• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 750
  • 347
  • 118
  • 70
  • 51
  • 30
  • 28
  • 18
  • 11
  • 10
  • 8
  • 8
  • 8
  • 6
  • 5
  • Tagged with
  • 1809
  • 398
  • 279
  • 258
  • 147
  • 144
  • 114
  • 104
  • 103
  • 93
  • 74
  • 74
  • 72
  • 71
  • 71
  • 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.
1011

Carlin-märkt lax (Salmo salar) och öring (Salmo trutta) : Utsättningar och återfångster i Vänern och Klarälven, 1965-2005

Andersson, Anders January 2011 (has links)
I Vänern, Sverige, fångades årligen ca 75 ton lax och öring av yrkesfisket, sportfisket och fritidsfisket under 1990-talet och början av 2000-talet. Fångsterna av lax och öring verkar ha sjunkit under de senaste åren men det råder stor osäkerhet över fångstuppskattningar. För en ökad förståelse över smolts mortalitet släpps varje år ett visst antal Carlin-märkta laxar och öringar ut i Vänern och Klarälven. Syftet med studien var att sammanställa och analysera databasen för Carlin-märkt lax och öring i Vänern under åren 1965 till 2005. Målet var att åskådliggöra långsiktiga tendenser över återfångster av Carlin-märkt lax och öring i både Vänern och Klarälven samt bedöma om återfångster varierar beroende på utsättningsplats (Vänern eller Klarälven). Microsoft Excel användes för att sammanställa och analysera återfångad och inrapporterad lax och öring från 1965 till 2005. För att bedöma trender för återfångster av de fyra stammarna, Gullspångs- och Klarälvs-, lax och öring, användes linjär regression. Totalt 299 165 Carlin-märkta fiskar fördelade över 388 utsättningsgrupper har släppts ut i Vänern med tillflöden under 40 års tid. Sammanlagt återfångades 14 504 fiskar, vilket motsvarar knappt 5 % av antalet Carlin-märkta och utsläppta fiskar. Återfångsterna har varierat genom åren (<1 % - >20 %), högst var återfångsterna under 1970-och 1980-talet, sedan 1990-talet har de minskat betydligt. Dessa tendenser är liknande för alla fyra stammar. De flesta återfångsterna sker i Vänern. Fisk utsläppt i Vänern återfångas som regel i något högre grad i Vänern än fisk utsläppt i Klarälven. Slutligen framkom att ingen lax eller öring utsläppt i Vänern återfångades i Klarälven. / In Lake Vänern, Sweden, commercial, sport, and subsistence fisheries in the 1990s and the beginning of 2000 caught about 75 tons of salmon and trout. Catches of salmon and trout appeared to have declined in recent years, although there is much uncertainty in catch estimates. In order to better understand smolt-adult mortality, a number of Carlin-tagged salmon and trout are released in Vänern and Klarälven each year. The aim of the study was to assemble and analyze the Carlin-tag database for salmon and trout in Vänern during the years 1965 to 2005. My objectives were to identify long-term trends in tag returns rates in both Vänern and Klarälven, and to assess whether return rates varied by release location (Vänern or Klarälven). Microsoft Excel was used to compile and analyze reported recoveries of Carlin-tagged salmon and trout from 1965 to 2005. Linear regression was used to assess trends in return rates of four stocks, Gullspångsälven and Klarälven salmon and trout. Total 299 165 tagged fish in 388 release groups have been released in Vänern over the 40-year period. Total recaptures were 14 504, which equates to just under 5 % of the number of Carlin-tagged and released fish. Recapture rates have varied throughout the years (<1 % - >20 %), the highest return rates were in the 1970s – 1980s, but they have decreased significantly since the 1990s. These trends are similar for all four stocks. Most of the recaptures occur in the lake, return rates of fish released in the lake are most often caught in the lake than are fish released in Klarälven. Finally, revealed that no salmon or trout that were released in the lake were recaptured in the Klarälven.
1012

Constrained crystallization and depletion in the polymer medium for transdermal drug delivery system

