To see the other types of publications on this topic, follow the link: Boran.
Dissertations / Theses on the topic 'Boran'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Boran.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Böhlke, Steffen. "Untersuchungen zur Borflüchtigkeit bei der Einspeisung von Bor in SWR-Brennelemente bei transienten Kernzuständen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-37939.
Full textAbstract:
In Siedewasserreaktoren ist ein Boreinspeisesystem diversitär wirkend zur Reaktorschnellabschaltung installiert. Dieses System garantiert, dass der Reaktor beim Versagen des Schnellabschaltesystems in einen unterkritischen Zustand überführt werden kann. Der aufgrund der Nachzerfallsleistung entweichende Dampf trägt jedoch ständig einen Teil des eingespeisten Bors in Form von Borsäure mit sich. Da dieser Prozess bisher nicht quantifiziert wurde, ist somit das Eintreten einer Rekrititkalität während der Transiente ohne weitere Untersuchungen nicht auszuschließen. In der vorliegenden Arbeit erfolgt die Erstellung einer fundierten Datenbasis zur Quantifizierung des Borverlusts an verschiedenen Betriebspunkten. Dazu stehen nach vorheriger Konstruktion und Inbetriebnahme zwei Versuchsanlagen zur Verfügung, ein Versuchsautoklav und der Siedewasserreaktor-Simulator BORAN. Das in diesen Versuchsanlagen enthaltene und als Kühlmedium genutzte entionisierte Wasser wird wie bei einem Siedewasserreaktor mit einer hochkonzentrierten Lösung der Borverbindung Dinatrium-Pentaborat-Dekahydrat versetzt. Für weiterführende Untersuchungen findet auch Borsäure Verwendung. Die Bestimmung des Borgehalts der Kondensate des entwichenen Dampfes erfolgt mit Massenspektrometrie mit induktiv gekoppeltem Plasma (ICP-MS). Die durch Variation von Borkonzentration, Temperatur, pH-Wert und Volumendampfgehalt erzeugten Messdaten fließen in einem Flüchtigkeitsmodell in Form einer empirischen Gleichung zusammen, welches in den Thermohydraulikcode ATHLET implementiert wird. Experimente am SWR-Simulator BORAN und entsprechende Rechnungen mit dem modifizierten Code ATHLET von Langzeit-Deborierungstransienten bei unterschiedlichen Randbedingungen bestätigen das Flüchtigkeitsmodell. Gleichzeitig erfolgt mittels dieser Experimente die Validierung des Modells im ATHLET mit hinreichender Genauigkeit. Mit den Ergebnissen aus Rechnungen und Experimenten wird das Boreinspeisesystem in seiner aktuellen Konfiguration bewertet und mit zukünftigen Konzepten verglichen. Schlussendlich erfolgt der Nachweis, dass die Funktionalität des Boreinspeisesystem aus dem Blickwinkel der durchgeführten Analysen, trotz der nachgewiesenen Borflüchtigkeit, die Forderungen der KTA 3103 erfüllt und aufgrund der nachgewiesenen Borflüchtigkeit binnen der ersten beiden Stunden der Transiente keine Rekritikalität verursacht wirdIn boiling water reactors a boron injection system as an alternative system is installed to guarantee that the reactor shut down in case of a total or partial ATWS accident. Because of the heat generated by the fission products after shutting down a part of the injected boron is evaporated as boron acid. This process is not characterized quantitatively yet. This is the reason that the incidence of recriticality during a transient cannot be excluded without further research. In the following studies a funded database quantifying the loss of boron is established. The volatility of the boron solution was measured by experiments in a small autoclave and in a boiling water reactor simulator called BORAN after construction. The deionised water used as coolant in the facilities will be enriched with boron by a high concentrated solution of Disodium-Pentaborate-Decahydrate. The measurement of the boron concentration in the condensates of the exhausted vapour is carried out by inductively-coupled-plasma mass-spectrometry (ICP-MS). For additional analysis boron acid is also used. The boron concentration in the vapour mainly depends on the temperature and void fraction of the two-phase-flow. This volatility model in form of an empiric equation is implemented in the thermo hydraulic ATHLET-code. Furthermore the reason of the volatility of the analysed solutions will be discussed within a chemical and physical background. Experiments at the BORAN facility and corresponding calculation with the modified ATHLET-code of long time deboration transients with different boundary conditions prove the volatility model. Thereby the code will be validated with sufficient accuracy. The modified code with an adapted Input-Dataset provides the possibility to calculate transients with the loss of boron. With the consideration of the volatility the demand of the KTA-rule 3103 on the Boron injection system is also grantable
2
Holschumacher, Dirk [Verfasser]. "Diaminocyclopropenylidene und frustrierte Carben/Boran-Lewis-Paare / Dirk Holschumacher." München : Verlag Dr. Hut, 2011. http://d-nb.info/1010446762/34.
Full text
3
Kios, D. K. (David Kiprotich). "Application of DNA markers in parentage verification of Boran cattle in Kenya." Diss., University of Pretoria, 2011. http://hdl.handle.net/2263/27627.
Full textAbstract:
Boran cattle provide livelihood to thousands of households in the arid and semi arid lands of Kenya. The Kenya Boran cattle breeders’ society (KBCBS) is actively involved in the improvement of the breed. Due to their superior adaptive and productive traits in comparison to other indigenous breeds of cattle, they have also become a popular choice for breeders in Eastern and Southern Africa. Their continued genetic improvement through progeny and performance testing is critical and accurate pedigree records are paramount. Pedigree records of four stud herds were evaluated for accuracy using 11 microsatellite markers on 178 samples. The microsatellite markers had a combined probability of exclusion (CPE) of 0.9997. The dam misidentification rate was 0 to 5% and that of the sires ranged from 4.3 to 80% between the four stud herds. 4,456 Boran pedigree records from Kenya stud book for the four participating stud herds were analysed for inbreeding. The average generation interval was 6.8 years and the estimated inbreeding coefficient was unexpectedly low (0.0023), probably due to incomplete records. The high rate of mispaternity will lead to low response to selection and increased inbreeding. The use of DNA markers for parentage assignment will improve the accuracy of the pedigree records. This will enhance the accuracy of selection, increase the rate of genetic gain and improve effective monitoring of inbreeding.Dissertation (MSc)--University of Pretoria, 2011.
Animal and Wildlife Sciences
unrestricted
4
Ochs, Ronald. "Reaktionen von Phenylbis(trimethylsilyl)phosphan mit Verbindungen der dreizehnten, fünfzehnten und sechzehnten Gruppe." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11947817.
Full text
5
Buchheim-Spiegel, Silke. "Reaktionen von (Dimethylamino)bis(trifluormethyl)boran mit Carbenen, Carbenoiden und Heterocumulenen." [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=959140085.
Full text
6
Nicholson, M. J. "The effects of infrequent drinking intervals on the productivity of Boran cattle." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233322.
Full text
7
Rumberia, Rufus Mburea. "The effect of theileriosis on the reproductive function of Boran/Friesian cross heifers." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/29976.
