosimeters  

NASA Astrophysics Data System (ADS)

In this study the stability of different polymer gel dosimeters is investigated. Further to a previous chemical stability study on a (6%T, 50%C) PAG gel, the change in slope and intercept of the linear part of the R2-dose plot is recorded with time for different gel formulations. In addition to this R2-dose-response stability study, the dose edge of a half-blocked field was recorded with time. Three different PAG type polymer gels, a hydroxyethyl acrylate (HEA) gel and two different normoxic polymer gels were investigated. In the PAG type polymer gels, the relative concentration of gelatin and comonomers was varied in order to study the influence of the different components, that constitute the dosimeter, on the stability. It is shown that the R2-dose-response stability is largely determined by the chemical composition of the gel dosimeters. All the PAG gel dosimeters and the normoxic gel dosimeters are found to preserve the integrity of the dose distribution up to 22 days after irradiation. The half-life of the change in dose sensitivity of a MAGIC gel is found to be 18 h compared to 5.7 h for a (6%T, 50%C) PAG gel. A maximum relative decrease in dose sensitivity of 21% was noted for the MAGIC gel compared to an increase of 50% for a (6%T, 50%C) PAG gel. A loss of integrity of the dose distribution was found in the HEA gel.

DeDeene, Y.; Venning, A.; Hurley, C.; Healy, B. J.; Baldock, C.

2002-07-01

270

75 FR 43840 - Inflation Adjustment of the Ordinary Maximum and Aggravated Maximum Civil Monetary Penalties for...  

Federal Register 2010, 2011, 2012, 2013

FRA is adjusting the ordinary maximum penalty and the aggravated maximum penalty that it will apply when assessing a civil monetary penalty for a violation of the Federal hazardous material transportation laws or a regulation, special permit, or approval issued under those laws. The aggravated maximum penalty is available only for a violation that results in death, serious illness, or severe......

2010-07-27

271

Validation of the photon dose calculation model in the VARSKIN 4 skin dose computer code.  

PubMed

An updated version of the skin dose computer code VARSKIN, namely VARSKIN 4, was examined to determine the accuracy of the photon model in calculating dose rates with different combinations of source geometry and radionuclides. The reference data for this validation were obtained by means of Monte Carlo transport calculations using MCNP5. The geometries tested included the zero volume sources point and disc, as well as the volume sources sphere and cylinder. Three geometries were tested using source directly on the skin, source off the skin with an absorber material between source and skin, and source off the skin with only an air gap between source and skin. The results of these calculations showed that the non-volume sources produced dose rates that were in very good agreement with the Monte Carlo calculations, but the volume sources resulted in overestimates of the dose rates compared with the Monte Carlo results by factors that ranged up to about 2.5. The results for the air gap showed poor agreement with Monte Carlo for all source geometries, with the dose rates overestimated in all cases. The conclusion was that, for situations where the beta dose is dominant, these results are of little significance because the photon dose in such cases is generally a very small fraction of the total dose. For situations in which the photon dose is dominant, use of the point or disc geometries should be adequate in most cases except those in which the dose approaches or exceeds an applicable limit. Such situations will often require a more accurate dose assessment and may require the use of methods such as Monte Carlo transport calculations. PMID:23111523

Sherbini, Sami; Decicco, Joseph; Struckmeyer, Richard; Saba, Mohammad; Bush-Goddard, Stephanie

2012-12-01

272

Photoemission spectromicroscopy with MAXIMUM at Wisconsin  

NASA Astrophysics Data System (ADS)

We describe the development of the scanning photoemission spectromicroscope MAXIMUM at the Wisoncsin Synchrotron Radiation Center, which uses radiation from a 30-period undulator. The article includes a discussion of the first tests after the initial commissioning.

Ng, W.; Ray-Chaudhuri, A. K.; Cole, R. K.; Wallace, J.; Crossley, S.; Crossley, D.; Chen, G.; Green, M.; Guo, J.; Hansen, R. W. C.; Cerrina, F.; Margaritondo, G.; Underwood, J. H.; Korthright, J.; Perera, R. C. C.

1990-06-01

273

On the efficiency at maximum cooling power  

NASA Astrophysics Data System (ADS)

The efficiency at maximum power (EMP) of heat engines operating as generators is one corner stone of finite-time thermodynamics, the Curzon-Ahlborn efficiency \\eta_CA being considered as a universal upper bound. Yet, no valid counterpart to \\eta_CA has been derived for the efficiency at maximum cooling power (EMCP) for heat engines operating as refrigerators. In this letter we analyse the reasons of the failure to obtain such a bound and we demonstrate that, despite the introduction of several optimisation criteria, the maximum cooling power condition should be considered as the genuine equivalent of maximum power condition in the finite-time thermodynamics frame. We then propose and discuss an analytic expression for the EMCP in the specific case of exoreversible refrigerators.

Apertet, Y.; Ouerdane, H.; Michot, A.; Goupil, C.; Lecoeur, Ph.

2013-08-01

274

A dual method for maximum entropy restoration  

NASA Technical Reports Server (NTRS)

A simple iterative dual algorithm for maximum entropy image restoration is presented. The dual algorithm involves fewer parameters than conventional minimization in the image space. Minicomputer test results for Fourier synthesis with inadequate phantom data are given.

Smith, C. B.

1979-01-01

275

The Minimum Cannot Become the Maximum.  

ERIC Educational Resources Information Center

In this paper the author shares his concerns about minimal competency testing, fearing that the minimum may become the maximum. He discusses this fear based on examples from the English curriculum--Language, Writing, and Literature. (KC)

Bushman, John H.

1980-01-01

276

Incremental Network Design with Maximum Flows  

E-print Network

Dec 21, 2013 ... We study an incremental network design problem, where in each time period of ... In a series of computational experiments, we compare ...... maximum flow (F - f), the number of instances not solved to optimality within the time.

2013-12-21

277

5 CFR 534.203 - Maximum stipends.  

Code of Federal Regulations, 2011 CFR

...Maximum stipends for positions in the Public Health Service in which duty requires intimate contact with persons afflicted with leprosy are increased above the rates prescribed in paragraph (a) of this section to the same extent that additional pay is...

2011-01-01

278

5 CFR 534.203 - Maximum stipends.  

Code of Federal Regulations, 2013 CFR

...Maximum stipends for positions in the Public Health Service in which duty requires intimate contact with persons afflicted with leprosy are increased above the rates prescribed in paragraph (a) of this section to the same extent that additional pay is...

2013-01-01

279

5 CFR 534.203 - Maximum stipends.  

Code of Federal Regulations, 2012 CFR

...Maximum stipends for positions in the Public Health Service in which duty requires intimate contact with persons afflicted with leprosy are increased above the rates prescribed in paragraph (a) of this section to the same extent that additional pay is...

2012-01-01

280

14 CFR 65.47 - Maximum hours.  

...CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators § 65.47 Maximum hours. Except in an emergency, a certificated air traffic control tower operator must be relieved of all duties...

2014-01-01

281

14 CFR 65.47 - Maximum hours.  

Code of Federal Regulations, 2013 CFR

...CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators § 65.47 Maximum hours. Except in an emergency, a certificated air traffic control tower operator must be relieved of all duties...

2013-01-01

282

14 CFR 65.47 - Maximum hours.  

Code of Federal Regulations, 2011 CFR

...CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators § 65.47 Maximum hours. Except in an emergency, a certificated air traffic control tower operator must be relieved of all duties...

2011-01-01

283

14 CFR 65.47 - Maximum hours.  

Code of Federal Regulations, 2012 CFR

...CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators § 65.47 Maximum hours. Except in an emergency, a certificated air traffic control tower operator must be relieved of all duties...

2012-01-01

284

14 CFR 65.47 - Maximum hours.  

Code of Federal Regulations, 2010 CFR

...CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators § 65.47 Maximum hours. Except in an emergency, a certificated air traffic control tower operator must be relieved of all duties...

2010-01-01

285

Maximum-Likelihood Detection Of Noncoherent CPM  

NASA Technical Reports Server (NTRS)

Simplified detectors proposed for use in maximum-likelihood-sequence detection of symbols in alphabet of size M transmitted by uncoded, full-response continuous phase modulation over radio channel with additive white Gaussian noise. Structures of receivers derived from particular interpretation of maximum-likelihood metrics. Receivers include front ends, structures of which depends only on M, analogous to those in receivers of coherent CPM. Parts of receivers following front ends have structures, complexity of which would depend on N.

Divsalar, Dariush; Simon, Marvin K.

1993-01-01

286

Maximum-Likelihood Parameter-Estimation Algorithm  

NASA Technical Reports Server (NTRS)

Efficient version of maximum-likelihood algorithm devised for calculating normal-mode frequencies and damping parameters of vibrating system from experimental data where both process noise and measurement noise present. Method applicable in vibration analysis of such complicated structures as vehicles, aircraft, and spacecraft. New algorithm simplification of existing maximum-likelihood formulation using Kalman filter that allows for both process and measurement noise.

Eldred, D. B.; Hamidi, M.; Rodriguez, G.

1986-01-01

287

Shape-enhanced maximum intensity projection  

Microsoft Academic Search

Maximum intensity projection (MIP) displays the voxel with the maximum intensity along the viewing ray, and this offers simplicity\\u000a in usage, as it does not require a complex transfer function, the specification of which is a highly challenging and time-consuming\\u000a process in direct volume rendering (DVR). However, MIP also has its inherent limitation, the loss of spatial context and shape

Zhiguang Zhou; Yubo Tao; Hai Lin; Feng Dong; Gordon Clapworthy

2011-01-01

288

Theoretical maximum concentration factors for solar concentrators  

SciTech Connect

The theoretical maximum concentration factors are determined for different definitions of the factor for two-dimensional and three-dimensional solar concentrators that are valid for any source with nonuniform intensity distribution. Results are obtained starting from those derived by Winston (1970) for Lambertian sources. In particular, maximum concentration factors for three models of the solar-disk intensity distribution are calculated. 12 references.

Nicolas, R.O.; Duran, J.C.

1984-11-01

289

The measurement of maximum cylinder pressures  

NASA Technical Reports Server (NTRS)

The work presented in this report was undertaken at the Langley Memorial Aeronautical Laboratory of the National Advisory Committee for Aeronautics to determine a suitable method for measuring the maximum pressures occurring in aircraft engine cylinders. The study and development of instruments for the measurement of maximum cylinder pressures has been conducted in connection with carburetor and oil engine investigations on a single cylinder aircraft-type engine. Five maximum cylinder-pressure devices have been designed, and tested, in addition to the testing of three commercial indicators. Values of maximum cylinder pressures are given as obtained with various indicators for the same pressures and for various kinds and values of maximum cylinder pressures, produced chiefly by variation of the injection advance angle in high-speed oil engine. The investigations indicate that the greatest accuracy in determining maximum cylinder pressures can be obtained with an electric, balanced-pressure, diaphragm or disk-type indicator so constructed as to have a diaphragm or disk of relatively large area and minimum seat width and mass.

Hicks, Chester W

1929-01-01

290

Point set registration: coherent point drift.  

PubMed

Point set registration is a key component in many computer vision tasks. The goal of point set registration is to assign correspondences between two sets of points and to recover the transformation that maps one point set to the other. Multiple factors, including an unknown nonrigid spatial transformation, large dimensionality of point set, noise, and outliers, make the point set registration a challenging problem. We introduce a probabilistic method, called the Coherent Point Drift (CPD) algorithm, for both rigid and nonrigid point set registration. We consider the alignment of two point sets as a probability density estimation problem. We fit the Gaussian mixture model (GMM) centroids (representing the first point set) to the data (the second point set) by maximizing the likelihood. We force the GMM centroids to move coherently as a group to preserve the topological structure of the point sets. In the rigid case, we impose the coherence constraint by reparameterization of GMM centroid locations with rigid parameters and derive a closed form solution of the maximization step of the EM algorithm in arbitrary dimensions. In the nonrigid case, we impose the coherence constraint by regularizing the displacement field and using the variational calculus to derive the optimal transformation. We also introduce a fast algorithm that reduces the method computation complexity to linear. We test the CPD algorithm for both rigid and nonrigid transformations in the presence of noise, outliers, and missing points, where CPD shows accurate results and outperforms current state-of-the-art methods. PMID:20975122

Myronenko, Andriy; Song, Xubo

2010-12-01

291

Effect of Breathing Motion on Radiotherapy Dose Accumulation in the Abdomen Using Deformable Registration  

SciTech Connect

Purpose: To investigate the effect of breathing motion and dose accumulation on the planned radiotherapy dose to liver tumors and normal tissues using deformable image registration. Methods and Materials: Twenty-one free-breathing stereotactic liver cancer radiotherapy patients, planned on static exhale computed tomography (CT) for 27-60 Gy in six fractions, were included. A biomechanical model-based deformable image registration algorithm retrospectively deformed each exhale CT to inhale CT. This deformation map was combined with exhale and inhale dose grids from the treatment planning system to accumulate dose over the breathing cycle. Accumulation was also investigated using a simple rigid liver-to-liver registration. Changes to tumor and normal tissue dose were quantified. Results: Relative to static plans, mean dose change (range) after deformable dose accumulation (as % of prescription dose) was -1 (-14 to 8) to minimum tumor, -4 (-15 to 0) to maximum bowel, -4 (-25 to 1) to maximum duodenum, 2 (-1 to 9) to maximum esophagus, -2 (-13 to 4) to maximum stomach, 0 (-3 to 4) to mean liver, and -1 (-5 to 1) and -2 (-7 to 1) to mean left and right kidneys. Compared to deformable registration, rigid modeling had changes up to 8% to minimum tumor and 7% to maximum normal tissues. Conclusion: Deformable registration and dose accumulation revealed potentially significant dose changes to either a tumor or normal tissue in the majority of cases as a result of breathing motion. These changes may not be accurately accounted for with rigid motion.

Velec, Michael, E-mail: michael.velec@rmp.uhn.on.c [Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto (Canada); Moseley, Joanne L. [Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto (Canada); Eccles, Cynthia L.; Craig, Tim; Sharpe, Michael B.; Dawson, Laura A. [Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto (Canada); Department of Radiation Oncology, University of Toronto, Toronto (Canada); Brock, Kristy K. [Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto (Canada); Department of Radiation Oncology, University of Toronto, Toronto (Canada); Department of Medical Biophysics, University of Toronto, Toronto (Canada)

2011-05-01

292

Liposomal Bupivacaine as a Single-Injection Peripheral Nerve Block: A Dose-Response Study  

PubMed Central

Background Currently available local anesthetics approved for single-injection peripheral nerve blocks have a maximum duration less than 24 hours. A liposomal bupivacaine formulation (EXPAREL®, Pacira Pharmaceuticals, Inc., San Diego, California), releasing bupivacaine over 96 hours, recently gained Food and Drug Administration approval exclusively for wound infiltration, but not peripheral nerve blocks. Methods Bilateral single-injection femoral nerve blocks were administered in healthy volunteers (n=14). For each block, liposomal bupivacaine (0–80 mg) was mixed with normal saline to produce 30 mL of study fluid. Each subject received two different doses, one on each side, applied randomly in a double-masked fashion. The end points included the maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle and tolerance to cutaneous electrical current in the femoral nerve distribution. Measurements were performed from baseline until quadriceps MVIC returned to 80% of baseline bilaterally. Results There were statistically significant dose responses in MVIC (0.09% / mg, SE = 0.03, 95% CI 0.04 to 0.14, p = 0.002) and tolerance to cutaneous current (?0.03 mA / mg, SE = 0.01, 95% CI ?0.04 to 0.02, p < 0.001), however, in the opposite direction than expected (the higher the dose, the lower the observed effect). This inverse relationship is biologically implausible, and most likely due to the limited sample size and the subjective nature of the measurement instruments. While peak effects occurred within 24 hours after block administration in 75% of cases (95% CI 43 to 93%), block duration usually lasted much longer: for bupivacaine doses above 40 mg, tolerance to cutaneous current did not return to within 20% above baseline until after 24 h in 100% of subjects (95% CI 56 to 100). MVIC did not consistently return to within 20% of baseline until after 24 hours in 90% of subjects (95% CI 54 to 100%). Motor block duration was not correlated with bupivacaine dose (0.06 h/mg, SE = 0.14, 95% CI ?0.27 to 0.39, p = 0.707). Conclusions The results of this investigation suggest that deposition of a liposomal bupivacaine formulation adjacent to the femoral nerve results in a partial sensory and motor block of more than 24 hours for the highest doses examined. However, the high variability of block magnitude among subjects and inverse relationship of dose and response magnitude attests to the need for a Phase 3 study with a far larger sample size, and these results should be viewed as suggestive, requiring confirmation in a future trial. PMID:24108252

Ilfeld, Brian M.; Malhotra, Nisha; Furnish, Timothy J.; Donohue, Michael C.; Madison, Sarah J.

2013-01-01

293

Dose tracking and dose auditing in a comprehensive computed tomography dose-reduction program.  