Zeng, Jianming 13 July 2004 (has links)
Transdermal drug delivery systems (TDS) are pharmaceutical devices that are designed to deliver specific drugs to the human body by diffusion through skin. The TDS effectiveness suffers from crystallization in the patch when they are kept in storage for more than two years. It has been reported that there are two types of crystals in the patch: needle and aggregate, and growth of drug crystals in TDS generally occurs only in the middle third of the polymer layer. In our study, fluorescence microscopy, EDS (SEM) and Raman microspectroscopy were used to further characterize the crystals. The results show that the needle crystals most probably contain estradiol and acrylic resin conjugate. The FTIR spectrum of the model sample proved the occurrence of a reaction between estradiol and acrylic resin. Crystal growth in an unstressed matrix of a dissolved crystallizable drug component was simulated using a kinetic Monte Carlo model. Simulation using Potts model with proper boundary condition gives the crystals in the middle of matrix in the higher temperature. Bond fluctuation model is also being implemented to study representative dense TDS polymer matrix. This model can account for the size effect of polymer chain on the crystal growth. The drug release profile from TDS was also studied by simulating the diffusion of drug molecules using Monte Carlo techniques for different initial TDS microstructure. The release rate and profile of TDS depend on the dissolution process of the crystal. At low storage temperature, the grains are evenly distributed throughout the thickness of the TDS patch, thus the release rate and profile is similar to the randomly initiated system. Further work on stress induced crystallization is currently under development. Although the study was specifically done for drug in a polymer medium, the techniques developed in this investigation is in general applicable to any constrained crystallization in a polymer medium.
1013

Developing a Minimally Invasive Sustained Release System for Glioma Therapy

Kao, Chen-Yu 16 November 2007 (has links)
Malignant brain tumor is one of the most lethal forms of cancers. In the United States alone, approximately 20,500 new cases of primary malignant brain and central nervous system tumors are expected to be diagnosed in 2007 with 12,740 deaths estimated. Treatment of malignant brain tumor remains a major challenge despite recent advance in surgery and other adjuvant therapies, such as chemotherapy. The failure of potential effective chemotherapeutics for brain tumor treatment is usually not due to the lack of potency of the drug, but rather can be attributed to lack of therapeutic strategies capable of overcoming blood brain barrier for effective delivery of drug to the brain tumor. In this thesis, we developed a minimally invasive sustained release system for glioma therapy. The present study was initiated in an effort to incorporated Doxorubicin (DOX) loaded PLGA particle into an agarose gel, which can provide a continuous release of DOX locally to the tumor site. DOX, a toposiomearase II inhibitor, is not currently used clinically for brain tumor treatment because when delivered systemically it does not cross BBB. Our hydrogel particle system can overcome this shortcoming of DOX. The results from this study demonstrate that the DOX/PLGA particle gel system can maintain the bioactivity of DOX and sustained release DOX for at least 15 day in vitro. The result of in vivo study showed the DOX/PLGA particle gel treated group had significantly extend the medium survival of 9L glioma bearing rat from 21 days to 29 days. Therefore, the success experience of this local and sustained delivery device might benefit the development of future glioma therapy strategy.
1014

Preparation And Evaluation Of Polymer Based Microcarriers For Hydrophobic Anti-cancer Drugs

Demetci, Demet 01 December 2007 (has links) (PDF)
Chemotherapy is one of the most important treatments for cancer. However, systemic toxicity, drug resistance and unstable kinetics of the drug in the blood are serious problems of chemotherapy. The use of biodegradable polymers for controlled release of anticancer drugs has gained popularity in recent years. Controlled release of drugs from polymeric carriers has some advantages such as improvement in the efficiency of treatment, reduction in systemic toxicity and prevention of the drug resistance that is developed by the cancer cells. In this study, poly(D,L-lactide-co-glycolide) microparticles were used as carriers for the controlled release of all-trans-Retinoic acid, tamoxifen, tamoxifen citrate and idarubicin. It was aimed to prepare a drug carrier system for controlled release of hydrophobic anticancer drugs. The empty and drug loaded poly (D,L-lactide-co-glycolide) microparticles were prepared by solvent extraction/evaporation technique with single emulsion (oil/water). Optimized microparticles were characterized by using inverted light microscopy and scanning electron microscopy to examine their morphology and sizes. Drug content of microparticles and the amount of released drug were determined spectrophotometrically. In vitro toxicity of the microparticles on MCF-7 human breast cancer cells was investigated. It was revealed that the microparticles were smooth and spherical in shape. Their sizes differed in the range of 2-20 &micro / m. atRA-loaded microparticles showed approximately 90% encapsulation efficiency and it was confirmed that changing in drug/polymer ratio affected the extend of drug content. Increase in drug content caused a slower release pattern. Moreover, although the empty microparticles caused some toxicity, atRA-loaded PLGA microparticles showed slight cell growth inhibition.
1015

