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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
561

Studies on the Chemical Constituents from the Formosan Corals Rumphella antipathies and Echionmuricea sp.

Chung, Hsu-Ming 14 February 2012 (has links)
In the interest of identifying natural substances from marine invertebrates collected off the waters of Taiwan, we have searched the bioactive metabolites from the organic extracts of gorgonian corals Rumphella antipathies and Echinomuricea sp. This study had led to the isolation of thirty compounds (1¡V30), including nine new caryophyllane-related metabolites, rumphellaones A (1), B (2) and C (3), rumphelloic acids A (4) B (5) and C (6), rumphellolides J (7), K (8) and L (9), five new clovane-related metabolites, rumphellclovanes A (12), B (13), C (14), D (15) and E (16), two new disesquiterpenoid dimers, rumphelladimers A (24) and B (25), eight new natural products, (8R,9R)-isocaryolane-8,9-diol (10), 4£],8£]-epoxycaryophyllan-5-ol (11), 9£\-hydroxyclovan-2-one (17), 2£]-hydroxyclovan-9-one (18), clovan-2,9-dione (19), 2£]-acetoxyclovan-9£\-ol (20), 9£\-acetoxyclovan-2£]-ol (21) and 2£],9£]-dihydroxyclovane (22), along with a known compound, clovan-2£],9£\-diol (23) from Rumphella antipathies. In addition, three new labdane-, halimane-, and clerodane-related metabolites, echinolids A (26), B (27) and C (28), a new sesquiterpenoid natural product, (7S,10R)-(+)-10,11-epoxycurcuphenol (29), along with a known compound, (+)-curcuphenol (30) were also found in Echinomuricea sp. The structures of metabolites 1¡V30 were established by spectroscopic methods and by comparison of the spectral data with those of related known compounds. The absolute configurations of clovane-type compounds were determined using a modified Mosher¡¦s method for 23. The biosyntheses of compounds 1¡V5 and 12 were proposed. In the biological activity experiments, compounds 5 and 19 displayed significant inhibitory effects on superoxide anion generation and elastase release by human neutrophils in response to FMLP/CB. Compounds 24 and 27 displayed significant inhibitory effects on elastase release by human neutrophils. Compound 27 was found to exhibit inhibition against the growth of DLD-1 (human colon adenocarcinoma) and Lovo (human colorectal adenocarcinoma) tumor cells.
562

Reproductive ecology of Cardisoma carnifex (Brachyura) in Hengchun Peninsula, Taiwan

Chen, Tzu-chieh 04 July 2012 (has links)
The aim of this study was to investigate the reproductive ecology including fecundity, reproductive season, timing of larval release, evaporative water loss during reproductive migration, and the salinity tolerance of first zoeal stage of Cardisoma carnifex in Houwan, Hengchun Peninsula. The average carapace width of ovigerous females was 70.5 ¡Ó 6.57 mm, with a size range of 56.0-93.7 mm. Fecundity intimates increased with size and the number of hatched larvae from individual female varied from 90,000 to 490,000. The reproductive season of C. carnifex began at the onset of the rainy season and ends approximately at the end of that season. The reproductive season was from June to Oct. in 2009 and May to Sept. in 2010. The peaks of larval release occurred in July in 2009, 2010. Some females had the capacity in spawning twice during a reproductive season. Ovigerous females releasing larvae synchronously. The relationship between larval release timing and environmental cycle is listed in decreasing order of importance: diel rhythm, semilunar rhythm, tidal amplitude rhythm, and a low correlation was found with the tidal rhythm. Ovigerous females of C. carnifex started to release larvae after the new and full moon, lasting for 6-8 days with peaks occurring 4-6 days after the new and full moon. The peaks of larval release occurred within 2-3 hours after the sunset time (i.e., between 1930H and 2130H). This species exhibits different larval release timing and behavior compare to other species of Gecarcinidae; ovigerous females of gecarcinid crabs follow a lunar rhythm but C. carnifex follow a semilunar rhythm. More than half of the ovigerous females stayed in the water for up to 10 min (average 5.5 ¡Ó 2.87 min) and could move to deep water (i.e., 120 cm) to release their larvae. A few females even released their larvae in the freshwater environment. For C. carnifex, a mean of 15¢H of its original weight was lost by the time they died and the osmolality of the hemolymph is 856 mOsm kg-1. Compare with the hemolymph osmolality of ovigerous females (694 ¡Ó 6.3 mOsm kg-1), the results indicated that the ovigerous females at Houwan may not experience severe water loss during larval release migration. The first zoeal stage of C. carnifex could not survive in the freshwater, all larvae died within 2 hours. However, at salinities large than 5‰, most larvae could survive for more than 3 days. The results show first zoeal stage of C. carnifex had adapted to the low salinity in the estuary.
563

Do More Transparent Corporate Actions Following a Restatement Influence the SEC's Decision to Issue an Enforcement Action?