PubMed

Implementation of a comprehensive computed tomography (CT) radiation dose-reduction program is a complex undertaking, requiring an assessment of baseline doses, an understanding of dose-saving techniques, and an ongoing appraisal of results. We describe the role of dose tracking in planning and executing a dose-reduction program and discuss the use of the American College of Radiology CT Dose Index Registry at our institution. We review the basics of dose-related CT scan parameters, the components of the dose report, and the dose-reduction techniques, showing how an understanding of each technique is important in effective auditing of "outlier" doses identified by dose tracking. PMID:25129210

Duong, Phuong-Anh; Little, Brent P

2014-08-01

294

A Maximum Likelihood Approach to Estimating Correlation Functions  

NASA Astrophysics Data System (ADS)

We define a maximum likelihood (ML for short) estimator for the correlation function, ?, that uses the same pair counting observables (D, R, DD, DR, RR) as the standard Landy & Szalay (LS for short) estimator. The ML estimator outperforms the LS estimator in that it results in smaller measurement errors at any fixed random point density. Put another way, the ML estimator can reach the same precision as the LS estimator with a significantly smaller random point catalog. Moreover, these gains are achieved without significantly increasing the computational requirements for estimating ?. We quantify the relative improvement of the ML estimator over the LS estimator and discuss the regimes under which these improvements are most significant. We present a short guide on how to implement the ML estimator and emphasize that the code alterations required to switch from an LS to an ML estimator are minimal.

Baxter, Eric Jones; Rozo, Eduardo

2013-12-01

295

Enhanced Low Dose Rate Sensitivity at Ultra-Low Dose Rates  

NASA Technical Reports Server (NTRS)

We have presented results of ultra-low dose rate irradiations (< or = 10 mrad(Si)/s) for a variety of radiation hardened and commercial linear bipolar devices. We observed low dose rate enhancement factors exceeding 1.5 in several parts. The worst case of dose rate enhancement resulted in functional failures, which occurred after 10 and 60 krad(Si), for devices irradiated at 0.5 and 10 mrad(Si)/s, respectively. Devices fabricated with radiation hardened processes and designs also displayed dose rate enhancement at below 10 mrad(Si)/s. Furthermore, the data indicated that these devices have not reached the damage saturation point. Therefore the degradation will likely continue to increase with increasing total dose, and the low dose rate enhancement will further magnify. The cases presented here, in addition to previous examples, illustrate the significance and pervasiveness of low dose rate enhancement at dose rates lower than 10 mrad(Si). These results present further challenges for radiation hardness assurance of bipolar linear circuits, and raise the question of whether the current standard test dose rate is conservative enough to bound degradations due to ELDRS.

Chen, Dakai; Pease, Ronald; Forney, James; Carts, Martin; Phan, Anthony; Cox, Stephen; Kruckmeyer, Kriby; Burns, Sam; Albarian, Rafi; Holcombe, Bruce; Little, Bradley; Salzman, James; Chaumont, Geraldine; Duperray, Herve; Ouellet, Al; Buchner, Stephen; LaBel, Kenneth

2011-01-01

296

The pharmacokinetics, CNS pharmacodynamics and adverse event profile of brivaracetam after single increasing oral doses in healthy males  

PubMed Central

What is already known about this subject Brivaracetam is a new chemical entity structurally related to levetiracetam, displaying a markedly higher affinity for the binding site believed to be primarily involved in the antiepileptic effect of levetiracetam. Studies to evaluate the pharmacological profile of brivaracetam demonstrate an approximately 10-fold higher potency than levetiracetam as well as a higher efficacy in models of epilepsy. If translated into therapeutic effects in humans, this would mean a greater decrease in seizure frequency and a higher number of responders and seizure-free patients in refractory epileptic patients as seen with levetiracetam. What this study adds This article reports the results of the first in human study with brivaracetam. Its pharmacokinetics and adverse events profile after single administration are evaluated, together with the effect of food on the former. Aims The objective of the study was to evaluate the pharmacokinetics (and how they are affected by food), CNS pharmacodynamics and the adverse event profile of brivaracetam after single increasing doses. Methods Healthy males (n = 27, divided into three alternating panels of nine subjects) received two different single oral doses of brivaracetam (10–1400 mg) and one dose of placebo during three periods of a randomized, double-blind, placebo-controlled study. The effect of food on its pharmacokinetics was assessed using a standard two-way crossover design in a further eight subjects who received two single oral doses of brivaracetam (150 mg) in the fasting state and after a high fat meal. Results Adverse events, none of which were serious, were mostly CNS-related and included somnolence, dizziness, and decreased attention, alertness, and motor control. Their incidence, severity and duration were dose-related. The maximum tolerated dose was established to be 1000 mg. Severe somnolence lasting 1 day occurred in one subject following 1400 mg. Brivaracetam was rapidly absorbed under fasting conditions, with a median tmax of approximately 1 h. Cmax was dose-proportional from 10 to 1400 mg, whereas AUC deviated from dose linearity above 600 mg. A high-fat meal had no effect on AUC (point estimate 0.99, 90%CI: 0.92–1.07) but delayed tmax (3 h) and decreased Cmax (point estimate 0.72, 90%CI: 0.66–0.79). Conclusions Brivaracetam was well tolerated after increasing single doses that represent up to several times the expected therapeutic dose. Brivaracetam was found to have desirable pharmacokinetic properties. The most common adverse events were somnolence and dizziness. PMID:17223857

Sargentini-Maier, Maria Laura; Rolan, Paul; Connell, John; Tytgat, Dominique; Jacobs, Tom; Pigeolet, Etienne; Riethuisen, Jean-Michel; Stockis, Armel

2007-01-01

297

Higher than Physician's Desk Reference (US) doses on atypical antipsychotics.  

PubMed

The Physician's Desk Reference (PDR) was established to provide for the practicing of a complete listing of all medications with the FDA-approved labelling, including dosage recommendations. Perhaps in order to maximise individual usage of medications, pharmaceutical companies have frequently targeted lowest possible doses for FDA approval. However, many patients with a variety of illnesses due to resistance and/or multiple illnesses, may need higher than these dose ranges to maximise therapeutic response. In terms of regularly prescribed atypical antipsychotics released over the past 10 years, only risperidone initially obtained approval for a dose for psychosis (16 mg) higher than that suggested currently (maximum of 8 mg). The dose that was approved for mania was lower: a maximum of 6 mg. The others: respectfully, olanzapine (schizophrenia: 15 mg, mania: 20 mg), quetiapine (schizophrenia: 750 mg; mania: 800 mg), ziprasidone (schizophrenia and mania: 160 mg) and aripiprazole (schizophrenia and mania: 30 mg) obtained approvals for psychosis that may limit adverse events but, at the same time, limit benefits. Other data from various sources (double-blind trials, open-label trials, reviews and case reports) have found safety and/or efficacy for the following maximum doses: olanzapine (40 mg), quetiapine (1600 mg), ziprasidone (320 mg) and aripiprazole (75 mg). Reports above those doses are included, but either are insufficient in numbers or bring up questions on safety. In many situations, feared increase in adverse events were not magnified by use of higher doses. PMID:16011445

Goodnick, Paul J

2005-07-01

298

Influence of maximum bite force on jaw movement during gummy jelly mastication.  

PubMed

It is known that maximum bite force has various influences on chewing function; however, there have not been studies in which the relationships between maximum bite force and masticatory jaw movement have been clarified. The aim of this study was to investigate the effect of maximum bite force on masticatory jaw movement in subjects with normal occlusion. Thirty young adults (22 men and 8 women; mean age, 22.6 years) with good occlusion were divided into two groups based on whether they had a relatively high or low maximum bite force according to the median. The maximum bite force was determined according to the Dental Prescale System using pressure-sensitive sheets. Jaw movement during mastication of hard gummy jelly (each 5.5 g) on the preferred chewing side was recorded using a six degrees of freedom jaw movement recording system. The motion of the lower incisal point of the mandible was computed, and the mean values of 10 cycles (cycles 2-11) were calculated. A masticatory performance test was conducted using gummy jelly. Subjects with a lower maximum bite force showed increased maximum lateral amplitude, closing distance, width and closing angle; wider masticatory jaw movement; and significantly lower masticatory performance. However, no differences in the maximum vertical or maximum anteroposterior amplitudes were observed between the groups. Although other factors, such as individual morphology, may influence masticatory jaw movement, our results suggest that subjects with a lower maximum bite force show increased lateral jaw motion during mastication. PMID:24612273

Kuninori, T; Tomonari, H; Uehara, S; Kitashima, F; Yagi, T; Miyawaki, S

2014-05-01

299

Radiation Dose Estimates from  

E-print Network

Summary: Radiation Dose Estimates from Hanford Radioactive Material Releases to the Air and the Columbia River April 21,1994 TheTechnid Steering Panel of the Hanford - Environmental Dose Reconstruction than 40years, the U.S. Government made plutonium for nuclear weapons at the Hanford

300

Cancer chemoprevention by dietary chlorophylls: a 12,000-animal dose-dose matrix biomarker and tumor study.  

PubMed

Recent pilot studies found natural chlorophyll (Chl) to inhibit carcinogen uptake and tumorigenesis in rodent and fish models, and to alter uptake and biodistribution of trace (14)C-aflatoxin B1 in human volunteers. The present study extends these promising findings, using a dose-dose matrix design to examine Chl-mediated effects on dibenzo(def,p)chrysene (DBC)-induced DNA adduct formation, tumor incidence, tumor multiplicity, and changes in gene regulation in the trout. The dose-dose matrix design employed an initial 12,360 rainbow trout, which were treated with 0-4000ppm dietary Chl along with 0-225ppm DBC for up to 4weeks. Dietary DBC was found to induce dose-responsive changes in gene expression that were abolished by Chl co-treatment, whereas Chl alone had no effect on the same genes. Chl co-treatment provided a dose-responsive reduction in total DBC-DNA adducts without altering relative adduct intensities along the chromatographic profile. In animals receiving DBC alone, liver tumor incidence (as logit) and tumor multiplicity were linear in DBC dose (as log) up to their maximum-effect dose, and declined thereafter. Chl co-treatment substantially inhibited incidence and multiplicity at DBC doses up to their maximum-effect dose. These results show that Chl concentrations encountered in Chl-rich green vegetables can provide substantial cancer chemoprotection, and suggest that they do so by reducing carcinogen bioavailability. However, at DBC doses above the optima, Chl co-treatments failed to inhibit tumor incidence and significantly enhanced multiplicity. This finding questions the human relevance of chemoprevention studies carried out at high carcinogen doses that are not proven to lie within a linear, or at least monotonic, endpoint dose-response range. PMID:22079312

McQuistan, Tammie J; Simonich, Michael T; Pratt, M Margaret; Pereira, Cliff B; Hendricks, Jerry D; Dashwood, Roderick H; Williams, David E; Bailey, George S

2012-02-01

301

Decay heat and gamma dose-rate prediction capability in spent LWR fuel  

SciTech Connect

The ORIGEN2 code was established as a valid means to predict decay heat from LWR spent fuel assemblies for decay times up to 10,000 year. Calculational uncertainties ranged from 8.6% to a maximum of 16% at 2.5 years and 300 years cooling time, respectively. The calculational uncertainties at 2.5 years cooling time are supported by experiment. Major sources of uncertainty at the 2.5 year cooling time were identifed as irradiation history (5.7%) and nuclear data together with calculational methods (6.3%). The QAD shielding code was established as a valid means to predict interior and exterior gamma dose rates of spent LWR fuel assemblies. A calculational/measurement comparison was done on two assemblies with different irradiation histories and supports a 35% calculational uncertainty at the 1.8 and 3.0 year decay times studied. Uncertainties at longer times are expected to increase, but not significantly, due to an increased contribution from the actinides whose inventories are assigned a higher uncertainty. The uncertainty in decay heat rises to a maximum of 16% due to actinide uncertainties. A previous study was made of the neutron emission rate from a typical Turkey Point Unit 3, Region 4 spent fuel assembly at 5 years decay time. A conservative estimate of the neutron dose rate at the assembly surface was less than 0.5 rem/hr.

Neely, G J; Schmittroth, F

1982-08-01

302

40 CFR 94.107 - Determination of maximum test speed.  

Code of Federal Regulations, 2010 CFR

...false Determination of maximum test speed. 94.107 Section 94.107 Protection...107 Determination of maximum test speed. (a) Overview. This section specifies how to determine maximum test speed from a lug curve. This maximum...

2010-07-01

303

40 CFR 94.107 - Determination of maximum test speed.  

Code of Federal Regulations, 2011 CFR

...false Determination of maximum test speed. 94.107 Section 94.107 Protection...107 Determination of maximum test speed. (a) Overview. This section specifies how to determine maximum test speed from a lug curve. This maximum...

2011-07-01

304

Cell development obeys maximum Fisher information  

E-print Network

Eukaryotic cell development has been optimized by natural selection to obey maximal intracellular flux of messenger proteins. This, in turn, implies maximum Fisher information on angular position about a target nuclear pore complex (NPR). The cell is simply modeled as spherical, with cell membrane (CM) diameter 10 micron and concentric nuclear membrane (NM) diameter 6 micron. The NM contains about 3000 nuclear pore complexes (NPCs). Development requires messenger ligands to travel from the CM-NPC-DNA target binding sites. Ligands acquire negative charge by phosphorylation, passing through the cytoplasm over Newtonian trajectories toward positively charged NPCs (utilizing positive nuclear localization sequences). The CM-NPC channel obeys maximized mean protein flux F and Fisher information I at the NPC, with first-order delta I = 0 and approximate 2nd-order delta I = 0 stability to environmental perturbations. Many of its predictions are confirmed, including the dominance of protein pathways of from 1-4 proteins, a 4nm size for the EGFR protein and the approximate flux value F =10^16 proteins/m2-s. After entering the nucleus, each protein ultimately delivers its ligand information to a DNA target site with maximum probability, i.e. maximum Kullback-Liebler entropy HKL. In a smoothness limit HKL approaches IDNA/2, so that the total CM-NPC-DNA channel obeys maximum Fisher I. Thus maximum information approaches non-equilibrium, one condition for life.

B. R. Frieden; R. A. Gatenby

2014-04-29

305

Assessment of public doses due to a neutron calibration bunker.  

PubMed

In this work, the expected neutron and gamma doses in the populated areas outside the newly constructed neutron calibration bunker at the Atomic Energy Commission of Syria will be assessed using the Monte Carlo code MCNP-4C2. The results showed that the maximum ambient dose equivalent rate (neutrons and gammas) outside the bunker would not exceed 0.5 microSv h(-1), assuming an Am-Be neutron source of emission rate of 10(8) n s(-1). The neutron dose is approximately 10 times higher than the photon dose. Sky shine contributes by about 25-50% of the neutron dose and 7-27% of the gamma dose, depending on the location. The simulation uncertainty due to the possible variations in the simulation parameters has been given particular importance. PMID:19946121

Suman, H; Kharita, M H; Yousef, S

2010-03-01

306

A Dose–Response Study for I-125 Prostate Implants  

Microsoft Academic Search

Purpose: No dose–response study has ever been performed for I-125 prostate implants using modern techniques of implant evaluation and modern treatment outcome end points. The amount of activity per volume implanted was increased over time based on review of postimplant dosimetry. This resulted in different delivered dose levels. This study explores the relationship between dose, biochemical failure, and biopsy results.Materials

Richard G Stock; Nelson N Stone; Andrea Tabert; Christopher Iannuzzi; J. Keith DeWyngaert

1998-01-01

307

Maximum Aerodynamic Force on an Ascending Space Vehicle  

NASA Astrophysics Data System (ADS)

The March 2010 issue of The Physics Teacher includes a great article by Metz and Stinner on the kinematics and dynamics of a space shuttle launch. Within those pages is a brief mention of an event known in the language of the National Aeronautics and Space Administration (NASA) as "maximum dynamic pressure" (called simply "Max.AirPressure" in the article), where the combined effect of air density and the shuttles speed produce the greatest aerodynamic stress on the vehicle as it ascends through the atmosphere toward orbit. Official commentary during a launch2 refers to this point in the ascent with language such as "space shuttle main engines throttling back as vehicle enters area of maximum dynamic pressure" and occurs in a range between 45 and 60 s after launch. (In dealing with this stress, the space shuttles main engines reduce their thrust at approximately 45 s to reduce acceleration, and return to normal levels again some 15 s later as maximum dynamic pressure is traversed.) This paper presents an analysis, accessible to introductory-level students, that predicts the time of Max. AirPressure for a given ascending spacecraft.

Backman, Philip

2012-03-01

308

Accuracy and optimal timing of activity measurements in estimating the absorbed dose of radioiodine in the treatment of Graves' disease  

NASA Astrophysics Data System (ADS)

Calculation of the therapeutic activity of radioiodine 131I for individualized dosimetry in the treatment of Graves' disease requires an accurate estimate of the thyroid absorbed radiation dose based on a tracer activity administration of 131I. Common approaches (Marinelli-Quimby formula, MIRD algorithm) use, respectively, the effective half-life of radioiodine in the thyroid and the time-integrated activity. Many physicians perform one, two, or at most three tracer dose activity measurements at various times and calculate the required therapeutic activity by ad hoc methods. In this paper, we study the accuracy of estimates of four 'target variables': time-integrated activity coefficient, time of maximum activity, maximum activity, and effective half-life in the gland. Clinical data from 41 patients who underwent 131I therapy for Graves' disease at the University Hospital in Pisa, Italy, are used for analysis. The radioiodine kinetics are described using a nonlinear mixed-effects model. The distributions of the target variables in the patient population are characterized. Using minimum root mean squared error as the criterion, optimal 1-, 2-, and 3-point sampling schedules are determined for estimation of the target variables, and probabilistic bounds are given for the errors under the optimal times. An algorithm is developed for computing the optimal 1-, 2-, and 3-point sampling schedules for the target variables. This algorithm is implemented in a freely available software tool. Taking into consideration 131I effective half-life in the thyroid and measurement noise, the optimal 1-point time for time-integrated activity coefficient is a measurement 1 week following the tracer dose. Additional measurements give only a slight improvement in accuracy.