A Theoretical Analysis Of Fire Development And Flame Spread In Underground Trains

Musluoglu, Eren 01 August 2009 (has links) (PDF)
The fire development and flame spread in the railway carriages are investigated by performing a set of simulations using a widely accepted simulation software called &amp / #8216 / Fire Dynamics Simulator&amp / #8217 / . Two different rolling stock models / representing a train made up of physically separated carriages, and a 4-car train with open wide gangways / have been built to examine the effects of train geometry on fire development and smoke spread within the trains. The simulations incorporate two different ignition sources / a small size arson fire, and a severe baggage fire incident. The simulations have been performed incorporating variations of parameters including tunnel geometry, ventilation and evacuation strategies, and combustible material properties. The predictions of flame spread within the rolling stock and values of the peak heat release rates are reported for the simulated incident cases. In addition, for a set of base cases the onboard conditions are discussed and compared against the tenability criteria given by the international standards. The predictions of heat release rate and the onboard conditions from the Fire Dynamics Simulator case studies have been checked against the empirical methods such as Duggan&amp / #8217 / s method and other simulation softwares such as CFAST program.
1016

Vancomycin Containing Plla Delivery System For Bone Tissue Biocompatibility And Treatment Of Implant Related Chronic Osteomyelitis

Uysal, Berna 01 September 2009 (has links) (PDF)
Osteomyelitis is an infection of bone or bone marrow, usually caused by pyogenic bacteria. It can cultivate by hematogen way or it can cultivate by the help of local soft tissue infection. Osteomyelitis often requires prolonged antibiotic therapy and surgery. But for therapy / antibiotic must reach to effective dose in the bone. So that / for prevention and treatment of osteomyelitis controlled antibiotic release systems can be used. These systems have been developed to deliver antibiotics directly to infected tissue. As a carrier material / polymers are widely use. Polymer can be biodegradable or non biodegradable. The advantage of biodegradable polymers is / you do not need a second surgery for the removal of the carrier material from the body. In this study / vancomycin loaded PLLA/TCP composites were developed and characterized to treat implant related chronic osteomyelitis in experimental rat osteomyelitis model. Some of the composites were prepared by coating the vancomycin loaded composites with PLLA to observe the difference between the coated and uncoated composites. Also, some composites were developed free from the vancomycin to determine the biocompatibility of the composite for the bone tissue. The coating extended the release of the vancomycin up to 5 weeks and changed the surface morphology of the composites. According to the cell culture studies, vancomycin loaded PLLA/TCP composites promoted cell adhesion, cell proliferation and mineralization so / the composite was biocompatible with bone tissue. Radiological and microbiological evaluations showed that vancomycin loaded and coated vancomycin loaded PLLA/TCP composites inhibited MRSA proliferation and treat implant related chronic osteomyelitis.
1017

Experimental And Numerical Studies On Fire In Tunnels

Celik, Alper 01 September 2011 (has links) (PDF)
Fire is a complex phenomenon including many parameters. The nature of fire makes it a very dangerous and hazardous. For many reasons the number of tunnels are increasing on earth and fire safety is one of the major problem related to tunnels. This makes important to predict and understand the behavior of fire, i.e., heat release rate, smoke movement, ventilation effect etc. The literature includes many experimental and numerical analyses for different conditions for tunnel fires. This study investigates pool fire of three different fuel sources: ethanol, gasoline and their mixture for different ventilation conditions, different geometries and different amounts. Combustion gases and the burning rates of the fuel sources are measured and analyzed. The numerical simulation of the cases is done with Fire Dynamics Simulator (FDS), a CFD code developed by NIST.
1018

Order Driven Flexible Shop Management

Bulut, Aykut 01 July 2011 (has links) (PDF)
The difficulties in responding to variation in product order mixes and load levels effectively in make to order are known. Most of the existing approaches consider releasing jobs to the shop (input control), changing capacity levels (output control) in a controlled way, order acceptance with different definitions of work load and due date assignment. Controlling the processes, routing options and the order accepting capacity with various tool combinations that will decrease tool loading are not considered properly. However the manufacturing flexibility provided by the computer numerically controlled (CNC) machines, provides both part variety and due date achievement given a reasonable extra capacity. Positive effects of flexibility on the due date achievement of the make to order is shown with a variety of experimental and field studies leaving little doubt. However taking flexibility only as a strategic issue and not considering it as a means of planning and management in either the short term or medium term decisions have been commonplace practice. In this study, benefits of providing three kinds of flexibility, considering order pool and acceptance probability of the new arrivals in a periodic setting, is the focal issue. If the required flexible environment is provided, the necessity to make a detailed job loading, route planning and scheduling will be reduced to a low level and a high shop congestion and due date achievement will be realized simultaneously. A typical realistic shop with a scaled part mix is assumed in the flexibility management modeling and simulation experiments are conducted applying periodical flexibility planning approach. These experiments briefly support the ideas that worth of anticipation is more than plain expectations and flexibility improves robustness.
1019