Files, Rebecca Lynn 2009 August 1900 (has links)
This study examines whether corporate transparency about a restatement influences the Securities and Exchange Commission's (SEC) decision to issue an enforcement action. I consider corporate transparency to be higher when firms initiate an independent investigation into the restatement, display the restatement in a more prominent press release location, and/or report the restatement in a more visible SEC filing (i.e., Form 8-K). My sample of restatement observations spans nine years, 1997-2005, and is taken from the databases compiled by the General Accounting Office. For each restatement observation, I hand-collect information on SEC enforcement actions from the SEC's website and information on corporate transparency from company press releases and SEC filings. In order to determine the influence of corporate transparency, I develop a model predicting which restatement firms will be sanctioned by the SEC that includes measures of restatement severity, restatement characteristics, firm characteristics, and all three measures of corporate transparency. I find that, on average, greater restatement transparency increases the likelihood of an SEC sanction. This result is strongest before the Sarbanes-Oxley Act of 2002 (SOX), where all three proxies for corporate transparency are positive and significant predictors of SEC enforcement actions. After SOX, however, more visible SEC filings decrease the likelihood of an SEC sanction, suggesting that the SEC rewards this type of transparent behavior. In addition, the SEC also rewards corporate transparency by reducing monetary penalties when an enforcement action is issued. These results extend prior research (Bowen et al. 2005; Files et al. 2008; Gordon et al. 2008; Myers et al. 2008) by providing the first evidence on how corporate transparency affects the SEC's decision to issue an enforcement action. The results may be useful to managers of restating firms and academics researching SEC enforcement actions.
564

Modified Acrylic Hydrogels As Controlled Release Systems

Pinardag, Fatma Esra 01 May 2006 (has links) (PDF)
In this study, pH-sensitive poly(acrylamide-co-acrylic acid) hydrogels were synthesized as controlled release systems in the presence of N,N-methylene bisacrylamide as crosslinker and ammonium persulfate as initiator. A set of hydrogels were used in the form they were prepared. One set of hydrogels were prepared as porous networks by incorporating sodium chloride into the reaction medium and then leaching of it after the completion of polymerization reaction. Two sets of hydrogels were modified by argon-plasma at different discharge powers. Hydrogels were characterized by 13C-NMR, XPS, SEM, ATR-FTIR, ESR as well as equilibrium degree of swelling (EDS) and contact angle measurements. Prepared hydrogels were loaded with a model antibiotic, ciprofloxacin-HCl (CPFX), and in-vitro release of CPFX from hydrogel matrices were examined in buffer solutions of varying pH values. There are two factors determining the release rates of CPFX / one is the pH-dependent solubility of CPFX and the other is EDS of the hydrogel samples. For porous samples drug loading and release rates were higher when compared to the control samples and CPFX solubility dominated over release kinetics. Plasma treatment resulted in prolonged release rates in acidic medium.
565

Simulation Of A 1-d Muscle Model In Simulink

Zeren, Zekai Uygur 01 December 2007 (has links) (PDF)
The most basic property of a muscle is its ability to contract and produce force when stimulated. A muscle is mainly composed of cells consisting of myofibrils with its basic unit called as a sarcomere. A sarcomere is composed of actin and myosin responsible for the muscle contraction. The Hill-type muscle model is the most commonly used model to simulate the behavior of a muscle. A muscle can produce its maximum force at isometric conditions. The level of force produced in the muscle is determined by the the frequency of the signals from the CNS. The force production is also a function of force-muscle current velocity and force-muscle current length relations. A muscle contains two types of sensors / i.e. muscle spindle and golgi tendon organ, which give rise to the feedback control of the muscle length and muscle contraction velocity. In this study a 1-D model of a muscle is formed step by step in Simulink. In the models the muscle mechanics has been investigated and the results are compared with the previous works.
566

Psychological Problems Of Prisoners On The Bases Of Their Upon-release Future Expectations And Personality Characteristics: The Importance Of Being Parent And Time Left Before Release