Merrill, S.; Horowitz, J.; Traino, A. C.; Chipkin, S. R.; Hollot, C. V.; Chait, Y.

2011-02-01

309

BENCHMARK DOSE TECHNICAL GUIDANCE DOCUMENT (EXTERNAL REVIEW DRAFT)  

EPA Science Inventory

The purpose of this document is to provide guidance for the Agency on the application of the benchmark dose approach in determining the point of departure (POD) for health effects data, whether a linear or nonlinear low dose extrapolation is used. The guidance includes discussion...

310

Low-Power Maximum Power Point Tracker with Digital Control for Thermophotovoltaic Generators  

E-print Network

This paper describes the design, optimization, and evaluation of the power electronics circuitry for a low-power portable thermophotovotaic (TPV) generator system. TPV system is based on a silicon micro-reactor design and ...

Pilawa, Robert

311

Maximum likelihood estimation of cascade point-process neural encoding models  

Microsoft Academic Search

Recent work has examined the estimation of models of stimulus-driven neural activity in which some linear filtering process is followed by a nonlinear, probabilistic spiking stage. We analyze the estimation of one such model for which this nonlinear step is implemented by a known parametric function; the assumption that this function is known speeds the estimation process considerably. We investigate

Liam Paninski

2004-01-01

312

A Fuzzy-Based Maximum Power Point Tracker for Body Mounted Solar Panels in LEO Satellites  

Microsoft Academic Search

Solar panels are the power subsystem components which provide satellite electrical power. Solar panels characteristics depend on environmental conditions (insolation level, temperature and etc.). In this paper, design and simulation of fuzzy-based MPPT for the body mounted solar panel in a LEO satellite are presented. To show how good the proposed technique is; we applied it into a real system.

M. Taherbaneh; M. B. Menhaj

2007-01-01

313

Evaluation of performance of photovoltaic system with maximum power point (MPP)  

Microsoft Academic Search

Performance of the photovoltaic system is highly influenced by the weather, especially the irradiation and the temperature. To simplify the design of solar generator power, a mathematical model and its validity of the solar cell are required. In this work, the value of the parameters in the mathematical model is obtained by the measurement of the I–V curve of the

Harsono Hadi; Shinobu Tokuda; Slamet Rahardjo

2003-01-01

314

Maximum stabilizer dimension for nonproduct states  

SciTech Connect

Composite quantum states can be classified by how they behave under local unitary transformations. Each quantum state has a stabilizer subgroup and a corresponding Lie algebra, the structure of which is a local unitary invariant. In this paper, we study the structure of the stabilizer subalgebra for n-qubit pure states, and find its maximum dimension to be n-1 for nonproduct states of three qubits and higher. The n-qubit Greenberger-Horne-Zeilinger state has a stabilizer subalgebra that achieves the maximum possible dimension for pure nonproduct states. The converse, however, is not true: We show examples of pure 4-qubit states that achieve the maximum nonproduct stabilizer dimension, but have stabilizer subalgebra structures different from that of the n-qubit GHZ state.

Walck, Scott N.; Lyons, David W. [Lebanon Valley College, Annville, Pennsylvania 17003 (United States)

2007-08-15

315

Maximum stabilizer dimension for nonproduct states  

E-print Network

Composite quantum states can be classified by how they behave under local unitary transformations. Each quantum state has a stabilizer subgroup and a corresponding Lie algebra, the structure of which is a local unitary invariant. In this paper, we study the structure of the stabilizer subalgebra for n-qubit pure states, and find its maximum dimension to be n-1 for nonproduct states of three qubits and higher. The n-qubit Greenberger-Horne-Zeilinger state has a stabilizer subalgebra that achieves the maximum possible dimension for pure nonproduct states. The converse, however, is not true: we show examples of pure 4-qubit states that achieve the maximum nonproduct stabilizer dimension, but have stabilizer subalgebra structures different from that of the n-qubit GHZ state.

Scott N. Walck; David W. Lyons

2007-06-12

316

Investigation of the spatial resolution of an online dose verification device  

SciTech Connect

Purpose: The aim of this work is to characterize a new online dose verification device, COMPASS transmission detector array (IBA Dosimetry, Schwarzenbruck, Germany). The array is composed of 1600 cylindrical ionization chambers of 3.8 mm diameter, separated by 6.5 mm center-to-center spacing, in a 40 x 40 arrangement. Methods: The line spread function (LSF) of a single ion chamber in the detector was measured with a narrow slit collimator for a 6 MV photon beam. The 0.25 x 10 mm{sup 2} slit was formed by two machined lead blocks. The LSF was obtained by laterally translating the detector in 0.25 mm steps underneath the slit over a range of 24 mm and taking a measurement at each step. This measurement was validated with Monte Carlo simulation using BEAMnrc and DOSXYZnrc. The presampling modulation transfer function (MTF), the Fourier transform of the line spread function, was determined and compared to calculated (Monte Carlo and analytical) MTFs. Two head-and-neck intensity modulated radiation therapy (IMRT) fields were measured using the device and were used to validate the LSF measurement. These fields were simulated with the BEAMnrc Monte Carlo model, and the Monte Carlo generated incident fluence was convolved with the 2D detector response function (derived from the measured LSF) to obtain calculated dose. The measured and calculated dose distributions were then quantitatively compared using {chi}-comparison criteria of 3% dose difference and 3 mm distance-to-agreement for in-field points (defined as those above the 10% maximum dose threshold). Results: The full width at half-maximum (FWHM) of the measured detector response for a single chamber is 4.3 mm, which is comparable to the chamber diameter of 3.8 mm. The pre-sampling MTF was calculated, and the resolution of one chamber was estimated as 0.25 lp/mm from the first zero crossing. For both examined IMRT fields, the {chi}-comparison between measured and calculated data show good agreement with 95.1% and 96.3% of in-field points below {chi} of 1.0 for fields 1 and 2, respectively (with an average {chi} of 0.29 for IMRT field 1 and 0.24 for IMRT field 2). Conclusions: The LSF for a new novel online detector has been measured at 6 MV using a narrow slit technique, and this measurement has been validated by Monte Carlo simulation. The detector response function derived from line spread function has been applied to recover measured IMRT fields. The results have shown that the device measures IMRT fields accurately within acceptable tolerance.

Asuni, G.; Rickey, D. W.; McCurdy, B. M. C. [Division of Medical Physics, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9 (Canada) and Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Division of Medical Physics, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9 (Canada); Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada) and Department of Radiology, University of Manitoba, Winnipeg, Manitoba R3A 1R9 (Canada)

2012-02-15

317

Safety, tolerability, and pharmacokinetics of eliglustat tartrate (Genz-112638) after single doses, multiple doses, and food in healthy volunteers.  

PubMed

Three phase 1 studies of eliglustat tartrate (Genz-112638), an oral inhibitor of glucosylceramide synthase under development for treating Gaucher disease type 1 (GD1), evaluated the safety, tolerability, and pharmacokinetics in healthy volunteers after escalating single doses (n = 99), escalating multiple doses (n = 36), and food (n = 24). Eliglustat tartrate was well tolerated at single doses ? 20 mg/kg and multiple doses ? 200 mg bid, with 50 mg bid producing plasma concentrations in the predicted therapeutic range. No serious adverse events occurred. Mild to moderate events of nausea, dizziness, and vomiting increased in frequency with escalating single and multiple doses. Single doses ? 10 mg/kg caused mild increases in electrocardiogram PR, QRS, and QT/QTc intervals. Single-dose pharmacokinetics showed dose linearity but not proportionality. Maximum plasma concentrations occurred at ~2 hours, followed by a monophasic decline with a ~6-hour terminal half-life. Unchanged drug in 8-hour urine collections was <1.5% of administered doses. Food did not significantly affect the rate or extent of absorption. Multiple-dose pharmacokinetics was nonlinear, showing higher than expected plasma drug concentrations. Steady state was reached ~60 hours after bid dosing. Higher drug exposure occurred in slower CYP2D6 metabolizers. Based on favorable results in healthy participants, a phase 2 trial of eliglustat tartrate was initiated in GD1 patients. PMID:20864621

Peterschmitt, M Judith; Burke, Amy; Blankstein, Larry; Smith, Sharon E; Puga, Ana Cristina; Kramer, William G; Harris, James A; Mathews, David; Bonate, Peter L

2011-05-01

318

Density estimation by maximum quantum entropy  

SciTech Connect

A new Bayesian method for non-parametric density estimation is proposed, based on a mathematical analogy to quantum statistical physics. The mathematical procedure is related to maximum entropy methods for inverse problems and image reconstruction. The information divergence enforces global smoothing toward default models, convexity, positivity, extensivity and normalization. The novel feature is the replacement of classical entropy by quantum entropy, so that local smoothing is enforced by constraints on differential operators. The linear response of the estimate is proportional to the covariance. The hyperparameters are estimated by type-II maximum likelihood (evidence). The method is demonstrated on textbook data sets.

Silver, R.N.; Wallstrom, T.; Martz, H.F.

1993-11-01

319

Entropy generation: Minimum inside and maximum outside  

NASA Astrophysics Data System (ADS)

The extremum of entropy generation is evaluated for both maximum and minimum cases using a thermodynamic approach which is usually applied in engineering to design energy transduction systems. A new result in the thermodynamic analysis of the entropy generation extremum theorem is proved by the engineering approach. It follows from the proof that the entropy generation results as a maximum when it is evaluated by the exterior surroundings of the system and a minimum when it is evaluated within the system. The Bernoulli equation is analyzed as an example in order to evaluate the internal and external dissipations, in accordance with the theoretical results obtained.

Lucia, Umberto

2014-02-01

320

Matching of DC motors to photovoltaic generators for maximum daily gross mechanical energy  

Microsoft Academic Search

The matching to solar-cell generators of both separately excited and series DC motors driving pumping loads is addressed. It is shown that the maximum gross mechanical power can be obtained at slightly higher voltages and slightly lower currents compared to the maximum electrical-power points on the solar-cell generator characteristics at different insolation levels. Guidelines for constructing the loci of the

M. M. Saied

1988-01-01

321

Comparison of organ dose and dose equivalent for human phantoms of CAM vs. MAX  

NASA Astrophysics Data System (ADS)

For the evaluation of organ dose and dose equivalent of astronauts on space shuttle and the International Space Station (ISS) missions, the CAMERA models of CAM (Computerized Anatomical Male) and CAF (Computerized Anatomical Female) of human tissue shielding have been implemented and used in radiation transport model calculations at NASA. One of new human geometry models to meet the “reference person” of International Commission on Radiological Protection (ICRP) is based on detailed Voxel (volumetric and pixel) phantom models denoted for male and female as MAX (Male Adult voXel) and FAX (Female Adult voXel), respectively. We compared the CAM model predictions of organ doses to those of MAX model, since the MAX model represents the male adult body with much higher fidelity than the CAM model currently used at NASA. Directional body-shielding mass was evaluated for over 1500 target points of MAX for specified organs considered to be sensitive to the induction of stochastic effects. Radiation exposures to solar particle event (SPE), trapped protons, and galactic cosmic ray (GCR) were assessed at the specific sites in the MAX phantom by coupling space radiation transport models with the relevant body-shielding mass. The development of multiple-point body-shielding distributions at each organ made it possible to estimate the mean and variance of organ doses at the specific organ. For the estimate of doses to the blood forming organs (BFOs), data on active marrow distributions in adult were used to weight the bone marrow sites over the human body. The discrete number of target points of MAX organs resulted in a reduced organ dose and dose equivalent compared to the results of CAM organs especially for SPE, and should be further investigated. Differences of effective doses between the two approaches were found to be small (<5%) for GCR.

Kim, Myung-Hee Y.; Qualls, Garry D.; Slaba, Tony C.; Cucinotta, Francis A.

2010-04-01

322

Correction of CT artifacts and its influence on Monte Carlo dose calculations  

SciTech Connect

Computed tomography (CT) images of patients having metallic implants or dental fillings exhibit severe streaking artifacts. These artifacts may disallow tumor and organ delineation and compromise dose calculation outcomes in radiotherapy. We used a sinogram interpolation metal streaking artifact correction algorithm on several phantoms of exact-known compositions and on a prostate patient with two hip prostheses. We compared original CT images and artifact-corrected images of both. To evaluate the effect of the artifact correction on dose calculations, we performed Monte Carlo dose calculation in the EGSnrc/DOSXYZnrc code. For the phantoms, we performed calculations in the exact geometry, in the original CT geometry and in the artifact-corrected geometry for photon and electron beams. The maximum errors in 6 MV photon beam dose calculation were found to exceed 25% in original CT images when the standard DOSXYZnrc/CTCREATE calibration is used but less than 2% in artifact-corrected images when an extended calibration is used. The extended calibration includes an extra calibration point for a metal. The patient dose volume histograms of a hypothetical target irradiated by five 18 MV photon beams in a hypothetical treatment differ significantly in the original CT geometry and in the artifact-corrected geometry. This was found to be mostly due to miss-assignment of tissue voxels to air due to metal artifacts. We also developed a simple Monte Carlo model for a CT scanner and we simulated the contribution of scatter and beam hardening to metal streaking artifacts. We found that whereas beam hardening has a minor effect on metal artifacts, scatter is an important cause of these artifacts.

Bazalova, Magdalena; Beaulieu, Luc; Palefsky, Steven; Verhaegen, Frank [Medical Physics Department, McGill University, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec, H3G1A4 (Canada); Department de Physique, de Genie Physique et d'Optique, Universite Laval, Quebec City, Quebec, G1K7P4 (Canada) and Department de Radio-Oncologie, Hotel Dieu de Quebec, Centre Hospitalier Universitaire de Quebec, Quebec City, Quebec, G1R2J6 (Canada); Medical Physics Department, McGill University, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec, H3G1A4 (Canada)

2007-06-15

323

Estimates of potential radiation doses from wristwatches containing tritium gas  

Microsoft Academic Search

Potential radiation doses were estimated for the United States population from normal distribution, use, repair, and disposal of wrist watches containing up to 200 mCi of tritium (H-3) gas in sealed glass tubes which function as self-luminous light sources. The maximum annual total-body dose was calculated to be 0.3 mrem during watch distribution. Watch wearers were estimated to receive annual

L. M. McDowell-Boyer; F. R. ODonnell

1978-01-01

324

Single and multiple dose pharmacokinetics of etizolam in healthy subjects  

Microsoft Academic Search

The pharmacokinetics of etizolam, a new thienodiazepine derivative, has been examined after single and multiple (0.5 mg tablet) (0.5 mg b.d for 1 week) oral therapeutic doses in healthy volunteers. The single-dose kinetic profile of etizolam suggested that absorption after oral dosage was reasonably rapid, the maximum plasma concentration (Cmax) being attained within 0.5–2 h in all subjects. The mean

C. Fracasso; S. Confalonieri; S. Garattini; S. Caccia

1991-01-01

325

Retrospective Monte Carlo dose calculations with limited beam weight information  

SciTech Connect

An important unresolved issue in outcomes analysis for lung complications is the effect of poor or completely lacking heterogeneity corrections in previously archived treatment plans. To estimate this effect, we developed a novel method based on Monte Carlo (MC) dose calculations which can be applied retrospectively to RTOG/AAPM-style archived treatment plans (ATP). We applied this method to 218 archived nonsmall cell lung cancer lung treatment plans that were originally calculated either without heterogeneity corrections or with primitive corrections. To retrospectively specify beam weights and wedges, beams were broken into Monte Carlo-generated beamlets, simulated using the VMC++ code, and mathematical optimization was used to match the archived water-based dose distributions. The derived beam weights (and any wedge effects) were then applied to Monte Carlo beamlets regenerated based on the patient computed tomography densities. Validation of the process was performed against five comparable lung treatment plans generated using a commercial convolution/superposition implementation. For the application here (normal lung, esophagus, and planning target volume dose distributions), the agreement was very good. Resulting MC and convolution/superposition values were similar when dose distributions without heterogeneity corrections or dose distributions with corrections were compared. When applied to the archived plans (218), the average absolute percent difference between water-based MC and water-based ATPs, for doses above 2.5% of the maximum dose was 1.8{+-}0.6%. The average absolute percent difference between heterogeneity-corrected MC and water-based ATPs increased to 3.1{+-}0.9%. The average absolute percent difference between the MC heterogeneity-corrected and the ATP heterogeneity-corrected dose distributions was 3.8{+-}1.6% (available in 132/218 archives). The entire dose-volume-histograms for lung, tumor, and esophagus from the different calculation methods, as well as specific dose metrics, were compared. The average difference in maximum lung dose between water-based ATPs and heterogeneity-corrected MC dose distributions was -1.0{+-}2.1 Gy. Potential errors in relying on primitive heterogeneity corrections are most evident from a comparison of maximum lung doses, for which the average MC heterogeneity-corrected values were 5.3{+-}2.8 Gy less than the ATP heterogeneity-corrected values. We have demonstrated that recalculation of archived dose distributions, without explicit information about beam weights or wedges, is feasible using beamlet-based optimization methods. The method provides heterogeneity-corrected dose data consistent with convolution-superposition calculations and is one feasible approach for improving dosimetric data for outcomes analyses.