Preparation And Characterization Of Biodegradable Composite Systems As Hard Tissue Supports: Bone Fillers, Bone Regeneration Membranes And Scaffolds

Aydemir Sezer, Umran 01 February 2012 (has links) (PDF)
In tissue engineering applications, use of biodegradable and biocompatible materials are essential. As the tissue regenerate itself on the material surface, the material degrades with enzymatic or hydrolytic reactions. After a certain time, natural tissue takes the place of the artificial support. Poly(&epsilon / -caprolactone) (PCL) is one of the preferable polymers used in the restoration of the bone defects due to its desirable mechanical properties and biocompatibility. Addition of inorganic calcium phosphate particles in PCL structures can improve the mechanical properties as well as osteoconductivity / and presence of an antibiotic can prevent infection that may occur at the defect site. In this study, three forms of biodegradable hard tissue supports which are bone fillers, bone regenerative membranes and 3D scaffolds were designed and prepared. As biodegradable bone fillers, composite microspheres containing gelatin and &beta / -tricalcium phosphate (&beta / -TCP) were prepared and characterized. Synthesized &beta / -TCP particles were coated with gelatin at different weight ratios and the effects of &beta / -TCP/Gelatin ratio on the morphology of the microspheres were evaluated. Also, a model antibiotic, gentamicin, was loaded to these microspheres and release behaviours of the drug and its antibacterial effect on E.Coli was determined. The selected composition of these microspherical bone fillers were used as additives in the preparation of bone regenerative membranes and scaffolds. For this purpose, microspheres were added into PCL solution and processed by either solvent casting or freeze-drying in order to prepare bone regenerative membranes or scaffolds, respectively. For every material, the ratio of constituents (microsphere and PCL) was altered in order to obtain optimum properties in the resulted hard tissue support structure. The effects of the ratio of the microspheres to PCL in terms of morphological, mechanical and degradation properties of composite films, as well as in vitro antibiotic release and antibacterial activities against E.Coli and S.Aureus were investigated. For scaffolds, the effects of the ratio of the microspheres to PCL on the morphological, mechanical, pore size distribution, degradation properties and in vitro antibiotic release were examined.
1020

Spatial and temporal distribution of latent heating in the South Asian monsoon region

Zuluaga-Arias, Manuel D. 12 November 2009 (has links)
Information from the TRMM-CSH and TRMM-2A12 datasets is used to examine the four-dimensional latent heating (LH) structures over the Asian monsoon region between 1998 and 2006. High sea surface temperatures, ocean-land contrasts and complex terrain produce large precipitation and atmospheric heating rates whose spatial and temporal characteristics are relatively undocumented. Analyses identify interannual and intraseasonal LH variations, with a large fraction of the interannual variability induced by internal intraseasonal variability. Also, the analyses identify a spatial dipole of LH anomalies between the equatorial Indian Ocean and the Bay of Bengal regions occurring during the summer active and suppressed phases of the monsoon intraseasonal oscillation. Comparisons made between the TRMM-CSH and TRMM-2A12 datasets indicate significant differences in the shape of the vertical profile of LH. Comparison of TRMM-LH retrievals with sounding budget observations made during the South China Sea Monsoon experiment shows a high correspondence in the timing of positive LH episodes during rainy periods. Negative values of LH, associated with radiative cooling and with higher troposphere cooling from non-precipitating clouds, are not captured by any of the TRMM datasets. In summary, LH algorithms based on satellite information are capable of representing the spatial and temporal characteristics of the vertically integrated heating in the Asian monsoon region. The TRMM-CSH presents better performance than TRMM-2A12. However, the vertical distribution of atmospheric heating is not captured accurately throughout all different convective phases. It is suggested that satellite derived radiative heating/cooling products are needed to supplement the LH products in order to give an overall better depiction of atmospheric heating.

Page generated in 0.0363 seconds