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T Bak

Publications and source records attributed to T Bak.

At least 19 recordsLinked to original sources
PubMed2006

Electrical properties of niobium-doped titanium dioxide. 1. Defect disorder.

The present work reports the electrical conductivity and thermoelectric power for Nb-doped TiO(2) at elevated temperatures (1073-1298 K) in the gas phase of controlled oxygen activity, 10(-14) Pa < p(O(2)) < 75 kPa. It is shown that in reduced conditions the Nb-doped TiO(2) exhibits metallic-type conductivity. This finding paves the way for the development of high-performance photoelectrodes with substantially reduced internal energy losses during charge transport. The present work also determined the equilibrium constant for the formation of oxygen vacancies and titanium vacancies for Nb-doped TiO(2).

Journal Article↗
PubMed2006

Electrical properties of niobium-doped titanium dioxide. 2. Equilibration kinetics.

The present work reports isothermal gas/solid equilibration kinetics for Nb-doped TiO(2) (0.65 atom %) at elevated temperatures (1073-1298 K) within narrow ranges of oxygen activity spanning between 10(-13) Pa and 75 kPa. The equilibration kinetics were monitored using electrical conductivity measurements. The kinetic data were used to determine the chemical diffusion coefficient (D(chem)). D(chem) as a function of p(O(2)) exhibits a complex dependence, which is considered in terms of defect disorder and the related concentrations of electronic charge carriers. The activation energy of D(chem) in the p(O(2)) range 10 Pa < p(O(2)) < 75 kPa varies in the range 88.0-98.2 kJ/mol. It is important to note that the chemical diffusion coefficient in strongly reduced conditions [p(O(2)) = 10(-9) Pa] exhibits a negative temperature dependence of D(chem) (-67.2 kJ/mol). This finding indicates that under these conditions transport in a chemical potential gradient is consistent with metallic charge transport.

Journal Article↗
PubMed2006

Defect disorder of titanium dioxide.

The present work derived defect disorder diagram representing the effect of oxygen activity on the concentration of both ionic and electronic defects for undoped TiO2. This diagram was determined using the equilibrium constants derived in the present work, including (i) the intrinsic electronic equilibrium constant, (ii) the equilibrium constant for the formation of oxygen vacancies, and (iii) equilibrium constant for the formation of titanium vacancies. These equilibrium constants are consistent with three properties determined independently, including: electrical conductivity, thermoelectric power and change of mass determined by thermogravimetry. The derived defect disorder diagram may be used for tailoring semiconducting properties of TiO2 that are desired for specific applications through the selection of optimized processing conditions.

Journal Article↗
PubMed2006

TiO2 surface active sites for water splitting.

The mechanism of photoreactivity between the TiO(2) surface and H(2)O, and the related charge transfer, is considered in terms of both collective and local properties. It is shown that the effective charge transfer between TiO(2) and water requires the presence of surface active sites that are able to provide electron holes to adsorbed water molecules. Titanium vacancies located at or near the surface are identified as the active sites for water adsorption leading to the formation of an active complex and resulting, in consequence, in water splitting. A model of the photoreactivity between the TiO(2) surface and water is proposed. This model indicates that the photoreactivity of the TiO(2)-based photoelectrode may be enhanced through imposition of the surface active sites (Ti vacancies) in a controlled manner by surface engineering.

Journal Article↗
PubMed2006

Electrical properties and defect chemistry of TiO2 single crystal. I. Electrical conductivity.

The present work reports the electrical properties of high-purity single-crystal TiO(2) from measurements of the electrical conductivity in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities in the range 10(-13) to 10(5) Pa. The effect of the oxygen activity on the electrical conductivity indicates that oxygen vacancies are the predominant defects in the studied ranges of temperature and oxygen activities. The electronic and ionic lattice charge compensations were revealed at low and high oxygen activities, respectively. The determined semiconducting quantities include: the activation energy of the electrical conductivity (E(sigma) = 125-205 kJ.mol(-1)), the activation energies of the electrical conductivity components associated with electrons (E(n) = 218 kJ.mol(-1)), electron holes (E(p) = 34 kJ.mol(-1)), and ions (E(i) = 227 kJ.mol(-1)), and the enthalpy of motion for electronic defects (DeltaH(m) = 4 kJ/mol). The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. The obtained data allow the determination of the n-p demarcation line in terms of temperature and oxygen activities. The band gap determined from the electronic component of the electrical conductivity is 3.1 eV.