Lindsay, Patricia E.; Naqa, Issam El; Hope, Andrew J.; Vicic, Milos; Cui Jing; Bradley, Jeffrey D.; Deasy, Joseph O. [Department of Radiation Oncology, Washington University School of Medicine, St Louis, Missouri 63110 (United States)

2007-01-15

326

Menu Plans: Maximum Nutrition for Minimum Cost.  

ERIC Educational Resources Information Center

Suggests that menu planning is the key to getting maximum nutrition in day care meals and snacks for minimum cost. Explores United States Department of Agriculture food pyramid guidelines for children and tips for planning menus and grocery shopping. Includes suggested meal patterns and portion sizes. (HTH)

Texas Child Care, 1995

1995-01-01

327

Learning Graphical Models by Maximum Entropy Relaxation  

E-print Network

.t. dE(, ) E, E H Maximize entropy subject to constraint that, for each subset E H, the marginal. Dual Problem: Maximize entropy h(r) -Er{log r} over all r M that satisfy linear moment con- straintsLearning Graphical Models by Maximum Entropy Relaxation Jason K. Johnson (Joint work with V

Willsky, Alan S.

328

Maximum Entropy MIMO Wireless Channel Models  

Microsoft Academic Search

In this contribution, models of wireless channels are derived from the maximum entropy principle, for several cases where only limited information about the propagation environment is available. First, ana- lytical models are derived for the cases where certain parameters (channel energy, average energy, spatial correlation matrix) are known deterministically. Frequently, these parameters are unknown (typically because the received energy or

Maxime Guillaud; Mérouane Debbah; Aris L. Moustakas

2006-01-01

329

Learning Markov Structure by Maximum Entropy Relaxation  

Microsoft Academic Search

We propose a new approach for learning a sparse graphical model approximation to a specified multivariate probability distri- bution (such as the empirical distribution of sample data). The selection of sparse graph structure arises naturally in our ap- proach through solution of a convex opti- mization problem, which differentiates our method from standard combinatorial ap- proaches. We seek the maximum

Jason K. Johnson; Venkat Chandrasekaran; Alan S. Willsky

2006-01-01

330

Maximum entropy methods for generating simulated rainfall  

E-print Network

Maximum entropy methods for generating simulated rainfall Julia Piantadosi Co-authors Phil Howlett entropy that matches an observed set of grade correlation coefficients. This problem is formulated as the maximization of a concave function on a convex polytope. · Under mild constraint qualifications we show

Borwein, Jonathan

331

Maximum entropy models for speech confidence estimation  

Microsoft Academic Search

In this work we implement a confidence estimation system based on a Naive Bayes classifier, by using the maximum entropy paradigm. The model takes information from various sources including a set of scores which have proved to be useful in confidence estimation tasks. Two different approaches are modeled. First a basic model which takes advantages of smoothing techniques used in

Claudio Estienne; Alberto Sanchís; Alfons Juan; Enrique Vidal

2008-01-01

332

Weak Scale From the Maximum Entropy Principle  

E-print Network

The theory of multiverse and wormholes suggests that the parameters of the Standard Model are fixed in such a way that the radiation of the $S^{3}$ universe at the final stage $S_{rad}$ becomes maximum, which we call the maximum entropy principle. Although it is difficult to confirm this principle generally, for a few parameters of the Standard Model, we can check whether $S_{rad}$ actually becomes maximum at the observed values. In this paper, we regard $S_{rad}$ at the final stage as a function of the weak scale ( the Higgs expectation value ) $v_{h}$, and show that it becomes maximum around $v_{h}={\\cal{O}}(300\\text{GeV})$ when the dimensionless couplings in the Standard Model, that is, the Higgs self coupling, the gauge couplings, and the Yukawa couplings are fixed. Roughly speaking, we find that the weak scale is given by \\begin{equation} v_{h}\\sim\\frac{T_{BBN}^{2}}{M_{pl}y_{e}^{5}},\

Yuta Hamada; Hikaru Kawai; Kiyoharu Kawana

2014-09-23

333

Muscle coordination of maximum-speed pedaling  

Microsoft Academic Search

A simulation based on a forward dynamical musculoskeletal model was computed from an optimal control algorithm to understand uni- and bi-articular muscle coordination of maximum-speed startup pedaling. The muscle excitations, pedal reaction forces, and crank and pedal kinematics of the simulation agreed with measurements from subjects. Over the crank cycle, uniarticular hip and knee extensor muscles provide 55% of the

Christine C. Raasch; Felix E. Zajac; Baoming Ma; William S. Levine

1997-01-01

334

20 CFR 229.48 - Family maximum.  

Code of Federal Regulations, 2010 CFR

...RAILROAD RETIREMENT ACT SOCIAL SECURITY OVERALL MINIMUM...defined. Under the Social Security Act, the...maximum used to adjust the social security overall minimum...Secretary of Health and Human Services on the...with the entitlement to more than one child's...

2010-04-01

335

: runout specimen max : maximum fatigue stress  

E-print Network

: runout specimen max : maximum fatigue stress fe,i : elastic limit strength of each specimen 750 uniaxial tensile fatigue stress. Interests in tensile fatigue strength and behaviour come from the fact.g. cantilever of bridge deck slab). Tensile Fatigue behaviour of UHPFRC Doctoral student: Tohru Makita

336

Maximum terminal velocity of relativistic rocket  

Microsoft Academic Search

The maximum terminal velocity problem of the classical propulsion is extended to a relativistic rocket assumed broken down into active mass, inert mass and gross payload. A fraction of the active mass is converted into energy shared between inert mass and active mass residual. Significant effects are considered. State and co-state equations are carried out to find the exhaust speed

G. Vulpetti

1985-01-01

337

Maximum Entropy Models for Named Entity Recognition  

Microsoft Academic Search

In this paper, we describe a system that applies maximum entropy (ME) models to the task of named entity recognition (NER). Starting with an annotated corpus and a set of features which are easily obtainable for almost any language, we first build a baseline NE recognizer which is then used to extract the named entities and their context information from

Oliver Bender; Franz Josef Och; Hermann Ney

338

Maximum Entropy Models for Named Entity Recoginition  

Microsoft Academic Search

In this paper, we describe a system that applies maximum entropy (ME) models to the task of named entity recognition (NER). Starting with an annotated corpus and a set of features which are easily obtainable for almost any language, we first build a baseline NE recognizer which is then used to extract the named entities and their context information from

O. Bender; F. J. Och; H. Ney

2003-01-01

339

PowerPoint Presentation  

Cancer.gov

36.8 33.8 43.9 32.7 16.1 23.6 23.8 25.5 0 5 10 15 20 25 30 35 40 45 50 Bx in Degassed Buffer Flash-frozen Bx Pre-Dose Deep Pre-Dose Shallow Post-Dose Shallow Validation and Fitness Testing of a Quantitative Immunoassay for HIF1? in Biopsy Specimens

340

Modelling lateral beam quality variations in pencil kernel based photon dose calculations  

NASA Astrophysics Data System (ADS)

Standard treatment machines for external radiotherapy are designed to yield flat dose distributions at a representative treatment depth. The common method to reach this goal is to use a flattening filter to decrease the fluence in the centre of the beam. A side effect of this filtering is that the average energy of the beam is generally lower at a distance from the central axis, a phenomenon commonly referred to as off-axis softening. The off-axis softening results in a relative change in beam quality that is almost independent of machine brand and model. Central axis dose calculations using pencil beam kernels show no drastic loss in accuracy when the off-axis beam quality variations are neglected. However, for dose calculated at off-axis positions the effect should be considered, otherwise errors of several per cent can be introduced. This work proposes a method to explicitly include the effect of off-axis softening in pencil kernel based photon dose calculations for arbitrary positions in a radiation field. Variations of pencil kernel values are modelled through a generic relation between half value layer (HVL) thickness and off-axis position for standard treatment machines. The pencil kernel integration for dose calculation is performed through sampling of energy fluence and beam quality in sectors of concentric circles around the calculation point. The method is fully based on generic data and therefore does not require any specific measurements for characterization of the off-axis softening effect, provided that the machine performance is in agreement with the assumed HVL variations. The model is verified versus profile measurements at different depths and through a model self-consistency check, using the dose calculation model to estimate HVL values at off-axis positions. A comparison between calculated and measured profiles at different depths showed a maximum relative error of 4% without explicit modelling of off-axis softening. The maximum relative error was reduced to 1% when the off-axis softening was accounted for in the calculations.

Nyholm, T.; Olofsson, J.; Ahnesjö, A.; Karlsson, M.

2006-08-01

341

Experimental design of bioassays for screening and low dose extrapolation  

SciTech Connect

Relatively high doses of chemicals generally are employed in animal bioassays to detect potential carcinogens with relatively small numbers of animals. The problem investigated here is the development of experimental designs which are effective for high to low dose extrapolation for tumor incidence as well as for screening (detecting) carcinogens. Several experimental designs are compared over a wide range of different dose response curves. Linear extrapolation is used below the experimental data range to establish an upper bound on carcinogenic risk at low doses. The goal is to find experimental designs which minimize the upper bound on low dose risk estimates (i.e., maximize the allowable dose for a given level of risk). The maximum tolerated dose (MTD) is employed for screening purposes. Among the designs investigated, experiments with doses at the MTD, 1/2 MTD, 1/4 MTD, and controls generally provide relatively good data for low dose extrapolation with relatively good power for detecting carcinogens. For this design, equal numbers of animals per dose level perform as well as unequal allocations.

Gaylor, D.W.; Chen, J.J.; Kodell, R.L.

1985-03-01

342

Theoretical Analysis of Maximum Flow Declination Rate versus Maximum Area Declination Rate in Phonation  

ERIC Educational Resources Information Center

Purpose: Maximum flow declination rate (MFDR) in the glottis is known to correlate strongly with vocal intensity in voicing. This declination, or negative slope on the glottal airflow waveform, is in part attributable to the maximum area declination rate (MADR) and in part to the overall inertia of the air column of the vocal tract (lungs to…

Titze, Ingo R.

2006-01-01

343

Disposition of firocoxib in equine plasma after an oral loading dose and a multiple dose regimen.  

PubMed

The objective of this study was to determine if a single loading dose (LD), 3× the label dose of firocoxib oral paste, followed by nine maintenance doses at the current label dose achieves and maintains near steady state concentrations. Six healthy, adult mares were administered 0.3mg/kg of firocoxib on Day 0, and 0.1 mg/kg 24 h later on Day 1, and at 24 h intervals from Day 2 to Day 9, for a total of 10 doses. Blood samples were collected throughout the study. The mean firocoxib maximum plasma concentration and standard deviation was 199±97 ng/mL, 175±44 ng/mL and 183±50 ng/mL after the LD, and first and last maintenance doses, respectively. The minimum mean concentration (C(min)) increased from 100±23 ng/mL after the LD to 132±38 ng/mL at Day 7. Then, the C(min) remained constant until Day 9. The average concentration at steady state (C(avg)) was 150±45 ng/mL, which compares well to the C(avg) (130±36 ng/mL) reported after multiple daily doses at 0.1 mg/kg. The administration of the single LD allowed achievement of the average steady state drug concentrations faster than a multi-dose regimen without a loading dose. After the LD, firocoxib at 0.1 mg/kg every 24 h was able to maintain a relatively constant average drug concentration which should produce less variability in onset of action and efficacy. PMID:24076125

Cox, S; Villarino, N; Sommardahl, C; Kvaternick, V; Zarabadipour, C; Siger, L; Yarbrough, J; Amicucci, A; Reed, K; Breeding, D; Doherty, T

2013-11-01

344

Effets pathogènes d'un faible débit de dose : la relation « dose effet »  

NASA Astrophysics Data System (ADS)

There is no evidence of pathogenic effects in human groups exposed to less than 100 mSv at low dose-rate. The attributed effects are therefore the result of extrapolations from higher doses. The validity of such extrapolations is discussed from the point of view of epidemiology as well as cellular and molecular biology. The Chernobyl accident resulted in large excess of thyroid cancers in children; it also raised the point that some actual sanitary effects among distressed populations might be a direct consequence of low doses. Studies under the control of UN have not confirmed this point identifying no dose-effect relationship and " severe socio-economic and psychological pressures… poverty, poor diet and living conditions, and lifestyle factors" as the main cause for depressed health. Some hypothesis are considered for explaining the dose-dependence and high prevalence of non-cancer causes of death among human groups exposed to more than 300 mSv. To cite this article: R. Masse, C. R. Physique 3 (2002) 1049-1058.

Masse, Roland

2002-10-01

345

Maximum-Flow Neural Network: A Novel Neural Network for the Maximum Flow Problem  

NASA Astrophysics Data System (ADS)

In advance of network communication society by the internet, the way how to send data fast with a little loss becomes an important transportation problem. A generalized maximum flow algorithm gives the best solution for the transportation problem that which route is appropriated to exchange data. Therefore, the importance of the maximum flow algorithm is growing more and more. In this paper, we propose a Maximum-Flow Neural Network (MF-NN) in which branch nonlinearity has a saturation characteristic and by which the maximum flow problem can be solved with analog high-speed parallel processing. That is, the proposed neural network for the maximum flow problem can be realized by a nonlinear resistive circuit where each connection weight between nodal neurons has a sigmodal or piece-wise linear function. The parallel hardware of the MF-NN will be easily implemented.

Sato, Masatoshi; Aomori, Hisashi; Tanaka, Mamoru

346

SPS antenna pointing control  

NASA Technical Reports Server (NTRS)

The pointing control of a microwave antenna of the Satellite Power System was investigated emphasizing: (1) the SPS antenna pointing error sensing method; (2) a rigid body pointing control design; and (3) approaches for modeling the flexible body characteristics of the solar collector. Accuracy requirements for the antenna pointing control consist of a mechanical pointing control accuracy of three arc-minutes and an electronic phased array pointing accuracy of three arc-seconds. Results based on the factors considered in current analysis, show that the three arc-minute overall pointing control accuracy can be achieved in practice.

Hung, J. C.

1980-01-01

347

Maximum likelihood estimation of turbulence spectrum parameters  

NASA Technical Reports Server (NTRS)

Estimation of the integral scale and intensity of a generic turbulence record is treated as a statistical problem of parameter estimation. Properties of parameter estimators and the method of maximum likelihood are reviewed. Likelihood equations are derived for estimation of the integral scale and intensity applicable to a general class of turbulence spectra that includes the von Karman and Dryden transverse and longitudinal spectra as special cases. The method is extended to include the Bullen transverse and longitudinal spectra. Coefficients of variation are given for maximum likelihood estimates of the integral scale and intensity of the von Karman spectra. Application of the method is illustrated by estimating the integral scale and intensity of an atmospheric turbulence vertical velocity record assumed to be governed by the von Karman transverse spectrum.

Mark, W. D.

1984-01-01

348

The maximum possible magnetocaloric ?T effect  

NASA Astrophysics Data System (ADS)

The current boom of research activity in magnetocaloric materials science is fuelled by the expectation that new advanced refrigerants may be found whose ?T will significantly surpass that of gadolinium (Gd) metal (2.6-2.9 K/T). Because of this expectation, the main effort in the field has been diverted from the important issues of refrigerator design to the routine characterization of magnetic materials. Estimating the maximum adiabatic temperature change that can be achieved in principle by applying a certain magnetic field, say 1 T, is a matter of priority. In this work the problem of maximum ?T is approached from general principles. According to the most optimistic estimates, ?T can never exceed ˜18 K/T, the more realistic upper limit lying somewhere in high single figures. We therefore deem it most unlikely that a refrigerant much better than Gd, in respect of the ?T value, will ever be found.

Zverev, V. I.; Tishin, A. M.; Kuz'min, M. D.

2010-02-01

349

MAXIMUM LIKELIHOOD ESTIMATION FOR SOCIAL NETWORK DYNAMICS  

PubMed Central

A model for network panel data is discussed, based on the assumption that the observed data are discrete observations of a continuous-time Markov process on the space of all directed graphs on a given node set, in which changes in tie variables are independent conditional on the current graph. The model for tie changes is parametric and designed for applications to social network analysis, where the network dynamics can be interpreted as being generated by choices made by the social actors represented by the nodes of the graph. An algorithm for calculating the Maximum Likelihood estimator is presented, based on data augmentation and stochastic approximation. An application to an evolving friendship network is given and a small simulation study is presented which suggests that for small data sets the Maximum Likelihood estimator is more efficient than the earlier proposed Method of Moments estimator.

Snijders, Tom A.B.; Koskinen, Johan; Schweinberger, Michael

2014-01-01

350

Study of maximum power tracking techniques and control of DC\\/DC converters for photovoltaic power system  

Microsoft Academic Search

As the electric power supplied by solar arrays depends on the insolation, temperature and array voltage, it is necessary to control the operating points to draw the maximum power of the solar array. The object of this paper is to investigate the maximum power tracking algorithms which were often used to compare the tracking efficiencies for the system operating under

Chihchiang Hua; Chihming Shen

1998-01-01

351

Maximum likelihood estimation in the 3-parameter Weibull distribution. A look through the generalized extreme-value distribution  

Microsoft Academic Search

The main contribution of this paper is to provide reasonable confidence intervals for maximum likelihood estimates of percentile points in dielectric breakdown voltage probability distributions. The Weibull distributions which include threshold values are often used in breakdown voltage distributions. In some breakdown voltage samples, there exist cases in which the maximum likelihood estimates of all the three Weibull parameters diverge;

H. Hirose

1996-01-01

352

Maximum likelihood estimation in pooled sample tests  

NASA Astrophysics Data System (ADS)

Pooled sample tests, firstly used on the classification problem (identifying all individuals with some characteristic), may also be applied to estimate the prevalence rate. Moreover, the pooled sample methods may attain greater efficiency when applied to estimate some prevalence rate, since it is no longer necessary to perform any individual test. We develop a maximum likelihood computational algorithm for the prevalence rate estimation, and we analyze its performance.

