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ABSTRACT: A method for the determination of 10 wood preservatives of chlorophenols (2,4-dichlorophenol, 2, 4, 6-trichlorophenol, 2, 4, 5-trichlorophenol, 2, 3, 4, 6-tetrachlorophenol, pentachlorophenol, lindane) and pyrethroids (permethrin, cyfluthrin, cypermethrin, delta-methrin) in furniture by solid phase extraction (SPE) coupled with gas chromatography-mass spectrometry (GC-MS) was developed. The furniture samples were extracted twice by ultrasonic extraction in methanol. The extract was then evaporated and acetylated by the acetic anhydride and potassium carbonate. Finally the reaction solution was purified by Oasis HLB SPE column. The wood preservatives were eluted by ethyl acetate and collected for analysis by GC-MS. The ten wood preservatives can be separated and determined successfully by this method. Under the optimized conditions, the detection limits of the six chlorophenol compounds were 1 mg/kg, and the four pyrethroid compounds were 5 mg/kg, and the spiked recoveries of the 10 wood preservatives in samples were in the range of 76.0% - 108.8%. Forty commercial wooden furniture samples were tested and lindane was found in some samples. The results showed that the method is accurate, rapid and sensitive. It can be effectively used to analyze the wood preservatives in wooden furniture.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 06/2012; 30(6):596-601.
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ABSTRACT: An analytical method for the simultaneous determination of 6 antibiotics (minocycline, oxytetracycline, tetracycline hydrochloride, chlorotetracycline hydrochloride, doxycycline hydrochloride and chloramphenicol) and metronidazole in acne removal products of cosmetic was established using high performance liquid chromatography (HPLC). The drugs in the sample were extracted with methanol. The separation was performed on an Agilent ZORBAX SB-C18 column (250 mm x 4.6 mm, 5 microm) at 20 degrees C with methanol, acetonitrile and 0.002 mol/L oxalic acid solution as mobile phases with gradient elution at a flow rate of 0.8 mL/min. The detection was performed by a diode array detector (DAD) at 268 nm. The injection volume was 10 microL. The quantification was performed by external standard method. The calibration curves showed good linearity within the range of 1 - 30 mg/L with the correlation coefficients no less than 0.997 0. The detection limits were in the range of 1.1 - 1.2 microg/g. The recoveries were between 91.9% and 107.7% in three spiked levels of 5, 10 and 20 mg/L with the relative standard deviations (RSDs) of 0.13% - 1.74%. The method was used in the analysis of acne removal products, and metronidazole was found in 15% of the total test samples. The method is rapid, sensitive, accurate, effective in separation, and can be used in the determination of the six antibiotics and metronidazole in acne removal products.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 06/2012; 30(6):641-6.
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ABSTRACT: In this paper, we study the problems of (approximately) representing a functional curve in 2-D by a set of curves with fewer
peaks. Representing a function (or its curve) by certain classes of structurally simpler functions (or their curves) is a
basic mathematical problem. Problems of this kind also find applications in applied areas such as intensity-modulated radiation
therapy (IMRT). Let f\bf f be an input piecewise linear functional curve of size n. We consider several variations of the problems. (1) Uphill–downhill pair representation (UDPR): Find two nonnegative piecewise
linear curves, one nondecreasing (uphill) and one nonincreasing (downhill), such that their sum exactly or approximately represents
f\bf f. (2) Unimodal representation (UR): Find a set of unimodal (single-peak) curves such that their sum exactly or approximately
represents f\bf f. (3) Fewer-peak representation (FPR): Find a piecewise linear curve with at most k peaks that exactly or approximately represents f\bf f. Furthermore, for each problem, we consider two versions. For the UDPR problem, we study its feasibility version: Given ε>0, determine whether there is a feasible UDPR solution for f\bf f with an approximation error ε; its min-ε version: Compute the minimum approximation error ε
∗ such that there is a feasible UDPR solution for f\bf f with errorε
∗. For the UR problem, we study its min-k version: Given ε>0, find a feasible solution with the minimum number k
∗ of unimodal curves for f\bf f with an error ε; its min-ε version: given k>0, compute the minimum error ε
∗ such that there is a feasible solution with at most k unimodal curves for f\bf f with error ε
∗. For the FPR problem, we study its min-k version: Given ε>0, find one feasible curve with the minimum number k
∗ of peaks for f\bf f with an error ε; its min-ε version: given k≥0, compute the minimum error ε
∗ such that there is a feasible curve with at most k peaks for f\bf f with error ε
∗. Little work has been done previously on solving these functional curve representation problems. We solve all the problems
(except the UR min-ε version) in optimal O(n) time, and the UR min-ε version in O(n+mlog m) time, where m<n is the number of peaks of f\bf f. Our algorithms are based on new geometric observations and interesting techniques.