Crystallization↗
PubMed2006

Electrical properties and defect chemistry of TiO2 single crystal. II. Thermoelectric power.

The present work reports the thermoelectric power of high-purity single-crystal TiO(2) in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities, p(O(2)), in the range 10(-13) to 7.5 x 10(4) Pa. The thermoelectric power versus log p(O(2)) dependence for strongly reduced TiO(2) at p(O(2)) < 10(-5) Pa may be approximated by a slope of 1/6, which is consistent with the defect disorder governed by electronic charge compensation of oxygen vacancies. The thermoelectric power data confirm that oxygen vacancies are the predominant ionic defects. These data indicate that TiO(2) at high p(O(2)) exhibits p-type properties. It is shown that the p(O(2)) related to the n-p transition increases with increase of temperature.

Journal Article↗
PubMed2006

Electrical properties and defect chemistry of TiO2 single crystal. III. Equilibration kinetics and chemical diffusion.

The equilibration kinetics of high-purity single-crystal TiO(2) were monitored using measurements of electrical conductivity in the temperature range 1073-1323 K and oxygen activity, p(O(2)), range 10(-13) to 75 kPa. The kinetics data were used to determine the chemical diffusion coefficient (D(chem)) within narrow ranges of p(O(2)). There was observed a complex effect of the p(O(2)) on the D(chem), which exhibits a maximum at the n-p transition. The effect of the p(O(2)) on the D(chem) was discussed in terms of the defect disorder and the related semiconducting properties. The activation energy of the D(chem), which also varies with the p(O(2)), exhibits a maximum at p(O(2)) = approximately 10(4) Pa (143 kJ/mol).

Journal Article↗
PubMed2006

Electrical properties and defect chemistry of TiO2 single crystal. IV. Prolonged oxidation kinetics and chemical diffusion.

Measurements of both electrical conductivity and thermoelectric power were used to monitor the equilibration kinetics of undoped single-crystal TiO(2) during prolonged oxidation at 1123 and 1323 K and p(O(2)) = 75 kPa. Two kinetics regimes were revealed: kinetics regime I (rapid kinetics), which is rate-controlled by the transport of oxygen vacancies, and kinetics regime II (slow kinetics), which is rate-controlled by the transport of titanium vacancies. The incorporation of titanium vacancies allows undoped p-type TiO(2) to be processed in a controlled manner. The kinetics data were used to determine the chemical diffusion coefficient (D(chem)) associated with the transport of titanium vacancies, which is equal to D(chem) = 8.9 x 10(-14) m(2) s(-1) and D(chem) = 9.3 x 10(-15) m(2) s(-1) at 1323 and 1123 K, respectively.

Journal Article↗
PubMed2006

Outcomes of donor evaluations for adult-to-adult right hepatic lobe living donor liver transplantation.

The purpose of this study is to determine the role of liver biopsy and outcome of patients undergoing donor evaluation for adult-to-adult right hepatic lobe living donor liver transplantation (LDLT). Records of patients presenting for a comprehensive donor evaluation between 1997 and February 2005 were reviewed. Liver biopsy was performed only in patients with risk factors for abnormal histology. Two hundred and sixty patients underwent a comprehensive donor evaluation and 116 of 260 (45%) were suitable for donation, 14 of 260 (5.4%) did not complete evaluation and 130 of 260 (50%) were rejected. Four patients underwent unsuccessful hepatectomy surgery due to discovery of intraoperative abnormalities. Between 1997 and 2001, the acceptance rate of donor candidates (63%) was higher than 2002-2005 (36%), p < 0.0001. Sixty-six of the 150 eligible patients (44%) fulfilled criteria for liver biopsy and 28 of 66 (42%) had an abnormal finding. Less than half of the patients undergoing donor evaluation were suitable donors and the donor acceptance rate has declined over time. A large proportion of the patients undergoing liver biopsy have abnormal findings. Our evaluation process failed to identify 4 of 103 who had aborted donor surgeries.

