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Papers by Lubomir Nikolov

Research paper thumbnail of Nonlinear chi(2) and chi(3) spectroscopy of magnesium sulfite hexahydrate single crystal

The second- and third-order nonlinear optical properties of Magnesium Sulfite Hexahydrate (MgSO 3... more The second- and third-order nonlinear optical properties of Magnesium Sulfite Hexahydrate (MgSO 3.6H IIO) were studied by Second-Harmonic Generation (SHG) and Degenerate Four-Wave Mixing (DFWM). Nanosecond pumping by Nd:YAG laser having a variable reflection output coupler was used. The effective quadratic (χ (2)) and cubic (χ (3)) nonlinear susceptibility values are obtained at room temperature. The dispersion of the nonlinear optical susceptibility of MgSO 3.6H IIO is also discussed.

Research paper thumbnail of Herbizidwirkung einiger Thioharnstoffderivate

Archives of Phytopathology and Plant Protection, 1972

Research paper thumbnail of Evaluation of clinical and socio-demographic risk factors for antibacterial resistance of Helicobacter pylori in Bulgaria

Journal of Medical Microbiology, 2009

The aim of this study was to assess the clinical and socio-demographic risk factors for primary H... more The aim of this study was to assess the clinical and socio-demographic risk factors for primary Helicobacter pylori antibacterial resistance. In total, 266 consecutive H. pylori strains, from untreated symptomatic adult patients who answered a questionnaire, were evaluated. Strain susceptibility to amoxicillin, metronidazole, clarithromycin and tetracycline was tested by a breakpoint susceptibility test. Metronidazole resistance was found in fewer (17.0 %) peptic ulcer patients than in non-ulcer subjects (28.3 %, P50.037), as well as in fewer patients born in villages (12.7 %) than in those born in towns (27.6 %, P50.016). Clarithromycin resistance varied from 8.8 to 23.4 % (P50.009) within the hospital centres. The highest clarithromycin resistance rate was found in hospital centre A (23.4 %) compared to other centres (12.9 %, P50.041). The factors sex, age, symptom duration, non-steroidal anti-inflammatory drug use, diabetes, type of profession and educational level were not associated with H. pylori resistance. Logistic regression revealed that the risk factors for metronidazole resistance were non-ulcer disease [odds ratio (OR) 1.95, 95 % confidence interval (95 % CI) 1.04-3.65] and a birthplace of a town (OR 2.64, 95 % CI 1.18-5.93). The hospital centre may be a risk factor (OR 2.07, 95 % CI 1.02-4.21) for clarithromycin resistance but further studies are required to verify this suggestion. In conclusion, the knowledge of the risk factors for H. pylori resistance to antibacterials could facilitate the treatment choice for H. pylori eradication.

Research paper thumbnail of Effect of calcination temperature on the properties of industrial V 2 O 5 -TiO 2 (anatase) catalysts in methanol oxidation

Reaction Kinetics and Catalysis Letters, 2004

The properties of the catalysts for partial oxidation of o-xylene depend on the structure of the ... more The properties of the catalysts for partial oxidation of o-xylene depend on the structure of the supported vanadium sites. The structure itself is strongly dependent on the calcination temperature of the catalyst at which thermal deposition of the metal oxide on the oxide support takes place. We have investigated the effect of calcination temperature on the activity and selectivity of industrial V2O5-TiO2 (anatase) supported catalysts designed for partial oxidation of o-xylene in their application to methanol oxidation.

Research paper thumbnail of Comparison of some haematological parameters between three bird Comparison of some haematological parameters between three bird species from the species from the Columbidae Columbidae family - family - short communication

LASHEV, L., H. HUBENOV, Y. NIKOLOV, V. LASHEVA, R. MIHAILOV: Comparison Comparison of some haemat... more LASHEV, L., H. HUBENOV, Y. NIKOLOV, V. LASHEVA, R. MIHAILOV: Comparison Comparison of some haematological parameters in three bird species from the Columbidae family. Vet. arhiv 79, 409-414, 2009.