Karaca, Ozlem 01 December 2010 (has links) (PDF)
The main purpose of the study was to obtain an estimate of Upon-Release Future Expectations of prisoners, and to examine the associations between these expectations and prisoners&rsquo / psychological problems. In addition, the effect of being parent, and of time left before release on Upon-Release Future Expectations of prisoners and their psychological problems were aimed to be examined. For these purposes, firstly, Upon-Release Future Expectations Scale was developed, and its reliability was investigated. Positive-Negative Affect Scale, Beck Depression Scale, the Trait Form of State-Trait Anxiety Inventory, and Hopelessness Scale were used to test its criterion-related validity. Then, in order to reveal the associations between the variables, two sets of regression analyses were conducted. In the first regression analysis, age, gender, time left before release, parental status (i.e., being a parent or not), and scores of Rosenbaum&rsquo / s Learned Resourcefulness Scale and Basic Personality Traits Inventory were used as independent variables, and revealed factors of Upon-Release Future Expectations (i.e., Future Conditions, Perceived Risks, and Confidence in Coping) were entered as dependent variables. In the second regression analysis, besides the independent variables of the first analysis, factors of Upon-Release Future Expectations were used as independent variables, and depression, trait anxiety, and hopelessness scores were entered as dependent variables. The results did not reveal a main effect for time left before release and parental status. Both the significant associations and the insignificant associations between the dependent and the independent variables were discussed. The study was conducted with 96 female and 84 male prisoners.
567

Thermosensitive Biodegradable Mpeg-plla Block Copolymers: Syntheses, Characterizations And Applications In Drug Delivery Systems / Synthesis And Properties Of Novel Electrochromic Polythienylpyrrole

Mert, Olcay 01 May 2011 (has links) (PDF)
Syntheses of biodegradable PLLA homopolymers and PLLA-mPEG diblock copolymers for the formation of thermo-sensitive gels were performed. The sol-gel transition temperature of the matrix was adjusted by altering the length of each PEG and LA component. PLLA-mPEG biocompatible copolymers, having appropriate length of each block component, showed sols at around 42-45 oC, suitable for the injection, then a gel with subsequent rapid cooling to body temperature. Topotecan and camptothecin were selected as anti-cancer drugs. Both drugs can easily hydrolyze at physiological conditions (pH=7.4). This causes the loss of its activity, and it turns into inactive toxic carboxylate form from active lactone state. To keep those anti cancer drugs in the lactone form, they were efficiently loaded into PLLA-mPEG gels in different loading ratios. Their stability in gel was fully examined with HPLC and fluorescence spectroscopy. It was found that both drugs were highly stable and in active form in the prepared gels (&gt / 95 %). Then, both release profile of drugs at different loading ratios showed prolonged release over weeks. Mechanistic studies on the stabilization of CPT anti cancer drug with PLLA-mPEG gels were carried out using ATR-FTIR, confocal and optic microscopes. The cytotoxic efficacy of TPT in the PLLA-mPEG platform (PLLA-mPEG-TPT) was evaluated on LLC-1 and 4T1 cancer cell lines by MTT assay. In vivo, the administration of PLLA-mPEG-TPT to the mice bearing breast tumours established with 4T1 cells resulted in a significant reduction in tumour size and better survival percentages. Additionally, stabilization of CPT and TPT with gels may find another application on solid tumors in brain via local injection. A novel conducting polymer was successfully synthesized via electropolymerization of 1-(1H-pyrrol-1-yl)-2,5-di(thiophen-2-yl)-1H-pyrrole. The electrochemical and electro-optical properties of the corresponding polymer, which was the first example of polymer containing 1,1&rsquo / -bipyrrole units, were elaborated using electroanalytical and spectroscopic techniques. Cyclic voltammograms and electrooptical studies showed that the polymer has a stable and well-defined reversible redox process as well as electrochromic behavior. The processable polymer film also possessed a yellowish orange light emitter property.
568

Biopolymer Based Micro/nanoparticles As Drug Carriers For The Treatment Of Skin Diseases

Eke, Gozde 01 April 2011 (has links) (PDF)
Controlled drug delivery systems are becoming increasingly interesting with the contribution of nanotechnology. In the case of transdermal applications the greatest limitation is the highly impermeable outermost layer of the skin, the stratum corneum. One promising method of controlled transdermal drug delivery of the skin therapeutics is the use of nanoparticles as carriers. Encapsulation of the drug, as opposed to classical topical application of creams or emulsions, allows the drug to diffuse into hair follicles where drug release can occur in the deeper layers of the skin. The aim of this study was to develop micro and nano sized carriers as drug delivery systems to achieve treatment for skin conditions like psoriasis, aging or UV damage, caused by radiation or health problems. Two different types of bioactive agents, retinyl palmitate (RP) and Dead Sea Water (DSW), were used by encapsulating in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) carriers. In some tests MgCl2 was used as a substitute for DSW when quantification was needed. Bioactive agent loaded nanospheres and nanocapsules were prepared with o/w and w/o/w methods in low micron (1.9 &micro / m), mid nano (426 nm) and nano (166 nm) sizes. Loading, encapsulation efficiency and release kinetics were studied. The encapsulation efficiency and loading values are low especially for the water soluble agents, DSW and MgCl2. It was observed that the capsules loaded with hydrophilic agents released their content in the first 24 h in aqueous media. The encapsulation efficiency and loading values for RP were higher because of the insolubility of the agent in water. In the in vitro studies carried out with L929 mouse fibroblast cells, the nano sized PHBV capsules were detected in the cytoplasm of the cells. Cell viability assay (MTT) for L929 cells showed a growth trend indicating that the particles were not cytotoxic and the values were close to the controls. Hemolytic activity was examined using human erythrocytes and micro/nanoparticles of PHBV were found to be non hemolytic. In vivo testing with BALB/c mice, nanocapsule penetration revealed that a small amount of nano sized particles penetrated the mice skin, despite the highly impermeable outer skin layer. As a result, PHBV micro/nanoparticles have a significant potential for use as topical drug delivery systems in the treatment of skin diseases.
569