KeywordsCurve approximation–Curve simplification–Curves with fewer peaks–Algorithm design
Discrete and Computational Geometry 04/2012; 46(2):334-360. · 0.94 Impact Factor
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ABSTRACT: In this paper, we consider an optimization problem in discrete geometry, called coupled path planning (CPP). Given a finite rectangular grid and a non-negative functionf defined on the horizontal axis of the grid, we seek two non-crossing monotone paths in the grid, such that the vertical difference
between the two paths approximatesf in the best possible way. This problem arises in intensity-modulated radiation therapy (IMRT), wheref represents an ideal radiation dose distribution and the two coupled paths represent the motion trajectories (or control sequence)
of two opposing metal leaves of a delivery device for controlling the area exposed to the radiation source. By finding an
optimal control sequence, the CPP problem aims to deliver precisely a prescribed radiation dose, while minimizing the side-effects
on the surrounding normal tissue. We present efficient algorithms for different versions of the CPP problems. Our results
are based on several new ideas and geometric observations, and substantially improve the solutions based on standard techniques.
Implementation results show that our CPP algorithms run fast and produce better quality clinical treatment plans than the
previous methods.
KeywordsIntensity-modulated radiation therapy (IMRT)–Intensity-modulated arc therapy (IMAT)–Single-arc IMRT–Arc-modulated radiation therapy (AMRT)–Coupled-path planning–Dynamic leaf sequencing
Algorithmica 04/2012; 60(1):152-174. · 0.60 Impact Factor
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ABSTRACT: Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt3M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2–3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt3M nanocatalysts validated the volcano curve established on extended surfaces, with Pt3Co being the most active alloy.Keywords: homogeneous alloy nanoparticles; Pt-bimetallic catalysts; oxygen reduction reaction; fuel cells; scanning electron microscopy
09/2011;
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Algorithmica. 01/2011; 61:656-673.
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ABSTRACT: In this paper, we present a theoretical study of several shape approximation problems, called shape rectangularization (SR), which arise in intensity-modulated radiation therapy (IMRT). Given a piecewise linear function f such that f(x)≥0 for any x∈ℝ, the SR problems seek an optimal set of constant window functions to approximate f under a certain error criterion, such that the sum of the resulting constant window functions equals (or well approximates)f. Aconstant window function W(⋅) is defined on an interval I such that W(x) is a fixed value h>0 for any x∈I and is 0 otherwise. Aconstant window function can be viewed as a rectangle (or ablock) geometrically, or as a vector with the consecutive a’s property combinatorially. The SR problems find applications in setup time and beam-on time minimization and dose simplification
of the IMRT treatment planning process. We show that the SR problems are APX-Hard, and thus we aim to develop theoretically
efficient and provably good quality approximation SR algorithms. Our main contribution is to present algorithms for a key
SR problem that achieve approximation ratios better than2. For the general case, we give a
\frac2413\frac{24}{13}-approximation algorithm. For unimodal input curves, we give a
\frac97\frac{9}{7}-approximation algorithm. We also consider other variants for which better approximation ratios are possible. We show that
an important SR case that has been studied in medical literature can be formulated as a k-MST(k-minimum-spanning-tree) problem on a certain geometric graph G; based on a set of geometric observations and a non-trivial dynamic programming scheme, we are able to compute an optimal
k-MST in G efficiently.
KeywordsShape rectangularization–Shape approximation–Integer linear programming–Dynamic programming–Intensity-modulated radiation therapy
Algorithmica 01/2011; 60:421-450. · 0.60 Impact Factor
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ABSTRACT: Four different biomass raw materials (corn stalk, reed, tobacco stalk, and banana leaves) were chosen to be deoxy-liquefied in an airtight vessel reactor for high-caloric fuel (HCF) production. The influence of temperature (573−723 K) on the product yields and chemical compositions of HCF from the four samples via deoxy-liquefaction were investigated. It was significant to find that the maximum content of alkanes was obtained at 673 K for corn stalk (35.98 mol %) and tobacco stalk (7.43 mol %), and 623 K for reed (32.56 mol %) and banana leaves (67.79 mol %), which was consistent with the optimum temperature for the highest yield of every sample. HCF from tobacco stalk (HCFt) was rich in phenolics and poor in hydrocarbons, whereas HCF from banana leaves (HCFb) was rich in hydrocarbon (alkanes: C7−C29; benzene derivatives) and poor in phenolics. The HCF from corn stalk and reed (HCFc and HCFr, respectively) were moderate. The composition of HCF had a great relationship with the holocellulose, lignin, and extractives content in the raw materials. Gas chromatography/mass spectrometry (GC/MS) and gas chromatography with a TCD detector (GC122) were used to determine the composition in HCF and in gaseous products, respectively.