Research paper thumbnail of Study of the selectivity of a V 2 O 5 −ZrO 2 catalyst for partial oxidation of o -xylene at high temperatures

Reaction Kinetics and Catalysis Letters, 1999

It has been established that at high temperatures (above 450°C) the V2O5−ZrO2 catalyst exhibits a... more It has been established that at high temperatures (above 450°C) the V2O5−ZrO2 catalyst exhibits a higher selectivity in the oxidation ofo-xylene to phthalic anhydride than does the conventional V2O5−TiO2(a) catalyst. The catalyst selectivity is found to increase with respect to partial oxidation ofo-xylene, the valuable by-product maleic anhydride being obtained. Studies by different physicochemical methods have shown that V2O5−ZrO2 undergoes no significant phase and structural changes under high-temperature conditions.

Research paper thumbnail of Prevalence and evolution of Helicobacter pylori resistance to 6 antibacterial agents over 12 years and correlation between susceptibility testing methods

Diagnostic Microbiology and Infectious Disease, 2008

The aim of this study was to evaluate Helicobacter pylori antibacterial resistance in 2005 to 200... more The aim of this study was to evaluate Helicobacter pylori antibacterial resistance in 2005 to 2007, resistance evolution since 1996 to 1999, and performance of breakpoint susceptibility testing (BST) compared with E test for clarithromycin or agar dilution method (ADM) for metronidazole, amoxicillin, tetracycline, and ciprofloxacin. Resistance in 613 untreated adults, 91 treated adults, and 75 untreated children was 25%, 48.4%, and 16% for metronidazole; 17.8%, 45.1%, and 18.7% for clarithromycin; 4.4%, 13.3%, and 2.7% for tetracycline; and 7.7%, 18.2%, and 6.8% for ciprofloxacin, respectively. Resistance to amoxicillin (0.9%) and nitrofurantoin (1.3%) was uncommon. Three strains (0.4%) exhibited triple resistance to amoxicillin, metronidazole, and clarithromycin. Primary resistance rates in adults and children were comparable. Metronidazole resistance was less common in ulcer adults than in the rest. Primary clarithromycin resistance increased significantly from 10% in 1996 to 1999 to 17.9% in 2005 to 2007. Many strains (26.4%) from treated adults showed resistance to metronidazole and clarithromycin. Category agreement between the BST and E test or ADM results was good (93.3-100%). In conclusion, the increasing clarithromycin resistance and presence of multidrug resistance are worrying. Fluoroquinolones should be used with caution for H. pylori eradication in treated patients.

Research paper thumbnail of дд

Research paper thumbnail of Nonlinear chi(2) and chi(3) spectroscopy of magnesium sulfite hexahydrate single crystal

The second- and third-order nonlinear optical properties of Magnesium Sulfite Hexahydrate (MgSO 3... more The second- and third-order nonlinear optical properties of Magnesium Sulfite Hexahydrate (MgSO 3.6H IIO) were studied by Second-Harmonic Generation (SHG) and Degenerate Four-Wave Mixing (DFWM). Nanosecond pumping by Nd:YAG laser having a variable reflection output coupler was used. The effective quadratic (χ (2)) and cubic (χ (3)) nonlinear susceptibility values are obtained at room temperature. The dispersion of the nonlinear optical susceptibility of MgSO 3.6H IIO is also discussed.

Research paper thumbnail of Herbizidwirkung einiger Thioharnstoffderivate

Archives of Phytopathology and Plant Protection, 1972

Research paper thumbnail of Evaluation of clinical and socio-demographic risk factors for antibacterial resistance of Helicobacter pylori in Bulgaria

Journal of Medical Microbiology, 2009

The aim of this study was to assess the clinical and socio-demographic risk factors for primary H... more The aim of this study was to assess the clinical and socio-demographic risk factors for primary Helicobacter pylori antibacterial resistance. In total, 266 consecutive H. pylori strains, from untreated symptomatic adult patients who answered a questionnaire, were evaluated. Strain susceptibility to amoxicillin, metronidazole, clarithromycin and tetracycline was tested by a breakpoint susceptibility test. Metronidazole resistance was found in fewer (17.0 %) peptic ulcer patients than in non-ulcer subjects (28.3 %, P50.037), as well as in fewer patients born in villages (12.7 %) than in those born in towns (27.6 %, P50.016). Clarithromycin resistance varied from 8.8 to 23.4 % (P50.009) within the hospital centres. The highest clarithromycin resistance rate was found in hospital centre A (23.4 %) compared to other centres (12.9 %, P50.041). The factors sex, age, symptom duration, non-steroidal anti-inflammatory drug use, diabetes, type of profession and educational level were not associated with H. pylori resistance. Logistic regression revealed that the risk factors for metronidazole resistance were non-ulcer disease [odds ratio (OR) 1.95, 95 % confidence interval (95 % CI) 1.04-3.65] and a birthplace of a town (OR 2.64, 95 % CI 1.18-5.93). The hospital centre may be a risk factor (OR 2.07, 95 % CI 1.02-4.21) for clarithromycin resistance but further studies are required to verify this suggestion. In conclusion, the knowledge of the risk factors for H. pylori resistance to antibacterials could facilitate the treatment choice for H. pylori eradication.