Full textAbstract:
This thesis describes studies that were undertaken to evaluate the effect of T.parva infection on the reproductive function of Boran/Friesian cross heifers. The study was conducted in four separate experiments. In Experiments 1 and 2, the animals were monitored for cyclical status post-infection. In Experiments 3 and 4, the infected animals were divided into two groups: one group was monitored for cyclical status and the other for both cyclical and pregnancy status after exposure to a bull. The reproductive function was assessed by routine monitoring of oestrous behaviour, palpation of the genital reproductive tract per rectum and determination of serum progesterone (P4) concentrations. Further, in view of observed acyclicity in the early work, attempts were made to assess the pituitary response to gonadotrophin releasing hormone (GnRH) in a group of animals (Ch.5) in an attempt to explain partly the mechanisms involved in the impairment. Animals were monitored for the progression of disease by clinical and parasitological responses. Further, subject to death or sacrifice, a macroscopic and histological examination of target and various other organs and tissues was undertaken in an effort to establish the part played by observable pathological changes in the development of impaired reproductive function. In Experiment 1, ten heifers were infected with 1:20 T.parva stabilate while four others remained as uninfected controls. Two of the infected animals died on days 17 and 29. Clinical reactions in the reovered animals ranged from mild to moderate. P4 profiles and ovarian structures revealed that three of eight recovered animals had luteal dysfunction post-infection although two of the three showed clinical oestrus during this particular period. The other five recovered animals cycled regularly. The results from clinical and pathological studies did not indicate any direct adverse effect of infection on reproductive function. All the four controls cycled throughout the study period.
8
Uluca, Boran [Verfasser]. "Solid-State NMR and DNP-Enhanced NMR Studies on Intrinsically Disordered Proteins / Boran Uluca." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2018. http://d-nb.info/1164763237/34.
Full text
9
Widera, Anna Judith [Verfasser], and Hans-Jörg [Akademischer Betreuer] Himmel. "Das Zusammenspiel zwischen Elektronendefizit und Elektronenreichtum in guanidinatstabilisierten Boran-Kationen / Anna Judith Widera ; Betreuer: Hans-Jörg Himmel." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://d-nb.info/1205210547/34.
Full text
10
Abebe, Getachew. "The integrity of the hypothalamic-pituitary-adrenal axis in Boran (Bos indicus) cattle infected with Trypanosoma congolense." Thesis, Brunel University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292991.
Full text
11
Widera, Anna [Verfasser], and Hans-Jörg [Akademischer Betreuer] Himmel. "Das Zusammenspiel zwischen Elektronendefizit und Elektronenreichtum in guanidinatstabilisierten Boran-Kationen / Anna Judith Widera ; Betreuer: Hans-Jörg Himmel." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://d-nb.info/1205210547/34.
Full text
12
Van, Staden Elizabeth. "Effect of different equilibration periods pre-cryopreservation on post-thaw sperm motility in Nguni and Boran bulls." Diss., University of Pretoria, 2010. http://hdl.handle.net/2263/25956.
Full textAbstract:
Compared to natural selection, the use of artificial insemination (AI) and other reproductive technologies rapidly increase the rate of genetic change in any population. In order to achieve success with AI, the semen used to inseminate cows must be of the highest possible quality. When semen is frozen, generally only about 50% of the spermatozoa survive the cryopreservation process. Thus, any factors possibly affecting the survival of spermatozoa through the numerous freezing-thawing steps should be studied, in order to identify the optimal conditions for the survival of spermatozoa. The discovery of protective agents within egg yolk and glycerol was a major milestone in sperm cryopreservation. These agents protect bovine spermatozoa during cooling and freezing procedures and result in increased survival rates. Cryopreservation of spermatozoa has become the most common technique for the preservation of male fertility of genetically superior sires even after their death. Using cryopreserved sperm to artificially inseminate females has become standard practice in commercial dairy cattle herds and the application of this reproductive management tool is also expanding to beef herds worldwide. The use of glycerol as a cryoprotectant for bovine spermatozoa is credited as the reason for the success in bovine semen cryopreservation. The purpose of this research was to quantify the effects of different cooling periods, as well as different glycerol equilibration periods on the post-thaw motility percentages and recovery fractions of semen collected from Boran and Nguni bulls. The research was subdivided into two experiments. In each experiment different cooling and glycerol equilibration times were researched. The first experiment involved shorter cooling times (30, 60, 120 and 240 minutes) with each cooling time followed by several longer equilibration times (4, 5, 6, 7 and 8 h). In the second experiment the cooling and equilibration times from the first experiment were reversed. This resulted in longer cooling times (4, 5, 6, 7 and 8 h) with each cooling time having shorter glycerol equilibration times (30, 60, 120 and 240 minutes). An egg yolk-Tris two-step extender was used in both the experiments. The general trend for the glycerol equilibration periods studied in Experiment 1 was that the resulting overall average post-thaw motility percentage and average recovery fraction increased with longer periods. There was a breed difference when comparing the average post-thaw motility percentages after 4, 5, 6 and 8 h (p<0.05), while the average post-thaw motility percentages also tended to differ after 7 h of equilibration. The general trend observed for equilibration periods used in Experiment 2 was that the average post-thaw motility percentage increased as glycerol equilibration period increased up to 120 minutes, but after 240 minutes of glycerol equilibration, there was a slight decline. The differences in average post-thaw motility percentage after the respective glycerol equilibration periods were not statistically significant. The results of each experiment were used to create a matrix that can be used in practice. The matrix using results from Experiment 1 demonstrated that a cooling period glycerol equilibration period combination of 240 minutes and 7 h resulted in the highest (not significantly different from most other combinations) average post-thaw motility rates. The matrix formed from the results of Experiment 2 demonstrated that an 8 h cooling period combined with a 60 minute glycerol equilibration period yielded the highest (not significantly different from most other combinations), average post-thaw motility percentage.Dissertation (MSc(Agric))--University of Pretoria, 2011.
Animal and Wildlife Sciences
unrestricted
13
Cunningham, Samantha Fern. "Evaluation of F1 cows sired by Brahman, Boran, and Tuli for reproductive and maternal performance and cow longevity." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2512.