11/2010;
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ABSTRACT: We study the problems of (approximately) representing a functional curve in 2-D by a set of curves with fewer peaks. Let f be an input nonnegative piecewise linear functional curve of size n. We consider the following problems. (1) Uphill-downhill pair representation (UDPR): Find two nonnegative piecewise linear
curves, one nondecreasing and one nonincreasing, such that their sum approximately represents f. (2) Unimodal representation (UR): Find a set of k nonnegative unimodal (single-peak) curves such that their sum approximately represents f. (3) Fewer-peak representation (FPR): Find a nonnegative piecewise linear curve with at most k peaks that approximately represents f. For each problem, we consider two versions. For UDPR, we study the feasibility version and the min-ε version. For each of the UR and FPR problems, we study the min-k version and the min-ε version. Little work has been done previously on these problems. We solve all problems (except the UR min-ε) in optimal O(n) time, and the UR min-ε version in O(n + mlogm) time, where m < n is the number of peaks of f. Our algorithms are based on new geometric observations and interesting techniques.
06/2010: pages 200-211;
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ABSTRACT: Heterogeneous dumbbell-like nanoparticles represent an important type of composite nanomaterial that has attracted growing interest. Here we report a general approach to noble metal−metal oxide dumbbell nanoparticles based on seed-mediated growth. Metal oxides are grown over the presynthesized noble metal seeds by thermal decomposition of metal carbonyl followed by oxidation in air. The as-synthesized dumbbell nanoparticles have intrinsic epitaxial linkage between the metal and the oxide, providing enhanced heterojunction interactions. Moreover, the properties of one component are readily modified by the other in these nanoparticles, as demonstrated by the enhanced catalytic activity toward CO oxidation of such dumbbell nanoparticles in comparison with their counterparts prepared by conversional methods. The heterojunction effects provided in such nanostructures thus offer another degree of freedom for tailoring material properties. The developed synthetic strategy could also be generalized to other systems and thus represent a general approach to heterogeneous nanomaterials for various functional applications.
04/2010;
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ABSTRACT: A dosimetric comparison of multiple static-field intensity-modulated radiation therapy (IMRT), multiarc intensity-modulated arc therapy (IMAT), and single-arc arc-modulated radiation therapy (AMRT) was performed to evaluate their clinical advantages and shortcomings.
Twelve cases were selected for this study, including three head-and-neck, three brain, three lung, and three prostate cases. An IMRT, IMAT, and AMRT plan was generated for each of the cases, with clinically relevant planning constraints. For a fair comparison, the same parameters were used for the IMRT, IMAT, and AMRT planning for each patient.
Multiarc IMAT provided the best plan quality, while single-arc AMRT achieved dose distributions comparable to those of IMRT, especially in the complicated head-and-neck and brain cases. Both AMRT and IMAT showed effective normal tissue sparing without compromising target coverage and delivered a lower total dose to the surrounding normal tissues in some cases.
IMAT provides the most uniform and conformal dose distributions, especially for the cases with large and complex targets, but with a delivery time similar to that of IMRT; whereas AMRT achieves results comparable to IMRT with significantly faster treatment delivery.
International journal of radiation oncology, biology, physics 04/2010; 76(5):1554-62. · 4.59 Impact Factor
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Algorithm Theory - SWAT 2010, 12th Scandinavian Symposium and Workshops on Algorithm Theory, Bergen, Norway, June 21-23, 2010. Proceedings; 01/2010
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01/2009;
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Int. J. Found. Comput. Sci. 01/2009; 20:361-377.
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ABSTRACT: Arc-modulated radiation therapy (AMRT) is a novel rotational intensity-modulated radiation therapy (IMRT) technique developed for a clinical linear accelerator that aims to deliver highly conformal radiation treatment using just one arc of gantry rotation. Compared to fixed-gantry IMRT and the multiple-arc intensity-modulated arc therapy (IMAT) techniques, AMRT promises the same treatment quality with a single-arc delivery. In this paper, we present a treatment planning scheme for AMRT, which addresses the challenges in inverse planning, leaf sequencing and dose calculation. The feasibility and performance of this AMRT treatment planning scheme have been verified with multiple clinical cases of various sites on Varian linear accelerators.