Research paper thumbnail of Effect of calcination temperature on the properties of industrial V 2 O 5 -TiO 2 (anatase) catalysts in methanol oxidation

Reaction Kinetics and Catalysis Letters, 2004

The properties of the catalysts for partial oxidation of o-xylene depend on the structure of the ... more The properties of the catalysts for partial oxidation of o-xylene depend on the structure of the supported vanadium sites. The structure itself is strongly dependent on the calcination temperature of the catalyst at which thermal deposition of the metal oxide on the oxide support takes place. We have investigated the effect of calcination temperature on the activity and selectivity of industrial V2O5-TiO2 (anatase) supported catalysts designed for partial oxidation of o-xylene in their application to methanol oxidation.

Research paper thumbnail of Comparison of some haematological parameters between three bird Comparison of some haematological parameters between three bird species from the species from the Columbidae Columbidae family - family - short communication

LASHEV, L., H. HUBENOV, Y. NIKOLOV, V. LASHEVA, R. MIHAILOV: Comparison Comparison of some haemat... more LASHEV, L., H. HUBENOV, Y. NIKOLOV, V. LASHEVA, R. MIHAILOV: Comparison Comparison of some haematological parameters in three bird species from the Columbidae family. Vet. arhiv 79, 409-414, 2009.

Research paper thumbnail of Study of the selectivity of a V 2 O 5 −ZrO 2 catalyst for partial oxidation of o -xylene at high temperatures

Reaction Kinetics and Catalysis Letters, 1999

It has been established that at high temperatures (above 450°C) the V2O5−ZrO2 catalyst exhibits a... more It has been established that at high temperatures (above 450°C) the V2O5−ZrO2 catalyst exhibits a higher selectivity in the oxidation ofo-xylene to phthalic anhydride than does the conventional V2O5−TiO2(a) catalyst. The catalyst selectivity is found to increase with respect to partial oxidation ofo-xylene, the valuable by-product maleic anhydride being obtained. Studies by different physicochemical methods have shown that V2O5−ZrO2 undergoes no significant phase and structural changes under high-temperature conditions.

Research paper thumbnail of Prevalence and evolution of Helicobacter pylori resistance to 6 antibacterial agents over 12 years and correlation between susceptibility testing methods

Diagnostic Microbiology and Infectious Disease, 2008

The aim of this study was to evaluate Helicobacter pylori antibacterial resistance in 2005 to 200... more The aim of this study was to evaluate Helicobacter pylori antibacterial resistance in 2005 to 2007, resistance evolution since 1996 to 1999, and performance of breakpoint susceptibility testing (BST) compared with E test for clarithromycin or agar dilution method (ADM) for metronidazole, amoxicillin, tetracycline, and ciprofloxacin. Resistance in 613 untreated adults, 91 treated adults, and 75 untreated children was 25%, 48.4%, and 16% for metronidazole; 17.8%, 45.1%, and 18.7% for clarithromycin; 4.4%, 13.3%, and 2.7% for tetracycline; and 7.7%, 18.2%, and 6.8% for ciprofloxacin, respectively. Resistance to amoxicillin (0.9%) and nitrofurantoin (1.3%) was uncommon. Three strains (0.4%) exhibited triple resistance to amoxicillin, metronidazole, and clarithromycin. Primary resistance rates in adults and children were comparable. Metronidazole resistance was less common in ulcer adults than in the rest. Primary clarithromycin resistance increased significantly from 10% in 1996 to 1999 to 17.9% in 2005 to 2007. Many strains (26.4%) from treated adults showed resistance to metronidazole and clarithromycin. Category agreement between the BST and E test or ADM results was good (93.3-100%). In conclusion, the increasing clarithromycin resistance and presence of multidrug resistance are worrying. Fluoroquinolones should be used with caution for H. pylori eradication in treated patients.

Research paper thumbnail of дд