Full textAbstract:
Birth (BW) (n = 1,107) and weaning weight (WW) (n = 1,024), pregnancy rate
(PR) (n = 1,255), calf crop born (CCB) (n = 1,232), calf crop weaned (CCW) (n =
1,225), and cow??s weight at palpation (CW) (n = 1,403) were evaluated from 1994 to
2004 in 143 F1 females who were sired by Brahman (B), Boran (Bo), and Tuli (T) bulls
and who were out of Angus and Hereford cows. In 2004, mouth scores (MS) (n = 71)
were assigned to the remaining females. PR, CCB, CCW, CW, and BCS were evaluated
using a model that consisted of sire of dam breed, dam of dam breed, and calf??s birth
year/age of dam as fixed effects. Sire of dam within sire breed of dam and dam within
sire of dam within sire breed of dam were used as random effects. BW and WW were
analyzed using the same model including calf??s gender. Two-way interactions were
tested for significance. Year/age was significant for all traits (P < 0.05). Adjusted
means for BW for calves out of cows by B, Bo, and T sires were 35.66, 35.38, and 35.59
kg respectively, and were not different (P > 0.05). Adjusted means for WW for calves
out of cows by B, Bo, and T sires were 233.4, 220.1, and 208.2 kg respectively, and
were significantly different. For both BW and WW, male calves were heavier (P < 0.05) than females. Adjusted means for PR for females sired by B, Bo, and T bulls were
0.914, 0.945, and 0.920, and were not different (P > 0.05). Adjusted means for CCB for
females sired by B, Bo, and T bulls were 0.890, 0.943, and 0.910 respectfully, and Bo
was higher (P < 0.05) than B. CCW showed the same ranking as CCB with adjusted
means of 0.834, 0.887, and 0.857 for cows by B, Bo, and T bulls, with Bo being higher
(P < 0.05) than B. CW adjusted means, in the fall of 2002, were 594.29, 519.38, and
517.3 kg. B-sired females were heavier (P < 0.05) than Bo- or T- sired cows. More Bo-
(P = 0.013) and B-sired (P = 0.003) cows had solid mouths in 2004 than T-sired cows.
14
Kronig, Sabrina [Verfasser]. "Untersuchungen zu anionischen N-heterozyklischen Carbenen, 2-Alkyliden-1,3,4,5-tetramethylimidazolinen und frustrierten Carben/Boran-Lewis-Paaren / Sabrina Kronig." München : Verlag Dr. Hut, 2012. http://d-nb.info/1028787103/34.
Full text
15
Maiga, Assalia Hassimi. "Comparison of F1 cows sired by Brahman, Boran and Tuli bulls for reproductive, maternal, and cow longevity traits." Thesis, Texas A&M University, 2006. http://hdl.handle.net/1969.1/4890.
Full textAbstract:
Birth weight (BW) (n =1277) and weaning weight (WW) (n = 1090) of calves, pregnancy rate (PR) (n = 1386), calf crop born (CCB) (n = 1386), calf crop weaned (CCW) (n = 1294), cowâÂÂs weight at palpation (CW) (n = 1474) and cow body condition score (BCS) (n = 1473) were evaluated from 1994 to 2006 in 143 F1 cows sired by Brahman (B), Boran (Bo) and Tuli (T) bulls and born to Angus and Hereford cows. Mouth scores (MS) (n = 139) were assigned to the remaining cows in 2004 and 2005. Fixed effects included sire breed of cow, dam breed of cow, and calfâÂÂs birth year/age of cow; random effects included cow and sire of cow. BW and WW were evaluated using the same model and adding gender for both and age for WW. All two-way interactions were tested for significance. CalfâÂÂs birth year/age of dam was significant for all traits (P < 0.05) except WW. BW for calves out of F1 B, Bo and T bulls were 35.08, 34.76 and 34.87 kg, respectively, and were not different. WW differed (P < 0.05) for calves out of F1 B, Bo and T cows (235.87, 221.10 and 208.35 kg, respectively). PR (0.922, 0.955 and 0.936, respectively), CCB (0.881, 0.931, 0.890, respectively), CCW (0.848, 0.898 and 0.869, respectively), did not differ among F1 B, Bo and T cows. CW when cows were 8- or 9-year old were 600.78, 514.63 and 513.14 kg, respectively, for F1 B, Bo and T cows, with those sired by B being heaviest (P < 0.05). BCS for B-, Bo- and T-sired cows were 5.23, 5.48 and 5.18, respectively, with F1 Bo cows having highest scores. Higher MS (P < 0.05) were assigned to Bo and B-sired cows (0.95 and 0.94, respectively) compared to T-sired cows (0.78), when both broken and solid incisors were scored 1, and smooth scored 0. When both smooth and broken were scored 0, and solid were scored 1, higher scores were assigned to B- (0.53) compared to T-sired cows (0.24), the Bo-sired cows being intermediate. Higher reproductive rates were found for Boran-sired cows, but Brahman-sired cows weaned heavier calves.
16
Schellenberg, René. "Hydrierung von Bortrichlorid mit molekularem Wasserstoff in Gegenwart von Aminen als Hilfsbasen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2011. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-68938.
Full textAbstract:
In dieser Arbeit wurde die Möglichkeit untersucht, Bortrihalogenide mit Wasserstoff unter milden Bedingungen (T < 100 °C, p(H2) < 50 bar) zu hydrieren. Um eine Triebkraft für die thermodynamisch ungünstige Reaktion zu erhalten, wurden Amine als Hilfsbasen zugesetzt, welche den bei der Reaktion entstehenden Halogenwasserstoff als Ammoniumsalz binden und damit das Reaktionsgleichgewicht in Richtung der Produkte verschieben. Es wurden dafür verschiedene Amin-Boran bzw. Amin-HCl Addukte synthetisiert und mittels IR, NMR und DSC charakterisiert. Bei den anschließenden Hydrierungsversuchen wurden verschiedene Katalysatoren auf ihre Eignung getestet und weiterentwickelt. Unterstützt wurden die experimentellen Arbeiten durch Berechnungen mit Gaussian 03. IR- und NMR-Spektren vieler Addukte wurden berechnet und freie Reaktionsenthalpien der Hydrierung in Abhängigkeit des verwendeten Amins und Borhalogenids bestimmt. Mögliche Übergangszustände wurden diskutiert und ihre Aktivierungsenergien ermittelt.
17
Gurbuzbalaban, Melis. "Autonomy: Re-appreciation Of Architecture." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605555/index.pdf.
Full textAbstract:
The contradiction between architecture&rsquos &ldquo
autonomy&rdquo
, its existence as an entity with its own &ldquo
disciplinary specificity&rdquo
- and its social &ldquo
engagement&rdquo
, its involvement in culture, ideology and economy, has been the subject of numerous discussions in architectural discourse, initially in Europe and later in North America. It is argued in this thesis that although &ldquo
autonomy&rdquo
and &ldquo
engagement&rdquo
seem contradictory to each other, architecture&rsquo
s &ldquo
critical status&rdquo
is rooted in this contradiction. Autonomy is regarded as one of the essential sides of architecture&rsquo
s dual position. This suggests that the in-between, or in Stanford Anderson&rsquo
s terms, &ldquo
quasi-autonomous&rdquo
status of architecture can only be sustained through its existence as an entity that has a certain degree of autonomy. Autonomy is an agent for architectural discourse to isolate architecture from its involvement in the external reality and increase awareness within the discipline by concentrating on its specific knowledge. Autonomy aids architecture to pretend to be &ldquo
detached&rdquo
while in reality it is &ldquo
engaged&rdquo
. To focus on the autonomous dimension of architecture, to search for architecture&rsquo
s own intrinsic qualities, helps to produce knowledge within the discipline and provides a &ldquo
critical distance&rdquo
for architecture to resist any &ldquo
external authority&rdquo
. Thus this thesis intends to explore the potentials of the conceptualization and problematization of &ldquo
autonomy&rdquo
in architecture and its employment as a critical tool by architectural discourse to re-assess architectural practice. The private house projects designed by Boran Ekinci in Turkey are exemplified and utilized for the re-conceptualization of the term and enable the transfer of the discourse related with autonomy to the local context where the issue hardly gained a popularity. By doing so, both the appreciation of autonomy in general and reappreciation of architecture in Turkey are aimed.