Physics in Medicine and Biology 11/2008; 53(22):6291-303. · 2.83 Impact Factor
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ABSTRACT: Dose calculations for radiation arc therapy are traditionally performed by approximating continuous delivery arcs with multiple static beams. For 3D conformal arc treatments, the shape and weight variation per degree is usually small enough to allow arcs to be approximated by static beams separated by 5 degrees -10 degrees . But with intensity-modulated arc therapy (IMAT), the variation in shape and dose per degree can be large enough to require a finer angular spacing. With the increase in the number of beams, a deterministic dose calculation method, such as collapsed-cone convolution/superposition, will require proportionally longer computational times, which may not be practical clinically. We propose to use a homegrown Monte Carlo kernel-superposition technique (MCKS) to compute doses for rotational delivery. The IMAT plans were generated with 36 static beams, which were subsequently interpolated into finer angular intervals for dose calculation to mimic the continuous arc delivery. Since MCKS uses random sampling of photons, the dose computation time only increased insignificantly for the interpolated-static-beam plans that may involve up to 720 beams. Ten past IMRT cases were selected for this study. Each case took approximately 15-30 min to compute on a single CPU running Mac OS X using the MCKS method. The need for a finer beam spacing is dictated by how fast the beam weights and aperture shapes change between the adjacent static planning beam angles. MCKS, however, obviates the concern by allowing hundreds of beams to be calculated in practically the same time as for a few beams. For more than 43 beams, MCKS usually takes less CPU time than the collapsed-cone algorithm used by the Pinnacle(3) planning system.
Physics in Medicine and Biology 10/2008; 53(17):4733-46. · 2.83 Impact Factor
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ABSTRACT: Deoxy-liquefaction runs were performed at final temperatures of 350, 400, 450, and 500 °C, with only 10 wt % distilled water as medium. The influence of the final temperature on the properties of biopetroleum obtained from sunflower shell samples (with kernels 5 wt %) via deoxy-liquefaction was examined in relation to the yield and distribution of products (i.e., gas, solid, liquid), especially the compositions of oil products. Furthermore, the liquid oil with a maximum yield and H/C molar ratio of 1.99 and higher heating value (HHV) of 46.9 MJ/kg was obtained at 450 °C. The biopetroleum analyzed by gas chromatography−mass spectrometry (GC−MS) with the National Institute of Standards and Technology (NIST) 98 MS library was mainly composed of benzene derivatives, phenolic derivatives, and alkanes (C7−C19). What is special is that the content of (Z,Z)-9,12-octadecadienoic acid (RT = 21.26 min), which came from the few sunflower kernels decreased from 21.32% at 350 °C to zero at 500 °C. This suggested that deoxy-liquefaction in a closed system could realize not only the deoxygenation of biomass but the deoxygenation of linoleic acid by controlling the final temperature. Moreover, the biopetroleum obtained can be upgraded to transport fuel or separated for chemical products.
08/2008;
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ABSTRACT: Intensity-modulated arc therapy (IMAT) is a rotational IMRT technique. It uses a set of overlapping or nonoverlapping arcs to create a prescribed dose distribution. Despite its numerous advantages, IMAT has not gained widespread clinical applications. This is mainly due to the lack of an effective IMAT leaf-sequencing algorithm that can convert the optimized intensity patterns for all beam directions into IMAT treatment arcs. To address this problem, we have developed an IMAT leaf-sequencing algorithm and software using graph algorithms in computer science. The input to our leaf-sequencing software includes (1) a set of (continuous) intensity patterns optimized by a treatment planning system at a sequence of equally spaced beam angles (typically 10 degrees apart), (2) a maximum leaf motion constraint, and (3) the number of desired arcs, k. The output is a set of treatment arcs that best approximates the set of optimized intensity patterns at all beam angles with guaranteed smooth delivery without violating the maximum leaf motion constraint. The new algorithm consists of the following key steps. First, the optimized intensity patterns are segmented into intensity profiles that are aligned with individual MLC leaf pairs. Then each intensity profile is segmented into k MLC leaf openings using a k-link shortest path algorithm. The leaf openings for all beam angles are subsequently connected together to form 1D IMAT arcs under the maximum leaf motion constraint using a shortest path algorithm. Finally, the 1D IMAT arcs are combined to form IMAT treatment arcs of MLC apertures. The performance of the implemented leaf-sequencing software has been tested for four treatment sites (prostate, breast, head and neck, and lung). In all cases, our leaf-sequencing algorithm produces efficient and highly conformal IMAT plans that rival their counterpart, the tomotherapy plans, and significantly improve the IMRT plans. Algorithm execution times ranging from a few seconds to 2 min are observed on a laptop computer equipped with a 2.0 GHz Pentium M processor.
Medical Physics 02/2008; 35(1):61-9. · 2.83 Impact Factor
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Algorithms - ESA 2008, 16th Annual European Symposium, Karlsruhe, Germany, September 15-17, 2008. Proceedings; 01/2008
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Int. J. Comput. Geometry Appl. 01/2008; 18:63-106.