Adolescent↗
PubMed2005

Conversion of stable liver transplant recipients from a twice-daily Prograf-based regimen to a once-daily modified release tacrolimus-based regimen.

INTRODUCTION: Modified release (MR) tacrolimus is an extended release formulation administered once daily. The purpose of this pharmacokinetic (PK) study was to evaluate tacrolimus exposure in stable liver transplant recipients converted from Prograf twice a day to MR tacrolimus once daily. METHODS: This was an open-label, multicenter study with a single sequence, four-period crossover design. Eligible patients were 18 to 65 years of age, >6 months posttransplant with stable renal and hepatic function and receiving stable doses of Prograf twice a day for >2 weeks prior to enrollment. Patients received Prograf twice a day on days 1 to 14 and 29 to 42. Patients were converted to the same milligram-for-milligram daily dose of MR once daily on days 15 to 28 and 43 to 56. Twenty-four-hour PK profiles were obtained on days 14, 28, 42, and 56. Laboratory and safety parameters were also evaluated. RESULTS: Of 70 patients, 62 completed all four PK profiles. The AUC0-24 of tacrolimus was comparable for Prograf twice a day (days 14 and 42) and MR tacrolimus once daily (days 28 and 56). The 90% confidence intervals for MR tacrolimus versus Prograf at steady state (days 28 and 56 vs days 14 and 42) was 0.85 to 0.92 for AUC0-24. MR tacrolimus was well tolerated with a safety profile comparable to that of Prograf. AUC0-24 was highly correlated to Cmin for Prograf (day 14, r = .93; Day 42, r = .89) and for MR tacrolimus (day 28, r = .93; day 56, r = .92). Renal and liver function remained stable. One patient experienced acute rejection. CONCLUSION: The steady-state tacrolimus exposure of MR tacrolimus once daily is equivalent to Prograf twice a day after a milligram-for-milligram conversion in stable liver transplant recipients.

Area Under Curve↗
PubMed2004

Relationships between the turnover before slaughter, welfare and the occurrence of defective DFD type meat in cattle.

In this article we have presented genetic predispositions and the influence of numerous factors that occur during cattle fattening, transport and holding in slaughter plants, on their welfare and subsequently on the occurrence of defective meat, known in the literature as DFD (Dark, Firm, Dry) meat. Such meat is unwillingly bought by contemporary consumers because of its consistency and processing plants cannot intend it for production of durable processed meat due to its compliance to decay. To a great extent the occurrence of this meat defect is caused by people as a result of ignorance and incompliance of cattle welfare. It should also be remarked that there is a rising number of consumers interested in the place of origin of cattle and the way it was treated.

Abattoirs↗
PubMed2002

The most important causes for quantitative and qualitative losses during breeding and turnover before slaughtering of farm animals.

The present review article deals with the current knowledge on the most important reasons of quantitative and qualitative losses during breeding and turnover before slaughtering of farm animals. At present, the profitability of every economic activity of people is an indispensable necessity. As regards farm animals there are many factors, seemingly banal ones, that determine the final economical effect and satisfaction of such activity. Many essential errors are made by producers as a result of ignorance or not complying with the basic needs of their behaviour. The turnover only deepens these neglects. The most essential limitations of these quantitative and qualitative losses are the proper selection and joining of the animals as well as an exact knowledge and complying with their natural behaviour. Such activity decreases animal stress, improves a proper welfare and consequently increases economical effects considerably.

Abattoirs↗
PubMed2001

Psychiatric symptoms and CAG repeats in neurologically asymptomatic Huntington's disease gene carriers.