18
Boran-Krüger, Seda [Verfasser], and Arne [Herausgeber] Krueger. "Germany, the Ottoman Empire and the Armenian Question : Dissertation submitted in partial fulfillment of the requirements for the degree of doctor of philosophy in the department of political science and international relations. / Seda Boran-Krueger." Berlin : epubli, 2017. http://d-nb.info/1139936093/34.
Full text
19
Brain, Paul Terence. "Studies of some compounds containing boron-boron bonds." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291091.
Full text
20
Zhu, Xiaojing. "Processability of Nickel-Boron Nanolayer Coated Boron Carbide." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28633.
Full textAbstract:
This dissertation work focuses on the processability improvement of B4C, especially the compaction and sintering improvement of B4C by applying a Ni-B nanolayer coating on individual B4C particles.
A modified electroless coating procedure was proposed and employed to coat nanometer Ni-B layer onto micron-sized B4C particles. The thickness was able to be tuned and controlled below 100 nm. Key parameters, including the amount of nickel source, the amount of the surface activation agent (PdCl2), the amount of the complexing agent (C2H8N2), and the addition rate of the reducing agent (NaBH4) were studied. When the targeted thickness was 5 nm, a continuous and uniform nanolayer coating was obtained with the optimal condition of individual parameter combined.
Reduction of the as-coated B4C powder in a H2-Ar atmosphere was studied between 400-900ºC to reduce the surface oxidesâ Ni2O3 and B2O3. Reduction at 800ºC in hydrogen atmosphere was found to be the most effective condition to remove oxygen in the coating layer, with Ni2B as the reduction product.
Compaction of the as-received, separated and uncoated, and separated with Ni-B coating B4C powders using uniaxial die compaction and combustion driven compaction (CDC) techniques was studied. CDC technique showed the advantage over the traditional uniaxial die compaction by yielding much higher green density and green strength (73% vs. 53.8% green density for the Ni-B coated B4C). Among compacts obtained from the same technique, Ni-B coated B4C compact yielded the densest packing with crack-free compact surface and the highest strength, demonstrating more bonding between B4C particles provided by Ni-B surface coating.
Sintering of the Ni-B coated B4C in an Ar atmosphere between 1150 - 1600ºC with soaking time of 2 hrs and 10 hrs was studied. Liquid phase was found to form during the sintering process. Density measurement showed that the liquid phase Ni-B formed greatly facilitated B4C densification. Considerable density increase and inter-granular connection was achieved when sintered at 1600ºC for 10 hrs. The density enhancement by Ni-B coating was supported by transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) examination which showed that there was B4C species diffusion into liquid Ni-B phase. This liquid phase enhanced the diffusion of B4C species and formed strong bonding between B4C grains by dissolving small B4C particles and sharp edge and corners of B4C particles. Strength test demonstrated that the Ni-B coating dramatically improved the strength of B4C compacts by yielding a much higher strength of the Ni-B coated samples than the uncoated samples (13.97 vs. 1.79 MPa for the uinaxial die compacted samples, 27.03 vs. 2.21 MPa for the CDC samples). Electrical conductivity Ni-B coated B4C samples was also shown to be improved with the electrical resistivity being reduced from infinite for pure B4C samples to 1.8à 10-3 Ω⠢m for the Ni-B coated samples.
This research work has shown that with the Ni-B coating, B4C densification can start at a temperature as low as 1600ºC via a liquid phase sintering process.Ph. D.
21
DeGraffenreid, Allison Lynne. "Studies on boron - nitrogen and boron - gadolinium compounds." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1294835746.
Full text
22
Salman, Solafa. "Développement de nouvelles méthodes de préservation du bois basées sur l'utilisation combinée d'un traitement thermique et de borax." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0005/document.
Full textAbstract:
Les pressions environnementales apparues en France et en Europe au cours des dernières décennies ont considérablement changé les méthodes de protection du bois. Dans ce contexte, le règlement relatif aux produits biocides et la directive relative aux produits biocides conduisent au développement de méthodes de préservation plus soucieuses de l'environnement et à l’intérêt croissant pour des alternatives non biocides comme le traitement thermique ou la modification chimique. Le traitement thermique à des températures de 180 à 220°C conduit à la modification chimique de la structure des différents constituants pariétaux du bois en lui conférant de nouvelles propriétés comme une meilleure résistance aux champignons basidiomycètes et une grande stabilité dimensionnelle. Malgré ces améliorations, la durabilité conférée au bois traité thermiquement demeure insuffisante pour des applications en classes 3 ou 4 dans lesquelles le bois est en contact avec le sol ou est en présence de termites. Par ailleurs, le bore sous forme d’acide borique ou de borax présente des propriétés fongicides et termiticides. Cependant, les produits à base de bore présentent l'inconvénient d'être très facilement lessivables les rendant inutilisables pour des applications en conditions extérieures. Les modifications chimiques réalisées suite à l'imprégnation de solutions à 10% d'anhydride maléique de polyglycérol ou de méthacrylates de polyglycérol ou de résine phénol formaldéhyde avec ou sans borax avant le traitement thermique ont apporté une amélioration des propriétés des bois modifiés thermiquement et surtout une résistance aux termites avec ou sans lessivageEnvironmental pressures appeared in France and in Europe in the last decades have substantially changed the methods for wood protection. In this context the Biocidal Products Regulations and the Biocidal Products Directive lead to the development of more environmentally friendly preservation methods and the growing interest in non-biocidal alternatives such as thermal treatment or chemical modification. Wood heat treatment at temperatures of 180 to 220 °C leads to the chemical modification of wood cell wall polymers conferring new properties to the material like its increased decay resistance and high dimensional stability. Despite these improvements, the durability of wood heat treatment is not sufficient to envisage use class 3 and 4 applications; where the wood is in contact with soil or termites. Moreover, Boron compounds present fungicidal and termiticidal properties. However, boron compounds have the drawback of being very easily leached out from wood making it unusable for applications in outdoor conditions. Wood chemical modification carried by the impregnation of aqueous solutions (10 %) of maleic anhydride polyglycerol adduct or polyglycerol methacrylates or phenol-formaldehyde resin, with or without borax followed by heat treatment at 220°C has shown some improvement of thermally modified wood properties particularly its resistance to termites in case of leach or not
23
Slade, Alexander Mason Electrical Engineering UNSW. "Boron tribromide sourced boron diffusions for silicon solar cells." Awarded by:University of New South Wales. Electrical Engineering, 2005. http://handle.unsw.edu.au/1959.4/21850.