Martins, João Paulo; Felgueiras, Miguel; Santos, Rui

2014-10-01

353

Maximum Bounded Rooted-Tree Packing Problem  

E-print Network

Given a graph and a root, the Maximum Bounded Rooted-Tree Packing (MBRTP) problem aims at finding K rooted-trees that span the largest subset of vertices, when each vertex has a limited outdegree. This problem is motivated by peer-to-peer streaming overlays in under-provisioned systems. We prove that the MBRTP problem is NP-complete. We present two polynomial-time algorithms that computes an optimal solution on complete graphs and trees respectively.

Kerivin, Herve; Simon, Gwendal; Zhou, Fen

2011-01-01

354

Maximum likelihood identification using an array processor  

NASA Technical Reports Server (NTRS)

Maximum likelihood estimation (MLE) is a method used to calculate the parameters of a dynamic system. It can be applied to a large class of problems and has good statistical properties. The main disadvantage of the MLE method is the amount of computation required. This paper describes how the computation time can be reduced significantly by using an array processor. The estimation of the parameters of a dynamic model of the Space Station is used as an example to evaluate the method.

Sridhar, Banavar; Aubrun, Jean-Noel

1987-01-01

355

Polyenes with maximum HOMO–LUMO gap  

Microsoft Academic Search

On the basis of a variable neighbourhood search with the AutoGraphiX software, it is conjectured that for even numbers of atoms the fully conjugated acyclic ? system of maximum HOMO–LUMO gap is a `comb' in which each vertex of a backbone carries a single pendant edge. Chemically, this represents CnH3n\\/2+2, an ?,?-diene with methylene groups attached at all intermediate positions.

P. W. Fowler; P. Hansen; G. Caporossi; A. Soncini

2001-01-01

356

Maximum Likelihood Based Quantum Set Separation  

E-print Network

In this paper we introduce a method, which is used for set separation based on quantum computation. In case of no a-priori knowledge about the source signal distribution, it is a challenging task to find an optimal decision rule which could be implemented in the separating algorithm. We lean on the Maximum Likelihood approach and build a bridge between this method and quantum counting. The proposed method is also able to distinguish between disjunct sets and intersection sets.

Sándor Imre; Ferenc Balázs

2004-02-12

357

Maximum entropy production - Full steam ahead  

NASA Astrophysics Data System (ADS)

The application of a principle of Maximum Entropy Production (MEP, or less ambiguously MaxEP) to planetary climate is discussed. This idea suggests that if sufficiently free of dynamical constraints, the atmospheric and oceanic heat flows across a planet may conspire to maximize the generation of mechanical work, or entropy. Thermodynamic and information-theoretic aspects of this idea are discussed. These issues are also discussed in the context of dust devils, convective vortices found in strongly-heated desert areas.

Lorenz, Ralph D.

2012-05-01

358

Tissue Radiation Response with Maximum Tsallis Entropy  

SciTech Connect

The expression of survival factors for radiation damaged cells is currently based on probabilistic assumptions and experimentally fitted for each tumor, radiation, and conditions. Here, we show how the simplest of these radiobiological models can be derived from the maximum entropy principle of the classical Boltzmann-Gibbs expression. We extend this derivation using the Tsallis entropy and a cutoff hypothesis, motivated by clinical observations. The obtained expression shows a remarkable agreement with the experimental data found in the literature.

Sotolongo-Grau, O.; Rodriguez-Perez, D.; Antoranz, J. C.; Sotolongo-Costa, Oscar [UNED, Departamento de Fisica Matematica y de Fluidos, 28040 Madrid (Spain); UNED, Departamento de Fisica Matematica y de Fluidos, 28040 Madrid (Spain) and University of Havana, Catedra de Sistemas Complejos Henri Poincare, Havana 10400 (Cuba); University of Havana, Catedra de Sistemas Complejos Henri Poincare, Havana 10400 (Cuba)

2010-10-08

359

FIS/ANFIS Based Optimal Control for Maximum Power Extraction in Variable-speed Wind Energy Conversion System  

NASA Astrophysics Data System (ADS)

An optimal control for maximizing extraction of power in variable-speed wind energy conversion system is presented. Intelligent gradient detection by fuzzy inference system (FIS) in maximum power point tracking control is proposed to achieve power curve operating near optimal point. Speed rotor reference can be adjusted by maximum power point tracking fuzzy controller (MPPTFC) such that the turbine operates around maximum power. Power curve model can be modelled by using adaptive neuro fuzzy inference system (ANFIS). It is required to simply well estimate just a few number of maximum power points corresponding to optimum generator rotor speed under varying wind speed, implying its training can be done with less effort. Using the trained fuzzy model, some estimated maximum power points as well as their corresponding generator rotor speed and wind speed are determined, from which a linear wind speed feedback controller (LWSFC) capable of producing optimum generator speed can be obtained. Applied to a squirrel-cage induction generator based wind energy conversion system, MPPTFC and LWSFC could maximize extraction of the wind energy, verified by a power coefficient stay at its maximum almost all the time and an actual power line close to a maximum power efficiency line reference.

Nadhir, Ahmad; Naba, Agus; Hiyama, Takashi

360

75 FR 77010 - Nextera Energy Point Beach, LLC; Point Beach Nuclear Plant, Units 1 and 2, Draft Environmental...  

Federal Register 2010, 2011, 2012, 2013

...increase the maximum thermal power at the Point Beach Nuclear Plant (PBNP), Units 1 and...One Light-Water-Cooled Nuclear Power Reactor. Therefore, there...Evaluating Design Basis Accidents at Nuclear Power Reactors. The analyses...

2010-12-10

361

Targeted Maximum Likelihood Based Causal Inference: Part I  

PubMed Central

Given causal graph assumptions, intervention-specific counterfactual distributions of the data can be defined by the so called G-computation formula, which is obtained by carrying out these interventions on the likelihood of the data factorized according to the causal graph. The obtained G-computation formula represents the counterfactual distribution the data would have had if this intervention would have been enforced on the system generating the data. A causal effect of interest can now be defined as some difference between these counterfactual distributions indexed by different interventions. For example, the interventions can represent static treatment regimens or individualized treatment rules that assign treatment in response to time-dependent covariates, and the causal effects could be defined in terms of features of the mean of the treatment-regimen specific counterfactual outcome of interest as a function of the corresponding treatment regimens. Such features could be defined nonparametrically in terms of so called (nonparametric) marginal structural models for static or individualized treatment rules, whose parameters can be thought of as (smooth) summary measures of differences between the treatment regimen specific counterfactual distributions. In this article, we develop a particular targeted maximum likelihood estimator of causal effects of multiple time point interventions. This involves the use of loss-based super-learning to obtain an initial estimate of the unknown factors of the G-computation formula, and subsequently, applying a target-parameter specific optimal fluctuation function (least favorable parametric submodel) to each estimated factor, estimating the fluctuation parameter(s) with maximum likelihood estimation, and iterating this updating step of the initial factor till convergence. This iterative targeted maximum likelihood updating step makes the resulting estimator of the causal effect double robust in the sense that it is consistent if either the initial estimator is consistent, or the estimator of the optimal fluctuation function is consistent. The optimal fluctuation function is correctly specified if the conditional distributions of the nodes in the causal graph one intervenes upon are correctly specified. The latter conditional distributions often comprise the so called treatment and censoring mechanism. Selection among different targeted maximum likelihood estimators (e.g., indexed by different initial estimators) can be based on loss-based cross-validation such as likelihood based cross-validation or cross-validation based on another appropriate loss function for the distribution of the data. Some specific loss functions are mentioned in this article. Subsequently, a variety of interesting observations about this targeted maximum likelihood estimation procedure are made. This article provides the basis for the subsequent companion Part II-article in which concrete demonstrations for the implementation of the targeted MLE in complex causal effect estimation problems are provided. PMID:20737021

van der Laan, Mark J.

2010-01-01

362

Maximum a posteriori resampling of noisy, spatially correlated data  

NASA Astrophysics Data System (ADS)

In any geologic application, noisy data are sources of consternation for researchers, inhibiting interpretability and marring images with unsightly and unrealistic artifacts. Filtering is the typical solution to dealing with noisy data. However, filtering commonly suffers from ad hoc (i.e., uncalibrated, ungoverned) application. We present here an alternative to filtering: a newly developed method for correcting noise in data by finding the "best" value given available information. The motivating rationale is that data points that are close to each other in space cannot differ by "too much," where "too much" is governed by the field covariance. Data with large uncertainties will frequently violate this condition and therefore ought to be corrected, or "resampled." Our solution for resampling is determined by the maximum of the a posteriori density function defined by the intersection of (1) the data error probability density function (pdf) and (2) the conditional pdf, determined by the geostatistical kriging algorithm applied to proximal data values. A maximum a posteriori solution can be computed sequentially going through all the data, but the solution depends on the order in which the data are examined. We approximate the global a posteriori solution by randomizing this order and taking the average. A test with a synthetic data set sampled from a known field demonstrates quantitatively and qualitatively the improvement provided by the maximum a posteriori resampling algorithm. The method is also applied to three marine geology/geophysics data examples, demonstrating the viability of the method for diverse applications: (1) three generations of bathymetric data on the New Jersey shelf with disparate data uncertainties; (2) mean grain size data from the Adriatic Sea, which is a combination of both analytic (low uncertainty) and word-based (higher uncertainty) sources; and (3) side-scan backscatter data from the Martha's Vineyard Coastal Observatory which are, as is typical for such data, affected by speckle noise. Compared to filtering, maximum a posteriori resampling provides an objective and optimal method for reducing noise, and better preservation of the statistical properties of the sampled field. The primary disadvantage is that maximum a posteriori resampling is a computationally expensive procedure.

Goff, John A.; Jenkins, Chris; Calder, Brian

2006-08-01

363

EPR dose reconstruction for bone-seeking 90Sr.  

PubMed

The results of the EPR dose reconstruction in calcified tissues of dog injected with 90Sr are presented. It has been established that there is no essential difference in the values of doses absorbed in tooth tissues of teeth in symmetric positions in the mouth, whereas a significant difference occurs in the values of absorbed doses in teeth in non-symmetric positions. In the case of 90Sr internal exposure the dose reconstruction in crown dentine plays an important role. It has been found that its quantity is close to the dose in diaphyseal cortical bone of the femur, dose at the endosteal bone surface and in femural fatty marrow. The fact that these values exceed doses absorbed in tooth enamel points out the predominant contribution of internal exposure. The highest absorbed doses have been observed in metaphyseal trabecular femur bones, tooth alveolar bone walls, and cortical and trabecular vertebra that can be considered as suitable candidates for biomarkers of internal 90Sr exposure for post-mortal autopsy. The satisfactory correlation has been found between the doses reconstructed in calcified dog tissues and the doses measured by EPR in alanine dosimeters fixed in (or nearby) the sites of autopsy of bones/teeth. The experiments provide support for the view that EPR retrospective dosimetry with calcified tissues for internal exposure is unique in providing useful information on the doses obtained. PMID:10376327

Ignatiev, E A; Lyubashevskii, N M; Shishkina, E A; Romanyukha, A A

1999-08-01

364

Exenatide dosing in alpacas.  

PubMed

In order to investigate whether exenatide could be used to stimulate glucose clearance and insulin secretion in alpacas without causing colic signs, six healthy adult alpacas were injected once a day with increasing subcutaneous doses. A follow-up intravenous glucose injection was given to induce hyperglycemia, and serial blood samples were collected to measure plasma concentrations of glucose, insulin, triglycerides, beta-hydroxybutyrate, and nonesterified fatty acids. The exenatide doses used were saline control (no drug), and 0.02, 0.05, or 0.1 mcg/kg injected subcutaneously. Alpacas had significantly lower plasma glucose concentrations and higher insulin concentrations on all treatment days compared with the control day, but the increase in insulin was significantly greater and lasted significantly longer when the alpacas received the two higher dosages. Two of the alpacas developed mild colic signs at the 0.05 mcg/kg dose and were not evaluated at the highest dose. Based on these findings, the 0.05 mcg/kg dose appears to offer the greatest stimulation of insulin secretion and glucose clearance without excessive risk or severity of complications. PMID:24479825

Cebra, C K; Smith, C C; Stang, B V; Tornquist, S J

2014-08-01

365

Motion as a perturbation: Measurement-guided dose estimates to moving patient voxels during modulated arc deliveries  

SciTech Connect

Purpose: To present a framework for measurement-guided VMAT dose reconstruction to moving patient voxels from a known motion kernel and the static phantom data, and to validate this perturbation-based approach with the proof-of-principle experiments. Methods: As described previously, the VMAT 3D dose to a static patient can be estimated by applying a phantom measurement-guided perturbation to the treatment planning system (TPS)-calculated dose grid. The fraction dose to any voxel in the presence of motion, assuming the motion kernel is known, can be derived in a similar fashion by applying a measurement-guided motion perturbation. The dose to the diodes in a helical phantom is recorded at 50 ms intervals and is transformed into a series of time-resolved high-density volumetric dose grids. A moving voxel is propagated through this 4D dose space and the fraction dose to that voxel in the phantom is accumulated. The ratio of this motion-perturbed, reconstructed dose to the TPS dose in the phantom serves as a perturbation factor, applied to the TPS fraction dose to the similarly situated voxel in the patient. This approach was validated by the ion chamber and film measurements on four phantoms of different shape and structure: homogeneous and inhomogeneous cylinders, a homogeneous cube, and an anthropomorphic thoracic phantom. A 2D motion stage was used to simulate the motion. The stage position was synchronized with the beam start time with the respiratory gating simulator. The motion patterns were designed such that the motion speed was in the upper range of the expected tumor motion (1-1.4 cm/s) and the range exceeded the normally observed limits (up to 5.7 cm). The conformal arc plans for X or Y motion (in the IEC 61217 coordinate system) consisted of manually created narrow (3 cm) rectangular strips moving in-phase (tracking) or phase-shifted by 90 Degree-Sign (crossing) with respect to the phantom motion. The XY motion was tested with the computer-derived VMAT MLC sequences. For all phantoms and plans, time-resolved (10 Hz) ion chamber dose was collected. In addition, coronal (XY) films were exposed in the cube phantom to a VMAT beam with two different starting phases, and compared to the reconstructed motion-perturbed dose planes. Results: For the X or Y motions with the moving strip and geometrical phantoms, the maximum difference between perturbation-reconstructed and ion chamber doses did not exceed 1.9%, and the average for any motion pattern/starting phase did not exceed 1.3%. For the VMAT plans on the cubic and thoracic phantoms, one point exhibited a 3.5% error, while the remaining five were all within 1.1%. Across all the measurements (N = 22), the average disagreement was 0.5 {+-} 1.3% (1 SD). The films exhibited {gamma}(3%/3 mm) passing rates {>=}90%. Conclusions: The dose to an arbitrary moving voxel in a patient can be estimated with acceptable accuracy for a VMAT delivery, by performing a single QA measurement with a cylindrical phantom and applying two consecutive perturbations to the TPS-calculated patient dose. The first one accounts for the differences between the planned and delivered static doses, while the second one corrects for the motion.

Feygelman, Vladimir; Zhang, Geoffrey; Hunt, Dylan; Opp, Daniel [Department of Radiation Oncology, Moffitt Cancer Center, Tampa, Florida 33612 (United States); Stambaugh, Cassandra [Department of Physics, University of South Florida, Tampa, Florida 33612 (United States); Wolf, Theresa K. [Live Oak Technologies LLC, Kirkwood, Missouri 63122 (United States); Nelms, Benjamin E. [Canis Lupus LLC, Merrimac, Wisconsin 53561 (United States)

2013-02-15

366

33 CFR 183.35 - Maximum weight capacity: Outboard boats.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Maximum weight capacity: Outboard boats. 183.35 ...EQUIPMENT Safe Loading § 183.35 Maximum weight capacity: Outboard boats. (a) The maximum weight capacity marked on a boat that is...

2010-07-01

367

33 CFR 183.35 - Maximum weight capacity: Outboard boats.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Maximum weight capacity: Outboard boats. 183.35 ...EQUIPMENT Safe Loading § 183.35 Maximum weight capacity: Outboard boats. (a) The maximum weight capacity marked on a boat that is...

2013-07-01

368

33 CFR 183.35 - Maximum weight capacity: Outboard boats.  

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 false Maximum weight capacity: Outboard boats. 183.35 ...EQUIPMENT Safe Loading § 183.35 Maximum weight capacity: Outboard boats. (a) The maximum weight capacity marked on a boat that is...

2011-07-01

369

33 CFR 183.35 - Maximum weight capacity: Outboard boats.  

...2014-07-01 2014-07-01 false Maximum weight capacity: Outboard boats. 183.35 ...EQUIPMENT Safe Loading § 183.35 Maximum weight capacity: Outboard boats. (a) The maximum weight capacity marked on a boat that is...