The putative relationship between the psychiatric profile of a sample of neurologically asymptomatic Huntington's disease gene carriers and CAG repeats was investigated. The psychiatric assessments (by consultant psychiatrist and computerised battery) were undertaken before the genetic testing was carried out. In this way, the informational distortions caused by neurological and cognitive deficits were avoided. The hypothesis that there is a relationship between psychiatric and CAG repeats was tested by seeking direct correlations between psychiatric systems and CAG repeats, and also by correcting the correlation by the number of years above or below the estimated age of onset in Huntington's disease. Scores for irritability and cognitive failures were high in the sample. There was no correlation between any psychiatric variable and CAG repeats. Possible explanations for this lack of correlations are discussed.

Adenine↗
PubMed2001

Liver transplantation using sirolimus and minimal corticosteroids (3-day taper).

At our center, we have performed liver transplantation since 1995 with a rapid-taper steroid protocol (weaning steroids by day 14 posttransplantation). Beginning in 2000, we further reduced the use of corticosteroids to 3 days and added sirolimus to our immunosuppressive regimen. We report our experience with 39 patients who underwent liver transplantation with either tacrolimus or cyclosporin A (Neoral; Novartis Pharmaceuticals Corp., Summit, NJ) and sirolimus, with a 3-day tapered dose of corticosteroids. Thirty-two patients received a cadaveric graft and 7 patients received a right hepatic lobe from a living donor. All patients initially were administered either tacrolimus (0.1 mg/kg/d) or cyclosporin A (10 mg/kg/d) and sirolimus (6 mg/d for 1 day, followed by 2 mg/d), in addition to methylprednisolone on the first 3 days (1, 0.5, and 0.5 g/d) after transplantation. Patients were administered corticosteroids for presumptive or biopsy-proven evidence of acute cellular rejection (methylprednisolone, 1, 0.5, and 0.5 g on 3 successive days). Seventeen patients were administered tacrolimus and 22 patients were administered cyclosporin A. Six patients were excluded from analysis because they were administered sirolimus for less than 2 weeks. Mean duration of follow-up was 124 days. Patient survival was 36 of 39 patients (92%), and graft survival was 35 of 39 grafts (89%). Ten of 33 patients (30%) experienced 12 episodes of rejection (7 biopsy proven, 5 presumptive) compared with 70% in historical controls (P <.01). OKT3 was required in 1 of 33 patients (3%) compared with 37% in controls (P <.01). Twenty-six of 33 patients (79%) were not administered prednisone, and 7 of 33 patients (21%) were administered prednisone for reasons other than rejection. Posttransplantation, there was no significant change in values for creatinine, glucose, aspartate aminotransferase, bilirubin, cholesterol, and white blood cell counts. Platelet counts were significantly reduced, and hematocrits were significantly elevated (P <.05). Liver transplantation may be successfully performed with minimal use of corticosteroids by using sirolimus and either tacrolimus or cyclosporin A. Despite the absence of prednisone from our immunosuppressive protocol, the incidence of rejection and OKT3 use was lower than in historical controls. Patient and graft survival rates were identical to those of historical controls. The findings in this report will serve as the basis for a formal trial evaluating the efficacy of sirolimus in liver transplantation.

Cyclosporine↗
PubMed2001

Dyslipidemia during sirolimus therapy in liver transplant recipients occurs with concomitant cyclosporine but not tacrolimus.

Since its approval as an immunosuppressive agent in renal transplantation, sirolimus (RAPA) recently has been used in the primary immunosuppression regimen at several liver transplant centers. One of the major side effects of RAPA is hypercholesterolemia, which is reported in up to 44% of patients. We describe our experience in 57 primary liver transplant recipients treated with RAPA and either cyclosporine A (CSA) or tacrolimus (TAC). We report the incidence and severity of hypercholesterolemia using a prednisone-free immunosuppressive regimen. Between January 2000 and September 2000, a total of 57 patients underwent transplantation at the University of Colorado Health Sciences Center (Denver, CO) with RAPA and either CSA or TAC. The initial 10 patients who underwent transplantation under this protocol were not administered corticosteroids, and the subsequent 47 patients were administered only 3 doses of methylprednisolone days 0, 1, and 2 postoperatively (1, 0.5, and 0.5 g, respectively). Total fasting cholesterol, high-density cholesterol, low-density cholesterol, and triglyceride levels were measured at monthly intervals. Mean serum cholesterol level was significantly greater in CSA patients (200 mg/dL) compared with TAC patients (158 mg/dL; P =.0003). Serum triglyceride levels were more than 2-fold greater with CSA (292 mg/dL) compared with TAC (134 mg/dL; P =.002). Hypercholesterolemia (cholesterol > 240 mg/dL) was present in 10 of 57 patients (18%) and was significantly more common in CSA-treated patients (8 of 27 patients; 30%) compared with TAC-treated patients (2 of 30 patients; 6%; P <.05). Hypertriglyceridemia (serum triglyceride > 300 mg/dL) was present in 10 of 57 patients (18%) and was significantly more common in CSA-treated patients (9 of 27 patients; 33%) compared with TAC-treated patients (1 of 30 patients; 3%; P <.05). We conclude that (1) concomitant use of TAC with RAPA reduces the prevalence and severity of posttransplantation dyslipidemia, and (2) these findings have important implications in the prevention of complications of hypercholesterolemia in liver transplant recipients.