Full textAbstract:
This thesis undertakes the development, characterization and optimization of boron diffusion for silicon solar cells. Heavy diffusions (sheet resistance < 40 Ohm/square) to form a back surface field, and light diffusions (sheet resistance > 100 Ohm/square) to form oxide-passivated emitters were developed. Test structures and solar cells were fabricated to assess uniformity, lifetime and recombination effects due to the light and heavy boron diffusions. It was found that the growth of a thin ~200 ??, thermal oxide, during stabilization ??? immediately prior to the boron diffusion - was required to maintain high lifetime and reduce surface recombination (reducing the emitter saturation current density) for all boron diffusions. The heavy boron diffusion process was incorporated into the single side buried contact solar cell processing sequence. The solar cells fabricated had both boron diffused and Al/Si alloyed P+ regions for comparison. This research conclusively showed that boron diffused solar cells had significantly higher open circuit voltage compared to Al/Si alloyed devices. Fabrication of n-type solar cells, and their subsequent characterization by overlayed secondary electron image and the electron beam induced current map showed that the Al/Si alloy varied in depth from 5 to 25 micrometers deep. Methodology and characterization for light, oxide-passivated boron diffusions are also presented. This study yielded boron diffused emitters (sheet resistance > 100 Ohm/square) with low emitter saturation current. It was observed that this was possible only when the thermal oxidation after the boron diffusion was minimal, less than 1,000 ??. This was due to the segregation effect of boron with oxide, decreasing the surface concentration that in turn decreased the electric field repulsion of electrons from the surface. Device modelling of n-type solar cells is presented where the parameters of the modelling include the results of the light, oxide-passivated boron diffusions. This modelling shows n-type-base material with light oxide-passivated boron diffusion has higher potential conversion efficiency than forming a solar cell from phosphorous diffused p-type material.
24
Yamamoto, Akihiko. "Boron-based organic reactions using boron cyanides and chlorides." 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/143990.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第12293号
工博第2622号
新制||工||1370(附属図書館)
24129
UT51-2006-N978
京都大学大学院工学研究科合成・生物化学専攻
(主査)教授 杉野目 道紀, 教授 檜山 爲次郎, 教授 村上 正浩
学位規則第4条第1項該当
25
Spivack, Arthur J. "Boron isotope geochemistry." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15187.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and Woods Hole Oceanographic Institution, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN
Vita.
Includes bibliographies.
by Arthur J. Spivack.
Ph.D.
26
Taylor, Nicholas. "Borane transfer reactions." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/22027.
Full textAbstract:
Lewis base borane adducts (LB·BH3) constitute a well-known class of molecules with a number of diverse applications, including use as protected phosphines. The kinetics and thermodynamics of borane transfer reactions from a wide range of Lewis base borane complexes have been studied. The data generated has been used both as a quantitative tool to describe the nucleofugality (leaving group ability) of Lewis bases and as a means to improve the efficiency of phosphine borane deprotection reactions. The kinetics of borane transfer from a range of tertiary phosphine borane complexes to a wide range of amines have been determined. All kinetic data obtained, in addition to computational evidence, are consistent with a direct (SN2-like) mechanism, rather than a dissociative (SN1-like) process. The identities of the amine, phosphine and to a lesser extent solvent, impact substantially on the rate and equilibrium of the transfer, which can span several orders of magnitude. In depth structure activity relationships have been explored both for a wide variety of amine nucleophiles and phosphine nucleofuges. Taken as a whole, the data allow informed optimisation of the “deprotection” of a phosphine borane complex from the standpoint of rate or synthetic convenience. Additionally, the kinetics of ethanolysis of tri(o-tolyl)phosphine borane complex have also been studied. Using bridgehead amine quinuclidine as a benchmark, the kinetics of borane transfer from a wide range amine borane adducts have also been determined. Parameterisation of these data, in addition to that obtained for the analogous phosphine borane complexes, has allowed development of a novel nucleofugality scale (NFB) that quantifies the leaving group ability of a wide range of Lewis bases. Additivity in the kinetics across a series R3−nR’nX·BH3 (X = P, N; R/R’ = aryl, alkyl) has led to the formulation of related substituent parameters (nf PB, nfAB) that quantify the nucleofugal influence of a substituent. Using the substituent nucleofugality parameter in concert with additivity provides a mean of calculating ligand nucleofugality (NFB) values for a wide range of Lewis bases that extends far beyond those experimentally derived. Good agreement was found between predicted (using NF B and nFB values) and experimental rates of borane transfer for ligands outside the training set, thus providing a means to predict the relative rate of phosphine borane deprotections. The utility of both parameters was demonstrated through correlations to rates of redox transformations at iridium (bearing phosphine spectator ligands) and MIDA boronate hydrolysis, (MIDA = N-methyliminodiacetic acid). Through these correlations, interesting subtleties in the mechanism of MIDA boronate hydrolysis have been identified.
27
Yapo, Marie Michelle. "Haitian-born mothers raising American-born adolescent daughters." Click here for text online. The Institute of Clinical Social Work Dissertations website, 2005. http://www.icsw.edu/_dissertations/yapo_2005.pdf.
Full textAbstract:
Dissertation (Ph.D.) -- The Institute for Clinical Social Work, 2005.A dissertation submitted to the faculty of the Institute of Clinical Social Work in partial fulfillment for the degree of Doctor of Philosophy.
28
Castro, Susana Patricia. "CHARACTERIZATION OF THE BORON DOPING PROCESSUSING BORON NITRIDE SOLID SOURCE DIFFUSION." NCSU, 1999. http://www.lib.ncsu.edu/theses/available/etd-19990523-142337.
Full textAbstract:
CASTRO, SUSANA PATRICIA. Characterization of the Boron Doping Process UsingBoron Nitride Solid Source DiffusionThe purpose of this research has been to develop an optimum process for the borondoping of implants and polysilicon gates of metal-oxide-semiconductor (MOS) devices.An experimental design was constructed to determine the effects of diffusiontemperature, time, and ambient on characteristics of the doping process. A temperaturerange of 800 to 1000 degrees Celsius was studied with a diffusion time between 10 and60 minutes. Two diffusion ambients were used for doping processes, a pure nitrogenambient and a nitrogen-oxygen gaseous mixture. Device wafers were fabricated, and thetesting of MOS capacitors and van der Pauw test structures was performed to determinethe effect of diffusion conditions on flatband voltage and poly gate doping. Materialscharacterization techniques were used on monitor wafers for each diffusion process todetermine the wafer structure formed for each process and evaluate the effectiveness ofthe deglaze etch. The processes that resulted in the best device characteristics withoutsuffering from significant poly depletion effects and flatband voltage shifts were wafersdoped at 800 degrees Celsius in a pure nitrogen atmosphere for 20 minutes and 45minutes. The presence of oxygen in the atmosphere caused the depletion of boron fromthe Si wafer surface. The formation of the Si-B phase only occurred on devices processedat 1000 degrees Celsius. The deglaze process used in this experiment did not fullyremove this layer, and thus all devices doped at this temperature were seriously degraded.
29
Leenhouts, James Merrell 1968. "Behavior of boron and boron isotopes during uptake by Atriplex canescens." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284177.