2014-07-01

370

33 CFR 183.35 - Maximum weight capacity: Outboard boats.  

Code of Federal Regulations, 2012 CFR

...2012-07-01 2012-07-01 false Maximum weight capacity: Outboard boats. 183.35 ...EQUIPMENT Safe Loading § 183.35 Maximum weight capacity: Outboard boats. (a) The maximum weight capacity marked on a boat that is...

2012-07-01

371

49 CFR 230.24 - Maximum allowable stress.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 false Maximum allowable stress. 230.24 Section 230.24 Transportation...STANDARDS Boilers and Appurtenances Allowable Stress § 230.24 Maximum allowable stress. (a) Maximum allowable stress value....

2011-10-01

372

49 CFR 230.24 - Maximum allowable stress.  

Code of Federal Regulations, 2012 CFR

... 2012-10-01 false Maximum allowable stress. 230.24 Section 230.24 Transportation...STANDARDS Boilers and Appurtenances Allowable Stress § 230.24 Maximum allowable stress. (a) Maximum allowable stress value....

2012-10-01

373

49 CFR 230.24 - Maximum allowable stress.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false Maximum allowable stress. 230.24 Section 230.24 Transportation...STANDARDS Boilers and Appurtenances Allowable Stress § 230.24 Maximum allowable stress. (a) Maximum allowable stress value....

2010-10-01

374

49 CFR 230.24 - Maximum allowable stress.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 false Maximum allowable stress. 230.24 Section 230.24 Transportation...STANDARDS Boilers and Appurtenances Allowable Stress § 230.24 Maximum allowable stress. (a) Maximum allowable stress value....

2013-10-01

375

40 CFR 141.13 - Maximum contaminant levels for turbidity.  

Code of Federal Regulations, 2013 CFR

... false Maximum contaminant levels for turbidity. 141.13 Section 141.13 Protection...141.13 Maximum contaminant levels for turbidity. The maximum contaminant levels for turbidity are applicable to both community...

2013-07-01

376

40 CFR 141.13 - Maximum contaminant levels for turbidity.  

Code of Federal Regulations, 2012 CFR

... false Maximum contaminant levels for turbidity. 141.13 Section 141.13 Protection...141.13 Maximum contaminant levels for turbidity. The maximum contaminant levels for turbidity are applicable to both community...

2012-07-01

377

40 CFR 141.13 - Maximum contaminant levels for turbidity.  

... false Maximum contaminant levels for turbidity. 141.13 Section 141.13 Protection...141.13 Maximum contaminant levels for turbidity. The maximum contaminant levels for turbidity are applicable to both community...

2014-07-01

378

40 CFR 141.13 - Maximum contaminant levels for turbidity.  

Code of Federal Regulations, 2010 CFR

... false Maximum contaminant levels for turbidity. 141.13 Section 141.13 Protection...141.13 Maximum contaminant levels for turbidity. The maximum contaminant levels for turbidity are applicable to both community...

2010-07-01

379

40 CFR 141.13 - Maximum contaminant levels for turbidity.  

Code of Federal Regulations, 2011 CFR

... false Maximum contaminant levels for turbidity. 141.13 Section 141.13 Protection...141.13 Maximum contaminant levels for turbidity. The maximum contaminant levels for turbidity are applicable to both community...

2011-07-01

380

14 CFR 25.1505 - Maximum operating limit speed.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Maximum operating limit speed. 25.1505 Section 25.1505 Aeronautics...Limitations § 25.1505 Maximum operating limit speed. The maximum operating limit speed (V MO /M MO airspeed or Mach...

2010-01-01

381

14 CFR 25.1505 - Maximum operating limit speed.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Maximum operating limit speed. 25.1505 Section 25.1505 Aeronautics...Limitations § 25.1505 Maximum operating limit speed. The maximum operating limit speed (V MO /M MO airspeed or Mach...

2011-01-01

382

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2011-10-01

383

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2012-10-01

384

49 CFR 230.27 - Maximum shearing strength of rivets.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Maximum shearing strength of rivets. 230.27 Section 230...STANDARDS Boilers and Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing...

2013-10-01

385

A comparison of minimum detectable and proposed maximum allowable soil concentration cleanup levels for selected radionuclides  

Microsoft Academic Search

Regulations on the release of a radioactively contaminated site for unrestricted use are currently being established by the Environmental Protection Agency. The effective dose equivalent rate limit for the reasonably maximally exposed individual was proposed at 0.15 mSv y⁻¹. The purpose of this study is to investigate whether or not maximum allowable soil concentrations of common radionuclides corresponding to 0.15

J. L. Wood; R. R. Benke; S. M. Rohrer; K. J. Kearfott

1999-01-01

386

Digital tomosynthesis mammography using a parallel maximum-likelihood reconstruction method  

Microsoft Academic Search

A parallel reconstruction method, based on an iterative maximum likelihood (ML) algorithm, is developed to provide fast reconstruction for digital tomosynthesis mammography. Tomosynthesis mammography acquires 11 low-dose projections of a breast by moving an x-ray tube over a 50° angular range. In parallel reconstruction, each projection is divided into multiple segments along the chest-to-nipple direction. Using the 11 projections, segments

Tao Wu; Juemin Zhang; Richard Moore; Elizabeth Rafferty; Daniel Kopans; Waleed Meleis; David Kaeli

2004-01-01

387

Test images for the maximum entropy image restoration method  

NASA Technical Reports Server (NTRS)

One of the major activities of any experimentalist is data analysis and reduction. In solar physics, remote observations are made of the sun in a variety of wavelengths and circumstances. In no case is the data collected free from the influence of the design and operation of the data gathering instrument as well as the ever present problem of noise. The presence of significant noise invalidates the simple inversion procedure regardless of the range of known correlation functions. The Maximum Entropy Method (MEM) attempts to perform this inversion by making minimal assumptions about the data. To provide a means of testing the MEM and characterizing its sensitivity to noise, choice of point spread function, type of data, etc., one would like to have test images of known characteristics that can represent the type of data being analyzed. A means of reconstructing these images is presented.

Mackey, James E.

1990-01-01

388

Maximum Likelihood Estimation (MLE) of students' understanding of vector subtraction  

NASA Astrophysics Data System (ADS)

In this paper, we report on the impact that slight changes in question format have on student response to one-dimensional vector subtraction tasks. We use Maximum Likelihood Estimation (MLE) analysis to analyze students' responses on six very similar questions which vary in context (physics or mathematics), vector alignment (both pointing to the right or opposed), and operation (left-right subtraction or right-left subtraction). Responses on all questions are generally correct and do not vary by instructional week or even by course. Context and specific operation do not show significant differences. Vector alignment is significantly different, indicating that perception or heuristic thinking is a bigger cause of failure than conceptual deficit. The emphasis in this paper is an introduction to likelihood estimation.

Wang, Tianren; Sayre, Eleanor C.

2010-10-01

389

Comparison of 2D and 3D Imaging and Treatment Planning for Postoperative Vaginal Apex High-Dose Rate Brachytherapy for Endometrial Cancer  

SciTech Connect

Purpose: To evaluate bladder and rectal doses using two-dimensional (2D) and 3D treatment planning for vaginal cuff high-dose rate (HDR) in endometrial cancer. Methods and Materials: Ninety-one consecutive patients treated between 2000 and 2007 were evaluated. Seventy-one and 20 patients underwent 2D and 3D planning, respectively. Each patient received six fractions prescribed at 0.5 cm to the superior 3 cm of the vagina. International Commission on Radiation Units and Measurements (ICRU) doses were calculated for 2D patients. Maximum and 2-cc doses were calculated for 3D patients. Organ doses were normalized to prescription dose. Results: Bladder maximum doses were 178% of ICRU doses (p < 0.0001). Two-cubic centimeter doses were no different than ICRU doses (p = 0.22). Two-cubic centimeter doses were 59% of maximum doses (p < 0.0001). Rectal maximum doses were 137% of ICRU doses (p < 0.0001). Two-cubic centimeter doses were 87% of ICRU doses (p < 0.0001). Two-cubic centimeter doses were 64% of maximum doses (p < 0.0001). Using the first 1, 2, 3, 4 or 5 fractions, we predicted the final bladder dose to within 10% for 44%, 59%, 83%, 82%, and 89% of patients by using the ICRU dose, and for 45%, 55%, 80%, 85%, and 85% of patients by using the maximum dose, and for 37%, 68%, 79%, 79%, and 84% of patients by using the 2-cc dose. Using the first 1, 2, 3, 4 or 5 fractions, we predicted the final rectal dose to within 10% for 100%, 100%, 100%, 100%, and 100% of patients by using the ICRU dose, and for 60%, 65%, 70%, 75%, and 75% of patients by using the maximum dose, and for 68%, 95%, 84%, 84%, and 84% of patients by using the 2-cc dose. Conclusions: Doses to organs at risk vary depending on the calculation method. In some cases, final dose accuracy appears to plateau after the third fraction, indicating that simulation and planning may not be necessary in all fractions. A clinically relevant level of accuracy should be determined and further research conducted to address this issue.

Russo, James K. [Department of Radiation Oncology, Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina (United States); Armeson, Kent E. [Division of Biostatistics and Epidemiology, Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina (United States); Richardson, Susan, E-mail: srichardson@radonc.wustl.edu [Department of Radiation Oncology, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri (United States)

2012-05-01

390

Low Dose Radiation Research  

NSDL National Science Digital Library

The US Department of Energy's Low Dose Radiation Research Program supports research that investigates the health risks from exposure to radiation at low levels. This Web site provides an overview of radiation biology, up-to-date information and archived results from program-related research, and other resources for the benefit of researchers and the general public alike. Some research projects include comparing low dose radiation to endogenous oxidative damage, determining thresholds for radiation exposure, determining genetics factors that make some individuals more susceptible to radiation-induced damage, and more.

391

Solar modulation of dose rate onboard the Mir station  

Microsoft Academic Search

Models of the radiation belts that are currently used to estimate exposure for astronauts describe the environment at times of either solar minimum or solar maximum. Static models, constructed using data acquired prior to 1970 during a solar cycle with relatively low solar radio flux, have flux uncertainties of a factor of two to five and dose-rate uncertainties of a

G. D. Badhwar; V. A. Shurshakov; V. V. Tstelin

1997-01-01

392

High dose uranium ion implantation into silicon  

SciTech Connect

Implantation of uranium ions into silicon to a maximum dose of 6 x 10/sup 16/ atoms/cm/sup 2/, with a maximum concentration of 6 x 10/sup 21/ atoms/cm/sup 3/, has been carried out. This concentration corresponds to 12 at. % of uranium in the silicon host material. The implanted uranium content was measured by Rutherford backscattering and confirmed by a measurement of the alpha-particle activity of the buried uranium layer. The range and straggling of the uranium, and sputtering of the silicon target by uranium, were measured and are compared with theoretical estimates. The implantation was performed at an ion mean energy of 157 keV using a new kind of high current metal ion source.

Brown, I.G.; Galvin, J.E.; Yu, K.M.

1987-05-01

393

Maximum acceptable weights and maximum voluntary isometric strengths for asymmetric lifting  

Microsoft Academic Search

A laboratory study was conducted to determine the effects of asymmetric lifting on psychophysically determined maximum acceptable weights and maximum voluntary isometric strengths. Thirteen male college students lifted three different boxes in the sagittal plane and at three different angles of asymmetry (30,60 and 90°) from floor to an 81-cm high table using a free-style lifting technique. For each lifting

A. GARG; DON BADGER

1986-01-01

394

On determining dose rate constants spectroscopically  

SciTech Connect

Purpose: To investigate several aspects of the Chen and Nath spectroscopic method of determining the dose rate constants of {sup 125}I and {sup 103}Pd seeds [Z. Chen and R. Nath, Phys. Med. Biol. 55, 6089-6104 (2010)] including the accuracy of using a line or dual-point source approximation as done in their method, and the accuracy of ignoring the effects of the scattered photons in the spectra. Additionally, the authors investigate the accuracy of the literature's many different spectra for bare, i.e., unencapsulated {sup 125}I and {sup 103}Pd sources. Methods: Spectra generated by 14 {sup 125}I and 6 {sup 103}Pd seeds were calculated in vacuo at 10 cm from the source in a 2.7 Multiplication-Sign 2.7 Multiplication-Sign 0.05 cm{sup 3} voxel using the EGSnrc BrachyDose Monte Carlo code. Calculated spectra used the initial photon spectra recommended by AAPM's TG-43U1 and NCRP (National Council of Radiation Protection and Measurements) Report 58 for the {sup 125}I seeds, or TG-43U1 and NNDC(2000) (National Nuclear Data Center, 2000) for {sup 103}Pd seeds. The emitted spectra were treated as coming from a line or dual-point source in a Monte Carlo simulation to calculate the dose rate constant. The TG-43U1 definition of the dose rate constant was used. These calculations were performed using the full spectrum including scattered photons or using only the main peaks in the spectrum as done experimentally. Statistical uncertainties on the air kerma/history and the dose rate/history were Less-Than-Or-Slanted-Equal-To 0.2%. The dose rate constants were also calculated using Monte Carlo simulations of the full seed model. Results: The ratio of the intensity of the 31 keV line relative to that of the main peak in {sup 125}I spectra is, on average, 6.8% higher when calculated with the NCRP Report 58 initial spectrum vs that calculated with TG-43U1 initial spectrum. The {sup 103}Pd spectra exhibit an average 6.2% decrease in the 22.9 keV line relative to the main peak when calculated with the TG-43U1 rather than the NNDC(2000) initial spectrum. The measured values from three different investigations are in much better agreement with the calculations using the NCRP Report 58 and NNDC(2000) initial spectra with average discrepancies of 0.9% and 1.7% for the {sup 125}I and {sup 103}Pd seeds, respectively. However, there are no differences in the calculated TG-43U1 brachytherapy parameters using either initial spectrum in both cases. Similarly, there were no differences outside the statistical uncertainties of 0.1% or 0.2%, in the average energy, air kerma/history, dose rate/history, and dose rate constant when calculated using either the full photon spectrum or the main-peaks-only spectrum. Conclusions: Our calculated dose rate constants based on using the calculated on-axis spectrum and a line or dual-point source model are in excellent agreement (0.5% on average) with the values of Chen and Nath, verifying the accuracy of their more approximate method of going from the spectrum to the dose rate constant. However, the dose rate constants based on full seed models differ by between +4.6% and -1.5% from those based on the line or dual-point source approximations. These results suggest that the main value of spectroscopic measurements is to verify full Monte Carlo models of the seeds by comparison to the calculated spectra.

Rodriguez, M.; Rogers, D. W. O. [Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa K1S 5B6 (Canada)

2013-01-15

395

Low-Dose Carcinogenicity Studies  

EPA Science Inventory

One of the major deficiencies of cancer risk assessments is the lack of low-dose carcinogenicity data. Most assessments require extrapolation from high to low doses, which is subject to various uncertainties. Only 4 low-dose carcinogenicity studies and 5 low-dose biomarker/pre-n...

396

Maximum aposteriori joint source/channel coding  

NASA Technical Reports Server (NTRS)

A maximum aposteriori probability (MAP) approach to joint source/channel coder design is presented in this paper. This method attempts to explore a technique for designing joint source/channel codes, rather than ways of distributing bits between source coders and channel coders. For a nonideal source coder, MAP arguments are used to design a decoder which takes advantage of redundancy in the source coder output to perform error correction. Once the decoder is obtained, it is analyzed with the purpose of obtaining 'desirable properties' of the channel input sequence for improving overall system performance. Finally, an encoder design which incorporates these properties is proposed.

Sayood, Khalid; Gibson, Jerry D.

1991-01-01

397

Maximum likelihood identification for large space structures  

NASA Technical Reports Server (NTRS)

This paper examines the use of on-orbit identification based on Maximum Likelihood Estimation (MLE) to provide these high-order, high-accuracy control design models for large space structures (LSS's). First, it outlines a general MLE identification algorithm, together with a covariance-analysis procedure to assess algorithm performance in terms of systematic and stochastic errors. Next, it examines various simplifications appropriate for the LSS identification application. Simplified analytical performance results are presented, as are numerical results to support these analyses. Finally, a graphical interpretation of these results is given.

Barrett, Michael F.; Enns, Dale F.

1988-01-01

398

Dynamical maximum entropy approach to flocking  

NASA Astrophysics Data System (ADS)

We derive a new method to infer from data the out-of-equilibrium alignment dynamics of collectively moving animal groups, by considering the maximum entropy model distribution consistent with temporal and spatial correlations of flight direction. When bird neighborhoods evolve rapidly, this dynamical inference correctly learns the parameters of the model, while a static one relying only on the spatial correlations fails. When neighbors change slowly and the detailed balance is satisfied, we recover the static procedure. We demonstrate the validity of the method on simulated data. The approach is applicable to other systems of active matter.

Cavagna, Andrea; Giardina, Irene; Ginelli, Francesco; Mora, Thierry; Piovani, Duccio; Tavarone, Raffaele; Walczak, Aleksandra M.

2014-04-01

399

Dynamical maximum entropy approach to flocking.  

PubMed

We derive a new method to infer from data the out-of-equilibrium alignment dynamics of collectively moving animal groups, by considering the maximum entropy model distribution consistent with temporal and spatial correlations of flight direction. When bird neighborhoods evolve rapidly, this dynamical inference correctly learns the parameters of the model, while a static one relying only on the spatial correlations fails. When neighbors change slowly and the detailed balance is satisfied, we recover the static procedure. We demonstrate the validity of the method on simulated data. The approach is applicable to other systems of active matter. PMID:24827278

Cavagna, Andrea; Giardina, Irene; Ginelli, Francesco; Mora, Thierry; Piovani, Duccio; Tavarone, Raffaele; Walczak, Aleksandra M

2014-04-01

400

Superstatistical distributions from a maximum entropy principle.  