Adult↗
PubMed2001

Right hepatic lobe donation for living donor liver transplantation: impact on donor quality of life.

Adult right hepatic lobe living donor liver transplantation (LDLT) has rapidly gained widespread acceptance as an effective procedure for selected patients with end-stage liver disease. However, there are currently no published data on the effect of this procedure on the quality of life of donors. We report the results of a survey of our living liver transplant donors to determine the effect of right hepatic lobe donation on quality of life. We have performed 30 LDLTs since 1997; 24 of these have a follow-up of 4 months or longer. In August 2000, these patients were sent a questionnaire (including a Medical Outcomes Study 36-Item Short-Form Survey) regarding psychosocial outcomes and symptoms after surgery. Major complications occurred in 4 of 24 patients (16%), and minor complications, in 4 of 24 patients (16%). Complete recovery occurred in 75% of patients at a mean time of 3.4 months. Ninety-six percent of patients returned to the same predonation job after a mean time of 2.4 months, and 66% of patients required a period of light-duty work for a mean of 2.8 months before returning to full-duty work. A change in body image was reported in 42% of patients, and 71% reported mild ongoing symptoms (primarily abdominal discomfort) that they related to the donor surgery for which 29% sought evaluation by a physician. The donor's relationship with the recipient was the same or better in 96% of donors, and the relationship with the donor's significant other was the same or better in 88% of donors. Mean out-of-pocket expenses incurred by donors were $3,660. Sixty-three percent of donors reported experiencing more pain than anticipated. All patients would donate again if necessary, and 96% benefited from the donor experience. In conclusion, (1) all our donors are alive and well after donation; (2) almost all donors were able to return to predonation employment status within a few months; (3) most donors have mild persistent abdominal symptoms, and some donors had a change in body image that they attribute to the donor surgery; and (4) this information should be provided to potential donors so they may better understand the impact of donor surgery.

Adult↗
PubMed2001

Adult-to-adult living donor liver transplantation using right-lobe grafts: results and lessons learned from a single-center experience.

Living donor liver transplantation (LDLT) for adults is now a practical alternative to cadaveric liver transplantation. Use of right-lobe grafts has become the preferred donor procedure. Because of the complexity of this operation, a learning curve is to be expected. We report the outcome of our first 41 LDLTs at the University of Colorado Health Sciences Center (Denver, CO). We also discuss the lessons learned and the resultant modifications in the procedure that evolved during our series. Patient records were retrospectively reviewed between August 1997 and February 2001 for the following end points: recipient survival, graft survival, and donor and recipient complications. Thirty-eight of 41 living donor liver transplant recipients (93%) are alive and well postoperatively with a mean follow-up of 9.6 months. Four patients required retransplantation secondary to technical problems (9.8%); all 4 patients were in our initial 11 cases. Modification of the donor liver plane of transection resulted in venous outflow improvement. Also, biliary management was modified during the series. Donor complications are listed; all 41 donors have returned to normal pretransplantation activity. Our results indicate that LDLT can be performed safely with excellent donor and recipient outcomes. Dissemination of our experience can help shorten the learning curve for other institutions.

Adult↗