Full textAbstract:
This research was conducted to determine the potential for using plants to obtain samples of boron isotopes from groundwater, sod moisture and fracture water. In essence, this work sought to ascertain whether plants can function as in-situ samplers for boron as an environmental isotope. At present, very little is known about the behavior of boron isotopes in plants so this study was designed to reveal any isotopic fractionation that might occur during plant uptake by a specific species under carefully controlled conditions. The relationship between the boron isotope ratios sequestered in the leaves of the species Atriplex canescens and the growth conditions of the plant were investigated using a semi-hydroponic greenhouse experiment. Nutrient boron concentration and solution pH were selected as experimental variables as these parameters span large ranges in nature. In addition, the mechanism through which plants take up anionic nutrients suggests that boron isotope fractionation could occur. The experimental setup was a randomized factorial block design and the plants were provided six different nutrient solutions with pH values ranging from 7.5 to 9.5 and boron concentrations varying from 0.1 mg/L to 10.0 mg/L. Boron concentration in the plant's leaf and stem samples followed expected patterns, with the highest boron amount in the leaves of the plants fed nutrient solution with 10.0 mg/L B. The stern samples of plants fed 0.1 mg/L B contained the least boron. The ratio of boron in plants fed 10.0 mg/L vs. 0.1 mg/L B was far less than the 100:1 ratio of boron in the nutrients, which implies that a component of uptake is actively controlled by the plant. Negative thermal ionization mass spectrometry was employed to analyze the minute amounts of boron extracted from digests of the plant tissues. Statistical tests were utilized to determine that, contrary to the hypothesis, no significant isotopic fractionation occurred during uptake at any treatment pH level. The results of this research indicate that the species Atriplex canescens can provide samples of boron isotopes which closely represent the isotopic signature of the plant's water source.
30
Noguchi, Hiroyoshi. "Boron-based organic synthesis through reactivity control by substituents on boron." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136275.
Full text
31
Schwerdtfeger, Ulrich. "Borna-Enzephalitis und Mikroglia : immunhistochemische und photometrische Untersuchungen /." Hamburg : Kovač, 1996. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=007166537&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
Full text
32
Vergnaud, J. "Ligands ambiphiles pyridine/borane et phosphine /borane : Synthèse, Structure, Coordination et Réactivité." Phd thesis, Université Paul Sabatier - Toulouse III, 2007. http://tel.archives-ouvertes.fr/tel-00273327.
Full textAbstract:
Cette thèse traite de l'utilisation de molécules dîtes ambiphiles, comportant à la fois un site donneur et accepteur d'électrons, en chimie organométallique, en tant que ligand.Dans le premier chapitre, une étude bibliographique décrit l'utilisation des acides de Lewis du groupe 13 en tant que co-catalyseur en chimie organométallique, afin de mieux comprendre quel rôle pourrait jouer celui-ci au sein d'un ligand ambiphile coordiné sur un métal de transition. Les différents modes de coordination de ces ligands sont examinés. Les rares contributions traitant de la réactivité de ce type de complexes sont également décrites.
Le second chapitre décrit la synthèse par couplage bore-carbone d'une nouvelle famille de ligands ambiphiles, 2-picolylboranes. En fonction des substituants du bore, ces composés sont obtenus sous forme dimère ou monomère fermé par interactions datives donneur-accepteur, inter ou intramoléculaires. Le comportement en solution du 2-picolylBCy2 a été examiné attentivement. Un équilibre entre la forme dimère et monomère est mis en évidence. Des calculs théoriques valident nos conclusions. La coordination de ce ligand sur plusieurs précurseurs métalliques est étudiée. Un exemple rare de coordination pontante donneur→Ru-Cl→accepteur a été caractérisé dans le complexe [(p-cym)RuCl2(2-picolylBCy2)].
Dans le troisième chapitre, la synthèse par hydroboration d'une famille de ligands ambiphiles, 1,2-phosphinoethylborane, est décrite. Deux complexes de ruthénium neutres contenant ces ligands, ainsi que leur dérivés cationiques sont caractérisés. Des tests catalytiques préliminaires d'hydrosilylation du benzaldéhyde avec l'un des complexes cationiques ont montré la dégradation rapide du pré-catalyseur en un complexe ruthénacycle original. Sa réactivité avec un chloroborane et un chloroalane est étudiée.
33
Cui, Jian. "Synthesis and characterization of new boron-nitrogen and boron-nitrogen-phosphorus systems." [Fort Worth, Tex.] : Texas Christian University, 2009. http://etd.tcu.edu/etdfiles/available/etd-03162010-123538/unrestricted/Cui.pdf.
Full text
34
Ceberg, Crister. "Pharmacokinetics and biodistribution of boron compounds foundations for boron neutron capture theory /." Lund : Dept. of Radiation Physics, Lund University, 1994. http://books.google.com/books?id=wnhrAAAAMAAJ.
Full text
35
Castro, Susana Patricia. "Characterization of the boron doping process using boron nitride solid source diffusion." Raleigh, NC : North Carolina State University, 1999. http://www.lib.ncsu.edu/etd/public/etd-2923142349901421/etd.pdf.
Full text
36
Chung, Yoonsun. "Radiobiological evaluation of new boron delivery agents for boron neutron capture therapy." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44784.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.Includes bibliographical references (p. 123-132).
This thesis evaluates the radiobiological effectiveness of three new boron compounds namely a boronated porphyrin (BOPP) and two liposome formulations for neutron capture therapy (BNCT). The methodology utilizes in vitro and in vivo comparisons that characterize compounds relative to boric acid and boronophenylalanine (BPA). In vitro evaluations utilized a colorimetric assay and 96-well plates to minimize the quantities of compound required for testing. The assay was optimized for the murine SCCVII, squamous cell carcinoma to determine the chemical toxicity and relative cellular uptake of a compound. BOPP was toxic at low concentrations and comparisons between the different compounds for thermal neutron irradiations were performed with approximately 5 [mu]g 10B/ml in the culture medium to allow radiation induced effects to govern the observed response. Using less than 300 [mu]g of compound and 250 kVp X-rays as control irradiations, a compound biological effectiveness (CBE) of 3.3 ± 0.7 was determined for BOPP that is comparable to the result for boric acid (3.5 ± 0.5) indicating a non-selective intracellular accumulation of 10B. BPA has a significantly higher CBE of 6.1 + 0.7. Boronated liposomes (MAC-16 and MAC+TAC) were evaluated with the EMT-6 murine mammary carcinoma. Biodistribution studies showed high 10B uptake in tumor (20-40 [mu]g 10B/g) 30 hours after a single i.v. injection (dose 6-20 [mu]g 10B per gram of body weight). Tumor control experiments were performed using thermal neutrons to study the efficacy of the boron delivered by liposomes and BPA. The MAC-16 produced a 16 % tumor control and BPA (dose 43 [mu]g 10B/gbw) 63 % for tumor boron concentrations of approximately 20 [mu]g 10B/g and the same neutron fluence.