Approximation and Optimal Algorithms for Scheduling Jobs subject to Release Dates

Yu, Su-Jane 30 July 2003 (has links)
In this dissertation, we study the single machine scheduling problem with an objective of minimizing the total completion time subject to release dates. The problem, denoted 1|rj £UCj ,was known to be strongly NP-hard and both theoretically and practically important. The focus of the research in this dissertation is to develop the efficient algorithms for solving the 1|rj|£UCj problem. This thesis contains two parts. In the first part, the theme concerns the approximation approach. We derive a necessary and sufficient condition for local optimality, which can be implemented as a priority rule and be used to construct three heuristic algorithms with running times of O(n log n). By ¡¨local optimality¡¨, we mean the optimality of all candidates whenever a job is selected in a schedule, without considering the other jobs preceding or following. This is the most broadly considered concepts of locally optimal rule. We also identify a dominant subset which is strictly contained in each of all known dominant subsets, where a dominant subset is a set of solutions containing all optimal schedules. In the second part, we develop our optimality algorithms for the 1|rj |£UCj problem. First, we present a lemma for estimating the sum of delay times of the rest jobs, if the starting time is delayed a period of time in a schedule. Then, using the lemma, partially, we proceed to develop a new partition property and three dominance theorems, that will be used and have improved the branch-and-bound algorithms for our optimization approach. By exploiting the insights gained from our heuristics as a branching scheme and by exploiting our heuristics as an upper bounding procedure, we propose three branch-and-bound algorithms. Our algorithms can optimally solve the problem up to 120 jobs, which is known to be the best till now.
570

Antimicrobial packaging system for optimization of electron beam irradiation of fresh produce

Han, Jaejoon 30 October 2006 (has links)
This study evaluated the potential use of an antimicrobial packaging system in combination with electron beam irradiation to enhance quality of fresh produce. Irradiated romaine lettuce up to 3.2 kGy showed negligible (p > 0.05) changes in color, but texture and sensory attributes were less acceptable with increased dose. We established the antimicrobial effectiveness of various active compounds incorporated into the low-density polyethylene (LDPE)/polyamide films to increase radiation sensitivity of surrogate bacteria (Listeria innocua and Escherichia coli). All films showed inhibition zones in an agar diffusion test. In the liquid culture test, the active compounds reduced the specific growth rate and decreased final cell concentration of strains. Films incorporated with active compounds increased the radiation sensitivity of the tested strains, demonstrating their potential to reduce the dose required to control microbial contamination using electron beam technology. The active compounds maintained their antimicrobial activity by exposure to ionizing radiation up to 3 kGy. Antimicrobial activity of LDPE/polyamide films incorporated with transcinnamaldehyde was tested with fresh-cut romaine lettuce. Total aerobic plate counts (APC) and yeast and mold counts (YMC) were determined as a function of dose (0, 0.5, and 1.0 kGy) for 14 days of storage at 4°C. Irradiation exposure significantly lowered APCs of lettuce samples by 1-log CFU/g compared to the non-irradiated controls; however, it only slightly reduced YMCs. The effectiveness of using irradiation with antimicrobial films was enhanced with increased radiation dose and transcinnamaldehyde concentration. Electron beam irradiation up to 20 kGy did not affect the tensile strength and toughness of the polymeric films. The film’s flexibility and barrier properties were significantly improved by exposure to 20 kGy. The addition of an active compound did not affect the tensile strength and barrier properties of the films, but decreased the percent elongation-at-break and toughness, making them slightly more brittle. Ionizing radiation affected the release kinetics of the antimicrobial agent from the packaging material into a model food system. Irradiated films exhibited slower release rates than non-irradiated film by 69%. In addition, release rate was lower at 4ºC by 62.6% than at 21-35ºC. The pH of the simulant solution affected release rate with pH 4 yielding higher rates than pH 7 and 10.

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