PubMed

We deal with a generalized statistical description of nonequilibrium complex systems based on least biased distributions given some prior information. A maximum entropy principle is introduced that allows for the determination of the distribution of the fluctuating intensive parameter beta of a superstatistical system, given certain constraints on the complex system under consideration. We apply the theory to three examples: the superstatistical quantum-mechanical harmonic oscillator, the superstatistical classical ideal gas, and velocity time series as measured in a turbulent Taylor-Couette flow. PMID:19113089

Van der Straeten, Erik; Beck, Christian

2008-11-01

401

Conductivity maximum in a charged colloidal suspension  

SciTech Connect

Molecular dynamics simulations of a charged colloidal suspension in the salt-free regime show that the system exhibits an electrical conductivity maximum as a function of colloid charge. We attribute this behavior to two main competing effects: colloid effective charge saturation due to counterion 'condensation' and diffusion slowdown due to the relaxation effect. In agreement with previous observations, we also find that the effective transported charge is larger than the one determined by the Stern layer and suggest that it corresponds to the boundary fluid layer at the surface of the colloidal particles.

Bastea, S

2009-01-27

402

The Maximum Size of Dynamic Data Structures  

E-print Network

SIAM J. COMPUT.Vol. 20, No. 5, pp. 807-823, October 1991 1991 Society for Industrial and Applied Mathematics001 THE MAXIMUM SIZE OF DYNAMIC DATA STRUCTURES* CLAIRE M. KENYON-MATHIEU’ AND JEFFREY SCOTT VITTER$ Abstract. This paper develops two... Science Foundation grant andby a National Science Foundation Presidential Young Investigator Award with matching funds from IBM. 807 808 C. M. KENYON-MATHIEU AND J. S. VITTER Data structures process a sequence ofitems over time; at time the data structure...

Kenyon-Mathieu, Claire M.; Vitter, Jeffrey Scott

1991-10-01

403

The 2009 Perseid Maximum - Photographic Results  

NASA Astrophysics Data System (ADS)

An astronomical camp was organized by Comet and Meteors Workshop during the 2009 Perseids maximum. 69 meteors were photographed during four consecutive nights. We found that photographic Perseid radiant was very compact and located at alpha=48.7 deg, delta=58.6 deg. Our main goal was the determination of the radiant from single station photographic observations, however we also calculated two double station trajectories using additional data which were send to us by casual photographic observer from other parts of Poland. Dozens of radio reflections were observed with simple radio receiver, some of them were identified with photographic images.

Zolcadek, P.; Wisniewski, M.; Polakowski, K.; Wala, E.; Walczak, K.; Poleski, R.

2010-01-01

404

Maximum a posteriori decoder for digital communications  

NASA Technical Reports Server (NTRS)

A system and method for decoding by identification of the most likely phase coded signal corresponding to received data. The present invention has particular application to communication with signals that experience spurious random phase perturbations. The generalized estimator-correlator uses a maximum a posteriori (MAP) estimator to generate phase estimates for correlation with incoming data samples and for correlation with mean phases indicative of unique hypothesized signals. The result is a MAP likelihood statistic for each hypothesized transmission, wherein the highest value statistic identifies the transmitted signal.

Altes, Richard A. (Inventor)

1997-01-01

405

Statistical variability and confidence intervals for planar dose QA pass rates  

SciTech Connect

Purpose: The most common metric for comparing measured to calculated dose, such as for pretreatment quality assurance of intensity-modulated photon fields, is a pass rate (%) generated using percent difference (%Diff), distance-to-agreement (DTA), or some combination of the two (e.g., gamma evaluation). For many dosimeters, the grid of analyzed points corresponds to an array with a low areal density of point detectors. In these cases, the pass rates for any given comparison criteria are not absolute but exhibit statistical variability that is a function, in part, on the detector sampling geometry. In this work, the authors analyze the statistics of various methods commonly used to calculate pass rates and propose methods for establishing confidence intervals for pass rates obtained with low-density arrays. Methods: Dose planes were acquired for 25 prostate and 79 head and neck intensity-modulated fields via diode array and electronic portal imaging device (EPID), and matching calculated dose planes were created via a commercial treatment planning system. Pass rates for each dose plane pair (both centered to the beam central axis) were calculated with several common comparison methods: %Diff/DTA composite analysis and gamma evaluation, using absolute dose comparison with both local and global normalization. Specialized software was designed to selectively sample the measured EPID response (very high data density) down to discrete points to simulate low-density measurements. The software was used to realign the simulated detector grid at many simulated positions with respect to the beam central axis, thereby altering the low-density sampled grid. Simulations were repeated with 100 positional iterations using a 1 detector/cm{sup 2} uniform grid, a 2 detector/cm{sup 2} uniform grid, and similar random detector grids. For each simulation, %/DTA composite pass rates were calculated with various %Diff/DTA criteria and for both local and global %Diff normalization techniques. Results: For the prostate and head/neck cases studied, the pass rates obtained with gamma analysis of high density dose planes were 2%-5% higher than respective %/DTA composite analysis on average (ranging as high as 11%), depending on tolerances and normalization. Meanwhile, the pass rates obtained via local normalization were 2%-12% lower than with global maximum normalization on average (ranging as high as 27%), depending on tolerances and calculation method. Repositioning of simulated low-density sampled grids leads to a distribution of possible pass rates for each measured/calculated dose plane pair. These distributions can be predicted using a binomial distribution in order to establish confidence intervals that depend largely on the sampling density and the observed pass rate (i.e., the degree of difference between measured and calculated dose). These results can be extended to apply to 3D arrays of detectors, as well. Conclusions: Dose plane QA analysis can be greatly affected by choice of calculation metric and user-defined parameters, and so all pass rates should be reported with a complete description of calculation method. Pass rates for low-density arrays are subject to statistical uncertainty (vs. the high-density pass rate), but these sampling errors can be modeled using statistical confidence intervals derived from the sampled pass rate and detector density. Thus, pass rates for low-density array measurements should be accompanied by a confidence interval indicating the uncertainty of each pass rate.

Bailey, Daniel W.; Nelms, Benjamin E.; Attwood, Kristopher; Kumaraswamy, Lalith; Podgorsak, Matthew B. [Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260 (United States) and Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States); Canis Lupus LLC, Merrimac, Wisconsin 53561 (United States); Department of Biostatistics, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States); Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States); Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States); Department of Molecular and Cellular Biophysics and Biochemistry, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States) and Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214 (United States)

2011-11-15

406

A simple method of independent treatment time verification in gamma knife radiosurgery using integral dose  

Microsoft Academic Search

The purpose of this study is to develop a simple independent dose calculation method to verify treatment plans for Leksell Gamma Knife radiosurgery. Our approach uses the total integral dose within the skull as an end point for comparison. The total integral dose is computed using a spreadsheet and is compared to that obtained from Leksell GammaPlan registered . It

Jian-Yue Jin; Robert Drzymala; Li Zuofeng

2004-01-01

407

Low dose proteasome inhibition affects alternative splicing.  

PubMed

Protein degradation by the ubiquitin proteasome system ensures controlled degradation of structural proteins, signaling mediators, and transcription factors. Inhibition of proteasome function by specific proteasome inhibitors results in dose-dependent cellular effects ranging from induction of apoptosis to protective stress responses. The present study seeks to identify nuclear regulators mediating the protective stress response to low dose proteasome inhibition. Primary human endothelial cells were treated with low doses of the proteasome inhibitor MG132 for 2 h, and proteomic analysis of nuclear extracts was performed. Using a 2-D differential in gel electrophoresis (DIGE) approach, we identified more than 24 splice factors to be differentially regulated by low dose proteasome inhibition. In particular, several isoforms of hnRNPA1 were shown to be increased, pointing toward altered posttranslational modification of hnRNPA1 upon proteasome inhibition. Elevated levels of splice factors were associated with a different alternative splicing pattern in response to proteasome inhibition as determined by Affymetrix exon array profiling. Of note, we observed alternative RNA processing for stress associated genes such as caspases and heat shock proteins. Our study provides first evidence that low dose proteasome inhibition affects posttranscriptional regulation of splice factors and early alternative splicing events. PMID:22702956

Bieler, Sven; Hammer, Elke; Gesell-Salazar, Manuela; Völker, Uwe; Stangl, Karl; Meiners, Silke

2012-08-01

408

Prescribed dose versus calculated dose of spinal cord in standard head and neck irradiation assessed by 3-D plan  

PubMed Central

Background and Purpose: Spinal cord toxicity can be dreaded complication while treating head and neck cancer by conventional radiotherapy. Cord sparing approach is applied by two phase planning in conventional head neck radiotherapy. In spite of cord sparing approach spinal cord still receives considerable scatter dose. Our study aims to do the volumetric analysis of spinal cord dosimetry and to correlate with the clinical findings. Materials and Methods: Treatment planning was done in two phases. First phase treatment fields include gross disease- both tumor and involved nodes. in the second phase, treatment field shrinkage was done to cover the gross disease sparing the spinal cord. These fields are termed as off-cord fields. 42 patients with histological proven squamous cell carcinoma of the head and neck region were analysed with two groups. In Group A, 46 Gy was given in 23 fractions, and then tumor-boost with off-cord field received 24 Gy in 12 fractions. In Group B 50 Gy was prescribed in 25 fractions initially, then off-cord field given 20 Gy in 10 fractions to analyze theoutcome. Planning Computed tomography (CT) scan was done Philips Brilliance 16 slice CT scan machine, and contouring and dose calculation were done at ASHA treatment planning software. Results: Maximum dose and dose at 1 cm3, 2 cm3, and 5 cm3 were calculated. Maximum dose to cord was 52.6 Gy (range 48.1-49.7 Gy) in Group A and 54.3 Gy (range 51.48-52.33 Gy) in Group B initially. Off-cord fields received mean dose 8.07 Gy (85.85% of maximum) in Group A and 5.47 Gy (86.84% of maximum) in Group B. At the end of 6 months from the last date of radiotherapy, grade 1 spinal cord toxicity found in two patients in Group A and one patient in Group B respectively (P = 0.55). Both groups received additional dose, which are higher than the prescribed dose, but no patients show significant spinal cord toxicity after 6 month of follow-up. Conclusion: Spinal cord received scatter dose which much higher than the predicted dose in conventional radiotherapy of head neck cancer. Short term follow up failed to establish clinical correlation with volumetric dose of spinal cord. Two phase cord sparing head neck radiation planning if practiced should be used with caution. PMID:24665442

Majumder, Dipanjan; Patra, Niladri Bihari; Chatterjee, Debashis; Mallick, Swapan Kumar; Kabasi, Apurba Kumar; Majumder, Anjali

2014-01-01

409

External Dose Estimates from  

E-print Network

residents of counties in the eastern and Midwestern U.S. that received above average rainfall were impacted to the Population of the Continental U.S. from High Yield Weapons Tests Conducted by the U.S., U.K. and U.S exposure and whole body effective dose received by residents of the continental U.S. during the period 1953

410

Utirik Atoll Dose Assessment  

Microsoft Academic Search

On March 1, 1954, radioactive fallout from the nuclear test at Bikini Atoll code-named BRAVO was deposited on Utirik Atoll which lies about 187 km (300 miles) east of Bikini Atoll. The residents of Utirik were evacuated three days after the fallout started and returned to their atoll in May 1954. In this report we provide a final dose assessment

William L. Robison; Cynthia L. Conrado; Kenneth T. Bogen

1999-01-01

411

Calculation of the uncertainty in the dose delivered during radiation therapy  

SciTech Connect

There is, inevitably, uncertainty in our knowledge of the dose at any point within an irradiated patient. A technique is presented for estimating this uncertainty by performing three parallel calculations, one using nominal values and the others extreme values of the parameters upon which the dose depends. Such calculations can be made with almost any algorithm for calculating dose. They result in an estimate, at some specified confidence level which is determined by the data used, of the range of dose likely at any point. Such calculations should help therapists to avert over- or underdosage which might not be evident in conventional calculations of the nominal dose.

Goitein, M.

1985-09-01

412

Mars surface radiation exposure for solar maximum conditions and 1989 solar proton events  

NASA Technical Reports Server (NTRS)

The Langley heavy-ion/nucleon transport code, HZETRN, and the high-energy nucleon transport code, BRYNTRN, are used to predict the propagation of galactic cosmic rays (GCR's) and solar flare protons through the carbon dioxide atmosphere of Mars. Particle fluences and the resulting doses are estimated on the surface of Mars for GCR's during solar maximum conditions and the Aug., Sep., and Oct. 1989 solar proton events. These results extend previously calculated surface estimates for GCR's at solar minimum conditions and the Feb. 1956, Nov. 1960, and Aug. 1972 solar proton events. Surface doses are estimated with both a low-density and a high-density carbon dioxide model of the atmosphere for altitudes of 0, 4, 8, and 12 km above the surface. A solar modulation function is incorporated to estimate the GCR dose variation between solar minimum and maximum conditions over the 11-year solar cycle. By using current Mars mission scenarios, doses to the skin, eye, and blood-forming organs are predicted for short- and long-duration stay times on the Martian surface throughout the solar cycle.

Simonsen, Lisa C.; Nealy, John E.

1992-01-01

413

Turning point Getting started  

E-print Network

Point is compatible with Powerpoint and to access TurningPoints functions simple open any powerpoint file through simply create a powerpoint presentation and then open it in TurningPoint and insert the questions you wish to have. When the program is open, the interface will look like powerpoint, with an additional tab

Uppsala Universitet

414

CRYSTALLOGRAPHIC POINT AND SPACE  

E-print Network

CRYSTALLOGRAPHIC POINT AND SPACE GROUPS Andy Elvin June 10, 2013 #12;Contents Point and Space no reflection axes #12;Cube and Octahedron are dual Symmetries under Oh #12;Space Groups Subgroups of E(3) Point Group + Translation { R | 0 }{ E | t }a = { R | t }a = Ra + t 230 Space Groups 73 symmorphic space

California at Santa Cruz, University of

415

Maximum Diameter of Impacting Liquid Droplets  

NASA Astrophysics Data System (ADS)

The maximum diameter a droplet that impacts on a surface will attain is the subject of controversy, notably for high-velocity impacts of low-viscosity liquids such as water or blood. We study the impact of droplets of simple liquids of different viscosities, and a shear-thinning complex fluid (blood), for a wide range of surfaces, impact speeds, and impact angles. We show that the spreading behavior cannot simply be predicted by equating the inertial to either capillary or viscous forces, since, for most situations of practical interest, all three forces are important. We determine the correct scaling behaviors for the viscous and capillary regimes and, by interpolating between the two, allow for a universal rescaling. The results for different impact angles can be rescaled on this universal curve also, by doing a simple geometrical correction for the impact angle. For blood, we show that the shear-thinning properties do not affect the maximum diameter and only the high-shear rate viscosity is relevant. With our study, we solve a long-standing problem within the fluid-dynamics community: We attest that the spreading behavior of droplets is governed by the conversion of kinetic energy into surface energy or dissipated heat. Energy transfer into internal flows marginally hinders droplet spreading upon impact.

Laan, Nick; de Bruin, Karla G.; Bartolo, Denis; Josserand, Christophe; Bonn, Daniel

2014-10-01

416

Data required for testicular dose calculation during radiotherapy of seminoma  

SciTech Connect

The purpose of this study was to provide the required data for the direct calculation of testicular dose resulting from radiotherapy in patients with seminoma. Paraortic (PA) treatment fields and dog-leg (DL) portals including paraortic and ipsilateral pelvic nodes were simulated on a male anthropomorphic phantom equipped with an artificial testicle. Anterior and posterior irradiations were performed for five different PA and DL field dimensions. Dose measurements were carried out using a calibrated ionization chamber. The dependence of testicular dose upon the distance separating the testicle from the treatment volume and upon the tissue thickness at the entrance point of the beam was investigated. A clamshell lead shield was used to reduce testicular dose. The scattered dose to testicle was measured in nine patients using thermoluminescent dosimeters. Phantom and patient exposures were generated with a 6 MV x-ray beam. Linear and nonlinear regression analysis was employed to obtain formulas describing the relation between the radiation dose to an unshielded and/or shielded testicle with the field size and the distance from the inferior field edge. Correction factors showing the variation of testicular dose with the patient thickness along beam axis were found. Bland-Altman statistical analysis showed that testicular dose obtained by the proposed calculation method may differ from the measured dose value by less than 25%. The current study presents a method providing reasonable estimations of testicular dose for individual patients undergoing PA or DL radiotherapy.

Mazonakis, Michalis; Kokona, Georgiana; Varveris, Haralambos; Damilakis, John; Gourtsoyiannis, Nicholas [Department of Medical Physics, University Hospital of Iraklion, 71110 Iraklion (Greece); Department of Radiotherapy, Faculty of Medicine, University of Crete, 71409 Iraklion (Greece); Department of Medical Physics, Faculty of Medicine, University of Crete, 71409 Iraklion (Greece); Department of Radiology, Faculty of Medicine, University of Crete, 71409 Iraklion (Greece)

2006-07-15

417

Relative dose distribution in gamma knife treatment near tissue inhomogeneties.  