(cont.) Liposome doses were limited by injection volume and so two injections were tried 2-hours apart that doubled the boron concentration in tumor compared to a single administration. This improved the therapeutic response to 67 % with less apparent skin damage than with BPA. Microscopic studies using fluorescent labeled liposomes revealed 10B was nonuniformly distributed and concentrated at the edge of the tumor. Based on these studies in the tumor cell lines chosen neither of the compounds appear superior to BPA.
by Yoonsun Chung.
Ph.D.
37
Vergnaud, Jérôme. "Ligands ambiphiles pyridine/borane et phosphine/borane : synthèse, structure, coordination et réactivité." Toulouse 3, 2007. http://thesesups.ups-tlse.fr/67/.
Full textAbstract:
Cette thèse traite de l'utilisation de molécules dîtes ambiphiles, comportant à la fois un site donneur et accepteur d'électrons, en chimie organométallique, en tant que ligand. Dans le premier chapitre, une étude bibliographique décrit l'utilisation des acides de Lewis du groupe 13 en tant que co-catalyseur en chimie organométallique, afin de mieux comprendre quel rôle pourrait jouer celui-ci au sein d'un ligand ambiphile coordiné sur un métal de transition. Les différents modes de coordination de ces ligands sont examinés. Les rares contributions traitant de la réactivité de ce type de complexes sont également décrites. Le second chapitre décrit la synthèse par couplage bore-carbone d'une nouvelle famille de ligands ambiphiles, 2-picolylboranes. En fonction des substituants du bore, ces composés sont obtenus sous forme dimère ou monomère fermé par interactions datives donneur-accepteur, inter ou intramoléculaires. Le comportement en solution du 2-picolylBCy2 a été examiné attentivement. Un équilibre entre la forme dimère et monomère est mis en évidence. Des calculs théoriques valident nos conclusions. La coordination de ce ligand sur plusieurs précurseurs métalliques est étudiée. Un exemple rare de coordination pontante donneur->Ru-Cl->accepteur a été caractérisé dans le complexe [(p-cym)RuCl2(2-picolylBCy2)]. Dans le troisième chapitre, la synthèse par hydroboration d'une famille de ligands ambiphiles, 1,2-phosphinoethylborane, est décrite. Deux complexes de ruthénium neutres contenant ces ligands, ainsi que leur dérivés cationiques sont caractérisés. Des tests catalytiques préliminaires d'hydrosilylation du benzaldéhyde avec l'un des complexes cationiques ont montré la dégradation rapide du pré-catalyseur en un complexe ruthénacycle original. Sa réactivité avec un chloroborane et un chloroalane est étudiéeThe present contribution deals with the use of ambiphilic molecules featuring both a Lewis base and a Lewis acid site, as ligands in organometallic chemistry. In the first chapter, a bibliographic study describes the behaviour of Lewis acids of group 13 in organometallic chemistry. Their role as co-catalysts is examined in order to better understand how the Lewis acid could behave in a complex featuring an ambiphilic ligand. The different coordination modes of those ligands are reviewed. The rare contributions dealing with the reactivity of those complexes are also examined. The second chapter describes the synthesis by carbon-boron coupling of a new family of ambiphilic ligands, namely 2-picolylboranes. Depending on the borane substituents, they are obtained as dimer or closed monomer via inter or intramolecular donor-acceptor dative interaction. The behaviour of 2-picolylBCy2 in solution is examined in details by NMR. An equilibrium between a dimer and a closed monomer form is evidenced. Theoretical calculations ascertain our conclusions. Coordination of this ligand to several transition metal precursors is studied. .
38
Andrae, Daniel, and Elvira Pertermann. "Mediothek Borna – ein Pilotprojekt." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-85097.
Full textAbstract:
Der effektivste Einsatz der zur Verfügung stehenden finanziellen und personellen Ressourcen für Bibliotheksarbeit steht vielerorts immer wieder auf der Tagesordnung. So auch bereits Ende der neunziger Jahre im damaligen Landkreis Leipziger Land.
39
Cho, Namtae. "Processing of Boron Carbide." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11567.
Full textAbstract:
The processing of boron carbide powder including sintering optimization, green body optimization and sintering behavior of nano-sized boron carbide was investigated for the development of complex shaped body armor.
Pressureless sintered B4C relative densities as high as 96.7% were obtained by optimizing the soak temperature, and holding at that temperature for the minimum time required to reach terminal density. Although the relative densities of pressureless sintered specimens were lower than that of commercially produced hot-pressed B4C, their (Vickers) hardness values were comparable. For 4.45cm diameter and 1.35cm height disk shaped specimens, pressureless sintered to at least 93.0% relative density, post-hot isostatic pressing resulted in vast increases in relative densities (e.g. 100.0%) and hardness values significantly greater than that of commercially produced hot-pressed B4C.
The densification behavior of 20-40nm graphite-coated B4C nano-particles was studied using dilatometry, x-ray diffraction and electron microscopy. The higher than expected sintering onset from a nano-scale powder (15008C) was caused by remnant B2O3 not removed by methanol washing, keeping particles separated until volatilization and the carbon coatings, which imposed particle to particle contact of a substance more refractory than B4C. Solid state sintering (1500-18508C) was followed by an arrest in contraction attributed to formation of eutectic liquid droplets of size more than 10X the original nano-particles. These droplets, induced to form well below known B4C-graphite eutectic temperatures by the high surface energy of nano-particles, are interpreted to have quickly solidified to form a vast number of voids in particle packing, which in turn, impeded continued solid state sintering. Starting at 22008C, a permanent liquid phase formed which facilitated a rapid measured contraction by liquid phase sintering and/or compact slumping.
40
Ozkol, Engin. "Production Of Boron Nitride." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609646/index.pdf.
Full textAbstract:
Boron nitride is found mainly in two crystal structuresin hexagonal structure (h-BN) which is very much like graphite and in cubic structure (c-BN) with properties very close to those of diamond. h-BN is a natural lubricant due to its layered structure. It is generally used in sliding parts of the moving elements such as rotating element beds in turbine shafts. Since c-BN is the hardest known material after diamond it is used in making hard metal covers. In addition to its possible microelectronics applications (can be used to make p-n junction), its resistance to high temperatures and its high forbidden energy gap are its superiorities over diamond. Recent studies have shown that c-BN can be produced by Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) in plasma. But these studies have failed to determine how all of the production parameters (boron and nitrogen sources, composition of the gas used, substrate, RF power, bias voltage, substrate temperature) affect the c-BN content, mechanical stress and the deposition rate of the product with a systematic approach. The systematic study was realized in the range of available experimental ability of the present PVD and CVD equipment and accessories. The BN films were produced in the plasma equipment for CVD using RF and MW and magnetron sputtering and were studied with the measurement and testing facilities. It is believed that with this approach it will be possible to collect enough experimental data to optimize production conditions of BN with desired mechanical and optoelectronic properties. h-BN films were successfully deposited in both systems. It was possible to deposit c-BN films with the MW power, however they were weak in cubic content. Deposition at low pressures eliminated the hydrogen contamination of the films. High substrate temperatures led to more chemically and mechanically stable films.
41
Lee, Hyukjae. "Sintering of boron carbide." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19631.
Full text
42
Smil, David V. "Boron tethered radical cyclizations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0006/MQ40735.pdf.
Full text
43
Keep, Ann Kathleen. "Ruthenium boron cluster chemistry." Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/272941.
Full text
44
Queval, Pierre. "Phosphures borane de lithium." Caen, 2011. http://www.theses.fr/2011CAEN2053.
Full textAbstract:
Les phosphures borane de lithium sont des espèces obtenues par déprotonation de phosphines borane secondaires par une base de type alkyllithien. L’analyse de ces composés, dont la structure est peu connue, par spectroscopie de résonance magnétique nucléaire multinoyaux a mis en évidence des interactions entre les atomes de lithium et d’hydrogènes du groupement borane et l’absence d’interaction PLi. En accord avec la structure de ces composés, une réactivité duale de P-nucléophile et de réducteur a été mise en évidence par réaction avec des dérivés carbonylés. L’issue de la réaction dépend des conditions imposées à la réaction : cinétique (produit de P-addition) ou thermodynamique (produit de réduction). Le processus de réduction a également conduit à des oligomères linéaires de phosphines borane. Dans une seconde partie, la synthèse de phosphines borane P-énantioenrichies a été effectuée par dédoublement dynamique thermodynamique de phosphures borane encombrés en présence d’amines énantiopures dérivées de 3-aminopyrrolidines, offrant pour la première fois un accès aux dérivés de configuration (S). Les phosphures borane de lithium sont des espèces obtenues par déprotonation de phosphines borane secondaires par une base de type alkyllithien. L’analyse de ces composés, dont la structure est peu connue, par spectroscopie de résonance magnétique nucléaire multinoyaux a mis en évidence des interactions entre les atomes de lithium et d’hydrogènes du groupement borane et l’absence d’interaction PLi. En accord avec la structure de ces composés, une réactivité duale de P-nucléophile et de réducteur a été mise en évidence par réaction avec des dérivés carbonylés. L’issue de la réaction dépend des conditions imposées à la réaction : cinétique (produit de P-addition) ou thermodynamique (produit de réduction). Le processus de réduction a également conduit à des oligomères linéaires de phosphines borane. Dans une seconde partie, la synthèse de phosphines borane P-énantioenrichies a été effectuée par dédoublement dynamique thermodynamique de phosphures borane encombrés en présence d’amines énantiopures dérivées de 3-aminopyrrolidines, offrant pour la première fois un accès aux dérivés de configuration (S)Lithium phosphido-boranes are anionic species prepared by deprotonation of secondary phosphane-boranes using an organolithium base. Multinuclear NMR analysis of these poorly studied compounds evidenced lithium-hydrides interactions and absence of lithium-phosphorus one. According to their structure, these compounds develop a dual reactivity behaving as both P-nucleophile and reducing agent using carbonyl compounds as substrates. The issue of the reaction depends on the kinetic or thermodynamic control imposed to the reaction medium: P-addition or reduction, respectively. Linear polyphosphinoboranes have also been formed during the reduction process. In a second part, P-enantioenriched phosphane-boranes have been synthesized starting form sterically hindered phosphane-boranes using enantiopure amines derived from 3-aminopyrrolidine as chiral agents. This approach, involving a thermodynamic dynamic resolution process, leads for the first time to tertiary P-stereogenic phosphane-boranes, having the (S)-configuration
45
Bin, Darwish Nawaf Naif. "Boron removal from saline water." Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa42237.
Full textAbstract:
Although boron is an essential micronutrient for some plants, animals and humans, the range between deficiency and excess is narrow. The effects of excess boron on plants includes the reduction of root cell division, retarded shoot and root growth, inhibition of photosynthesis, deposition of lignin and suberin and decrease in leaf chlorophyll. A report by the World Health Organization (WHO) suggests a safe maximum level of boron daily intake of 13 mg/d an excessive level of boron can be toxic to and can causes serious diseases. There are several methods applied for boron removal from aqueous solutions and seawater. Among these methods, ion exchange, which is the most extensively method. Ion-exchange and adsorption are widely used techniques to remove metals and other solutes from aqueous solutions. This includes the removal of boron from reverse osmosis (RO) permeate in the process of seawater desalination. The use of boron-selective ion exchange resins based on macroporous polystyrene matrices with the active group N-methyl-D-glucamine (NMG) seems to still have the highest importance for the elimination of boron. Kinetics of adsorption or IEX is in many cases strongly influenced by diffusion resistance in particles of adsorbent. This resistance can be decreased by using smaller particles. Sorbents can be used as very fine particles which results in increase of the surface area and the process rate, considerably. Hybrid adsorption membrane filtration has gained the interest lately as it can be used for the removal of very small quantities of harmful substances from water. This thesis deals used hybrid system on both lab and pilot scale where a pilot plant was designed for the removal of boron. Boron separation combines two phenomena: i) sorption with fine sorbent particles and ii) membrane separation of B-loaded macromolecules/particles. The hybrid system includes two separation loops. Loop 1: Binding of boron (B) on Amberlite IRA743 resin (S), which is subsequently followed by separation of this (BS) complex from the water by means of semi-permeable microfiltration membrane. Here, pure water (W) is the main product whereas the complex (BS) passes to the second stage of separation. The effects of different parameters on boron removal using Amberlite IRA743 resin were investigated in this thesis. These parameters are, resin particle size, solution pH, temperature, contact time, initial boron concentration, resin concentration and the existence of different salts and ions like NaCl, Na2SO4 and MgCl2. The removal increased with increasing pH, temperature, contact time and resin dosage while it decreased with increasing initial boron concentration and resin particle size. For the microfiltration stage, three Polyvinylidene fluoride (PVDF) with different pore size have been used in this thesis. The effects of operational parameters like membrane pore size, transmembrane pressure, resin concentration and pH on permeate flux for hybrid adsorption-microfiltration were studied. The permeate flux increased with increasing the transmembrane pressure and pH but it decreased with increasing the resin concentration. The regeneration of loaded resin with boron was investigated. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) at different concentrations have been used for the elution of boron from the saturated resin and then washing with sodium hydroxide (NaOH). There was an improvement in the boron removal after cycles of regeneration. The integrated adsorption-microfiltration was applied for boron removal from water and encouraging results were achieved.
46
Wolsey, Dawn-Marie. "Born again architecture." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ39711.pdf.
Full text
47
Khalaf, Tania Levin C. Melinda. "Born in Beirut." [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-3954.
Full text
48
Hilton-Hagemann, Brandi L. "Natural born enemies?" Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1594498531&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
Full text
49
Todd, Graham. "Born Under Punches." Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1490874484128209.
Full text
50
Khalaf, Tania. "Born in Beirut." Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc3954/.
Full textAbstract:
The film starts with another ordinary day, two elderly men playing Backgammon, cars passing by, children playing in the street; scenes anyone anywhere in the world can relate to. Seemingly without warning, as the sun set on that ordinary day, the audience is taken on a perilous journey through war-torn Beirut. Born in Beirut is a thoughtful and poetic examination of war through the eyes of a child who lived through endless conflict in war-torn Beirut. The film examines the futility of war and the price paid in innocent lives.