PubMed

The primary goal in this study was to investigate 3-D dose distribution, near the areas of tissue inhomogeneities, in Gamma Knife Radiosurgery with the gel dosimetry. The spherical glass balloon of a diameter of 16 cm filled with the gel forms the homogeneous phantom; and an identical balloon with two corks placed on each side to represent the air cavities forms the inhomogeneous phantom. Dose calibration is performed by irradiating vials at known doses and then utilizing the R2- dose calibration curve. Stereotactic frames and fudicial markers were attached to the phantoms for MR scanning and image processing. Dose distributions from a single shot, using all 201 Cobalt sources, delivered to a known point with identical coordinates, are calculated both in homogeneous and inhomogeneous gel phantoms. In the aspect of dosimetrical quality control, the Gamma Knife planning system predicted dose distribution is compared with the experimental results. In the homogeneous phantom, the gel dosimetry calculated dose distribution is in good agreement with the GammaPlan predicted dose distribution. However, with the inhomogeneous phantom, the dose distribution is spatially different and significant differences in dose levels are observed. PMID:17282896

Isbakan, Fatih; Buyuksarac, Bora; Agus, Onur; Ulgen, Yekta; Bilge, Hatice; Ozen, Zeynep

2005-01-01

418

Patient-specific dose calculation methods for high-dose-rate iridium-192 brachytherapy  

NASA Astrophysics Data System (ADS)

In high-dose-rate 192Ir brachytherapy, the radiation dose received by the patient is calculated according to the AAPM Task Group 43 (TG-43) formalism. This table-based dose superposition method uses dosimetry parameters derived with the radioactive 192Ir source centered in a water phantom. It neglects the dose perturbations caused by inhomogeneities, such as the patient anatomy, applicators, shielding, and radiographic contrast solution. In this work, we evaluated the dosimetric characteristics of a shielded rectal applicator with an endocavitary balloon injected with contrast solution. The dose distributions around this applicator were calculated by the GEANT4 Monte Carlo (MC) code and measured by ionization chamber and GAFCHROMIC EBT film. A patient-specific dose calculation study was then carried out for 40 rectal treatment plans. The PTRAN_CT MC code was used to calculate the dose based on computed tomography (CT) images. This study involved the development of BrachyGUI, an integrated treatment planning tool that can process DICOM-RT data and create PTRAN_CT input initialization files. BrachyGUI also comes with dose calculation and evaluation capabilities. We proposed a novel scatter correction method to account for the reduction in backscatter radiation near tissue-air interfaces. The first step requires calculating the doses contributed by primary and scattered photons separately, assuming a full scatter environment. The scatter dose in the patient is subsequently adjusted using a factor derived by MC calculations, which depends on the distances between the point of interest, the 192Ir source, and the body contour. The method was validated for multicatheter breast brachytherapy, in which the target and skin doses for 18 patient plans agreed with PTRAN_CT calculations better than 1%. Finally, we developed a CT-based analytical dose calculation method. It corrects for the photon attenuation and scatter based upon the radiological paths determined by ray tracing. The scatter dose is again adjusted using our scatter correction technique. The algorithm was tested using phantoms and actual patient plans for head-and-neck, esophagus, and MammoSite breast brachytherapy. Although the method fails to correct for the changes in lateral scatter introduced by inhomogeneities, it is a major improvement over TG-43 and is sufficiently fast for clinical use.

Poon, Emily S.

419

Point-to-Point Multicast Communications Protocol  

NASA Technical Reports Server (NTRS)

This paper describes a protocol to support point-to-point interprocessor communications with multicast. Dynamic, cut-through routing with local flow control is used to provide a high-throughput, low-latency communications path between processors. In addition multicast transmissions are available, in which copies of a packet are sent to multiple destinations using common resources as much as possible. Special packet terminators and selective buffering are introduced to avoid a deadlock during multicasts. A simulated implementation of the protocol is also described.

Byrd, Gregory T.; Nakano, Russell; Delagi, Bruce A.

1987-01-01

420

Driving Performances of Solar Energy Powered Vehicle with Novel Maximum Power Tracking Control for a Solar Car Rally  

Microsoft Academic Search

This paper describes driving performance of solar energy powered vehicle for a solar car rally. The first topic is to present one of the maximum power point tracking (MPPT) control for the vehicle which have been proposed by authors. This novel control based vehicle is estimated from the view point of energy consumption, optimal speed and the total running distance

Y. Suita; S. Tadakuma

2006-01-01

421

[Radiation doses from patients undergoing yttrium-90 silicate knee radiosynovectomy].  

PubMed

The present study was undertaken because we could not find references related to the minimal radiation doses emitted from patients treated with (90)Y-silicate colloid ((90)Y-SC) for radiosynectomy (RS). Radiation doses from 16 patients treated with about 181+/-13 MBq (90)Y-SC for RS of knee synovitis were estimated by dose rate measurements performed within 10 min after the (90)Y-SC injection with a calibrated survey dose ratemeter at 0.5 m, 1 m and 2 m distances from the treated joint. The mean dose rate values from the patients after bg subtraction were 0.6+/-0.4 microSv/h at 0.5 m, 0.1+/-0.1 microSv/h at 1 m and 0.1 +/- 0.0 microSv/h at 2 m distance. Dose rates at a distance of 0.5 m were significantly correlated (P<0.02) with the patient's weight but not with the height or the injected activity. The assumed estimated maximum whole body doses from a treated patient were 55 microSv for persons living with the patient, 2.9-3.4 microSv for the nursing staff, 0.2-1.8 microSv for the therapist physician and 0.3-0.6 microSv for the technologist, involved in the whole procedure. The above values were lower than those published with the same methodology for alternative RS radiopharmaceuticals for knee synovitis like dysprosium-165 ferric hydroxide macroaggregate ((165)Dy-FHMA) or holmium-166 ((166)Ho-FHMA), as estimated with their typical injected activities. In conclusion our results demonstrate that in (90)Y-SC knee synovectomy, the whole body radiation doses to medical and non medical personnel were as expected well below the maximum annual dose limits for the public and professionals exposed to radiation. PMID:16617401

Badiavas, Kosmas; Chatzopoulos, Dimitrios; Markou, Pavlos

2006-01-01

422

Detection of ECG characteristic points using wavelet transforms  

Microsoft Academic Search

An algorithm based on wavelet transforms (WT's) has been developed for detecting ECG characteristic points. With the multiscale feature of WT's, the QRS complex can be distinguished from high P or T waves, noise, baseline drift, and artifacts. The relation between the characteristic points of ECG signal and those of modulus maximum pairs of its WT's is illustrated. By using

Cuiwei Li; Chongxun Zheng; Changfeng Tai

1995-01-01

423

Site-specific parameter values for the Nuclear Regulatory Commission's food pathway dose model  

Microsoft Academic Search

Routine operations at the Savannah River Site (SRS) in Western South Carolina result in radionuclide releases to the atmosphere and to the Savannah River. The resulting radiation doses to the off-site maximum individual and the off-site population within 80 km of the SRS are estimated on a yearly basis. These estimates are currently generated using dose models prescribed for the

D. M. Hamby

1992-01-01

424

Estimation of the Dose and Dose Rate Effectiveness Factor  

NASA Technical Reports Server (NTRS)

Current models to estimate radiation risk use the Life Span Study (LSS) cohort that received high doses and high dose rates of radiation. Transferring risks from these high dose rates to the low doses and dose rates received by astronauts in space is a source of uncertainty in our risk calculations. The solid cancer models recommended by BEIR VII [1], UNSCEAR [2], and Preston et al [3] is fitted adequately by a linear dose response model, which implies that low doses and dose rates would be estimated the same as high doses and dose rates. However animal and cell experiments imply there should be curvature in the dose response curve for tumor induction. Furthermore animal experiments that directly compare acute to chronic exposures show lower increases in tumor induction than acute exposures. A dose and dose rate effectiveness factor (DDREF) has been estimated and applied to transfer risks from the high doses and dose rates of the LSS cohort to low doses and dose rates such as from missions in space. The BEIR VII committee [1] combined DDREF estimates using the LSS cohort and animal experiments using Bayesian methods for their recommendation for a DDREF value of 1.5 with uncertainty. We reexamined the animal data considered by BEIR VII and included more animal data and human chromosome aberration data to improve the estimate for DDREF. Several experiments chosen by BEIR VII were deemed inappropriate for application to human risk models of solid cancer risk. Animal tumor experiments performed by Ullrich et al [4], Alpen et al [5], and Grahn et al [6] were analyzed to estimate the DDREF. Human chromosome aberration experiments performed on a sample of astronauts within NASA were also available to estimate the DDREF. The LSS cohort results reported by BEIR VII were combined with the new radiobiology results using Bayesian methods.

Chappell, L.; Cucinotta, F. A.

2013-01-01

425

Maximum Information and Quantum Prediction Algorithms  

E-print Network

This paper describes an algorithm for selecting a consistent set within the consistent histories approach to quantum mechanics and investigates its properties. The algorithm uses a maximum information principle to select from among the consistent sets formed by projections defined by the Schmidt decomposition. The algorithm unconditionally predicts the possible events in closed quantum systems and ascribes probabilities to these events. A simple spin model is described and a complete classification of all exactly consistent sets of histories formed from Schmidt projections in the model is proved. This result is used to show that for this example the algorithm selects a physically realistic set. Other tentative suggestions in the literature for set selection algorithms using ideas from information theory are discussed.

Jim McElwaine

1996-11-28

426

Approximate maximum likelihood decoding of block codes  

NASA Technical Reports Server (NTRS)

Approximate maximum likelihood decoding algorithms, based upon selecting a small set of candidate code words with the aid of the estimated probability of error of each received symbol, can give performance close to optimum with a reasonable amount of computation. By combining the best features of various algorithms and taking care to perform each step as efficiently as possible, a decoding scheme was developed which can decode codes which have better performance than those presently in use and yet not require an unreasonable amount of computation. The discussion of the details and tradeoffs of presently known efficient optimum and near optimum decoding algorithms leads, naturally, to the one which embodies the best features of all of them.

Greenberger, H. J.

1979-01-01

427

CLASSY: An adaptive maximum likelihood clustering algorithm  

NASA Technical Reports Server (NTRS)

The CLASSY clustering method alternates maximum likelihood iterative techniques for estimating the parameters of a mixture distribution with an adaptive procedure for splitting, combining, and eliminating the resultant components of the mixture. The adaptive procedure is based on maximizing the fit of a mixture of multivariate normal distributions to the observed data using its first through fourth central moments. It generates estimates of the number of multivariate normal components in the mixture as well as the proportion, mean vector, and covariance matrix for each component. The basic mathematical model for CLASSY and the actual operation of the algorithm as currently implemented are described. Results of applying CLASSY to real and simulated LANDSAT data are presented and compared with those generated by the iterative self-organizing clustering system algorithm on the same data sets.

Lennington, R. K.; Rassbach, M. E. (principal investigators)

1979-01-01

428

Maximum entropy model for business cycle synchronization  

NASA Astrophysics Data System (ADS)

The global economy is a complex dynamical system, whose cyclical fluctuations can mainly be characterized by simultaneous recessions or expansions of major economies. Thus, the researches on the synchronization phenomenon are key to understanding and controlling the dynamics of the global economy. Based on a pairwise maximum entropy model, we analyze the business cycle synchronization of the G7 economic system. We obtain a pairwise-interaction network, which exhibits certain clustering structure and accounts for 45% of the entire structure of the interactions within the G7 system. We also find that the pairwise interactions become increasingly inadequate in capturing the synchronization as the size of economic system grows. Thus, higher-order interactions must be taken into account when investigating behaviors of large economic systems.

Xi, Ning; Muneepeerakul, Rachata; Azaele, Sandro; Wang, Yougui

2014-11-01

429

On the Maximum Separation of Visual Binaries  

NASA Astrophysics Data System (ADS)

In this paper, an efficient algorithm is established for computing the maximum (minimum) angular separation ? max( ? min), the corresponding apparent position angles (?|_{?_max}, ?|_{?_min}) and the individual masses of visual binary systems. The algorithm uses Reed's formulae (1984) for the masses, and a technique of one-dimensional unconstrained minimization, together with the solution of Kepler's equation for (?_max, ?|_{?_max}) and (?_min, ?|_{?_min}). Iterative schemes of quadratic coverage up to any positive integer order are developed for the solution of Kepler's equation. A sample of 110 systems is selected from the Sixth Catalog of Orbits (Hartkopf et al. 2001). Numerical studies are included and some important results are as follows: (1) there is no dependence between ? max and the spectral type and (2) a minor modification of Giannuzzi's (1989) formula for the upper limits of ? max functions of spectral type of the primary.

Nouh, M. I.; Sharaf, M. A.

2012-12-01

430

Diffusivity Maximum in a Reentrant Nematic Phase  

PubMed Central

We report molecular dynamics simulations of confined liquid crystals using the Gay–Berne–Kihara model. Upon isobaric cooling, the standard sequence of isotropic–nematic–smectic A phase transitions is found. Upon further cooling a reentrant nematic phase occurs. We investigate the temperature dependence of the self-diffusion coefficient of the fluid in the nematic, smectic and reentrant nematic phases. We find a maximum in diffusivity upon isobaric cooling. Diffusion increases dramatically in the reentrant phase due to the high orientational molecular order. As the temperature is lowered, the diffusion coefficient follows an Arrhenius behavior. The activation energy of the reentrant phase is found in reasonable agreement with the reported experimental data. We discuss how repulsive interactions may be the underlying mechanism that could explain the occurrence of reentrant nematic behavior for polar and non-polar molecules. PMID:22837730

Stieger, Tillmann; Mazza, Marco G.; Schoen, Martin

2012-01-01

431

The worst case complexity of maximum parsimony.  

PubMed

Abstract One of the core classical problems in computational biology is that of constructing the most parsimonious phylogenetic tree interpreting an input set of sequences from the genomes of evolutionarily related organisms. We reexamine the classical maximum parsimony (MP) optimization problem for the general (asymmetric) scoring matrix case, where rooted phylogenies are implied, and analyze the worst case bounds of three approaches to MP: The approach of Cavalli-Sforza and Edwards, the approach of Hendy and Penny, and a new agglomerative, "bottom-up" approach we present in this article. We show that the second and third approaches are faster than the first one by a factor of [Formula: see text] and ?(n), respectively, where n is the number of species. PMID:25302568

Carmel, Amir; Musa-Lempel, Noa; Tsur, Dekel; Ziv-Ukelson, Michal

2014-11-01

432

On Using Unsatisfiability for Solving Maximum Satisfiability  

E-print Network

Maximum Satisfiability (MaxSAT) is a well-known optimization pro- blem, with several practical applications. The most widely known MAXS AT algorithms are ineffective at solving hard problems instances from practical application domains. Recent work proposed using efficient Boolean Satisfiability (SAT) solvers for solving the MaxSAT problem, based on identifying and eliminating unsatisfiable subformulas. However, these algorithms do not scale in practice. This paper analyzes existing MaxSAT algorithms based on unsatisfiable subformula identification. Moreover, the paper proposes a number of key optimizations to these MaxSAT algorithms and a new alternative algorithm. The proposed optimizations and the new algorithm provide significant performance improvements on MaxSAT instances from practical applications. Moreover, the efficiency of the new generation of unsatisfiability-based MaxSAT solvers becomes effectively indexed to the ability of modern SAT solvers to proving unsatisfiability and identifying unsatisfi...

Marques-Silva, Joao

2007-01-01

433

Distributed Maximum Likelihood Sensor Network Localization  

NASA Astrophysics Data System (ADS)

We propose a class of convex relaxations to solve the sensor network localization problem, based on a maximum likelihood (ML) formulation. This class, as well as the tightness of the relaxations, depends on the noise probability density function (PDF) of the collected measurements. We derive a computational efficient edge-based version of this ML convex relaxation class and we design a distributed algorithm that enables the sensor nodes to solve these edge-based convex programs locally by communicating only with their close neighbors. This algorithm relies on the alternating direction method of multipliers (ADMM), it converges to the centralized solution, it can run asynchronously, and it is computation error-resilient. Finally, we compare our proposed distributed scheme with other available methods, both analytically and numerically, and we argue the added value of ADMM, especially for large-scale networks.

Simonetto, Andrea; Leus, Geert

2014-03-01

434

The Emerging Low-Dose Therapy for Advanced Cancers  

PubMed Central

Generally minute doses of drugs have been prescribed in biotherapies, homeopathy, immunization and vaccinations for centuries. Now the use of low doses of drugs is on the rise to combat serious diseases such as advanced cancers around the world. This new therapeutic approach to address solid tumors and other advanced diseases is a departure from the conventional use of maximum dose protocol. A small dose of the prescribed drug is frequently administered in a continuous fashion, at regular intervals, either as a standard treatment or as a maintenance therapy for a long time. However, this new treatment method lacks any standard for drug quantization, dose fractionation, repetition frequency and duration of a treatment course for an individual patient. This paper reviews literature about metronomic therapy and discusses hormesis: both phenomena occur in low dose ranges. Better mathematical models, computer simulations, process optimization and clinical trials are warranted to fully exploit the potential of low dose metronomic therapy to cure chronic and complicated diseases. New protocols to standardize metronomic dosimetry will answer the age old questions related to hormesis and homeopathy. It appears that this new low-dose metronomic therapy will have far reaching effects in curing chronic diseases throughout the world. PMID:19809540

Satti, Jahangir

2009-01-01