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Papers by Nguyen Duc

Research paper thumbnail of Nonlinear buckling and post-buckling of eccentrically stiffened functionally graded cylindrical shells surrounded by an elastic medium based on the first order shear deformation theory

Vietnam Journal of Mechanics, 2013

In this paper, the nonlinear buckling and post-buckling of an eccentrically stiffened cylindrical... more In this paper, the nonlinear buckling and post-buckling of an eccentrically stiffened cylindrical shell made of functionally graded materials, surrounded by an elastic medium and subjected to mechanical compressive loads and external pressures are investigated by an analytical approach. The cylindrical shells are reinforced by longitudinal and circumferential stiffeners. The material properties of cylindrical shells are graded in the thickness direction according to a volume fraction power-law distribution. The nonlinear stability equations for stiffened cylindrical shells are derived by using the first order shear deformation theory and smeared stiffeners technique. Closed-form expressions for determining the buckling load and load-deflection curves are obtained. The effectiveness of stiffeners in enhancing the stability of cylindrical shells is shown. The effects of volume fraction indexes, material properties, geometrical parameters and foundation parameters are analyzed in detail.

Research paper thumbnail of Oleanane and ursane glycosides from Schefflera octophylla

Phytochemistry, 1994

Twelve triterpene glycosides were isolated from the bark of Schefflera octophylla of Vietnamese o... more Twelve triterpene glycosides were isolated from the bark of Schefflera octophylla of Vietnamese origin. Three of them were identified as asiaticoside, cauloside D and 3a-hydroxyurs-12-ene-23,28-dioic acid 28-O+Lrhamnopyranosyl(1+4)-/?-D-glucopyranosyl(1+6)-P-D-glucopyranoside. The structures of nine new glycosides were elucidated by chemical and spectroscopic evidence. Including the known compounds, the 12 glycosides consisted of six pairs of corresponding ursene and oleanene glycosides and all of them had the same triose moiety at the C-28 position. The names scheffurosides A-F and scheffoleosides B-F were proposed for corresponding pairs of ursene and oleanene glycosides, respectively.

Research paper thumbnail of Crude sponin extracted from Vietnamese ginseng and its major constituent majonoside-R2 attenuate the psychological stress- and foot-shock stress-induced antinociception in mice

Pharmacology Biochemistry and Behavior, 1995

Crude saponin extracted from Vietnamese ginseng and ifs major constituent majonoside-R2 attenuate... more Crude saponin extracted from Vietnamese ginseng and ifs major constituent majonoside-R2 attenuate psychological stressandfoot shock stress-induced antinociception in mice. PHARMACOL BIOCHEM BEHAV 52(2) 427-432, 1995.-Effects of Vietnamese ginseng (VG) crude saponin and majonoside-R2, a major saponin constituent, on the psychological stress-and foot shock stress-induced antinociception in the tail pinch test were examined in mice. VG crude saponin (6.2, 12.5, and 25 mg/kg, PO) attenuated psychological stress-but not foot shock stress-induced antinociceptive response, whereas majonoside-R2 (3, 6.2, and 12.5 mg/kg, PO and IP), as well as naloxone (2 mg/kg, IP), suppressed both psychological stress-and foot shock stress-induced antinociception. Pretreatment with the crude saponin (12.5 mg/kg, PO) or majonoside-R2 (6.2 mg/ kg, PO) for 5 days followed by the treatment in combination with stress for next 5 days did not affect the development of adaptation to foot shock stress, but they significantly suppressed the antinociceptive action of the stress measured on the first, second, and third day during the stress exposure period. Majonoside-R2 (6.2 mg/kg, PO) but not the crude saponin (12.5 mg/ kg, PO) significantly blocked the development of adaptation to psychological stress. These results suggest that VG crude saponin has the suppressing effect on psychological stress-and foot shock stress-induced antinociception and that majonoside-R2 is important for the action of the saponin.

Research paper thumbnail of Effects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice

Pharmacology Biochemistry and Behavior, 1996

fects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice... more fects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice. PHARMACOL BIO-CHEM BEHAV 53(4) 957-963, 1996.-The effects of Vietnamese ginseng (VG) and its major constituent majonoside-R2 on pentobarbital-induced sleep and gastric lesion in psychologically stressed mice were examined. Psychological stress exposure for 30 min significantly decreased the duration of pentobarbital(50 mg/kg, IP)-induced sleep in mice. VG extract (50 mg/kg, PO), VG saponin (25 mg/kg, PO), and majonoside-12 (3.1-12.5 mg/kg, PO and IP) had no effect on pentobarbital sleep in unstressed control mice, but these drugs significantly recovered pentobarbital sleep decreased by psychological stress to the level of unstressed control animals. On the other hand, Punux ginseng (PG) extract (SO-100 mg/kg, PO) failed to affect pentobarbital sleep in psychologically stressed mice. The effect of majonoside-R2 on psychological stress-induced decrease in the hypnotic activity of pentobarbital was significantly blocked by flumazenil (1 mg/kg, IV), a selective benzodiazepine antagonist. Diazepam (0. I mg/kg, IP) significantly prolonged pentobarbital sleep in unstressed and psychologically stressed groups, and the effect of diazepam was significantly attenuated by the same dose of flumazenil. Naloxone (0.5-5 mg/kg, IP), an opioid antagonist, had no effect on pentobarbital sleep in unstressed or psychologically stressed animals. Psychological stress exposure for 16 h caused gastric lesion in mice. VG extract (25-50 mg/kg, PO) and majonoside-R2 (6.2-12.5 mg/kg, PO), as well as diazepam and naloxone, produced the protective action on gastric lesion in psychologically stressed mice. These results suggest that VG and its major constituent majonoside-12 have the protective effects on the psychological stress-induced pathophysiological changes and that benzodiazepine receptors are partly implicated in the effects of majonoside-R2. Psychological stress Vietnamese ginseng extract Pentobarbital-induced sleep Gastric lesion Vietnamese ginseng total saponin Majonoside-R2 ' To whom requests for reprints should be addressed.

Research paper thumbnail of The Possible Involvement of GABAA Systems in the Antinarcotic Effect of Majonoside-R2, a Major Constituent of Vietnamese Ginseng, in Mice

Japanese Journal of Pharmacology, 1996

The effect of majonoside-R2 on morphine and U-50,488H-induced antinociception was examined by the... more The effect of majonoside-R2 on morphine and U-50,488H-induced antinociception was examined by the tail-pinch test in mice and compared with that of diazepam. Majonoside-R2 and diazepam inhibited the morphine and U-50,488H-induced antinociception, and the actions were antagonized by the benzodiazepine receptor antagonist flumazenil and the GABA-gated Cl-channel blocker picrotoxin. Diazepam but not majonoside-R2 exhibited a protective activity against convulsion caused by the GABAA antagonists bicuculline and picrotoxin. These results indicate that GABAA systems are involved in the effect of majonoside-R2 on the opioid-induced antinociception and suggest that the mechanisms of action of majonoside-R2 may differ from those of diazepam.

Research paper thumbnail of Status of Cancer Pain in Hanoi, Vietnam: A Hospital-Wide Survey in a Tertiary Cancer Treatment Center

Journal of Pain and Symptom Management, 2006

Little is known about the prevalence of cancer pain in many developing countries. We report a hos... more Little is known about the prevalence of cancer pain in many developing countries. We report a hospital-wide survey of pain in a tertiary cancer center in Hanoi, Vietnam. All inpatients and outpatients age 18 years or older were approached for participation in the study. Data were collected using the Brief Pain Inventory. Results showed a 70% response rate. Prevalence of moderate to severe pain was 50% (89/178), with 23% reporting severe ratings of pain at its ''worst'' and 33% reporting severe impairment in their ability to work due to pain. Only 1% and 40% reported total and partial pain relief from medications, respectively. This study is among the first to provide a representative view of pain in a tertiary cancer treatment center in Hanoi, Vietnam. The findings provide empirical support for the need for better programmatic efforts to improve relief of cancer pain in developing countries, including Vietnam.

Research paper thumbnail of ISDN Terminals and Integrated Services Delivery

IEEE Journal on Selected Areas in Communications, 1986

This paper proposes that the end user's perception of an "ISDN service" should reflect'three inte... more This paper proposes that the end user's perception of an "ISDN service" should reflect'three interrelated ISDN aspects, namely: ISDN terminal capabilities, ISDN access capabilities, and ISDN network capabilities. Emphasis is placed on the ISDN terminal capabilities in supporting integrated services delivery of different levels to the end user (e.&, integrated bearer services and integrated teleservices delivery). Such a concept, integrated services delivery, is seen to suggest a useful framework for developing a wide range of possible ISDN commercial service/ product offerings. An ISDN service scenario is also described to illustrate some important communication capabilities made possible by an ISDN environment.

Research paper thumbnail of Nonlinear buckling and post-buckling of eccentrically stiffened functionally graded cylindrical shells surrounded by an elastic medium based on the first order shear deformation theory

Vietnam Journal of Mechanics, 2013

In this paper, the nonlinear buckling and post-buckling of an eccentrically stiffened cylindrical... more In this paper, the nonlinear buckling and post-buckling of an eccentrically stiffened cylindrical shell made of functionally graded materials, surrounded by an elastic medium and subjected to mechanical compressive loads and external pressures are investigated by an analytical approach. The cylindrical shells are reinforced by longitudinal and circumferential stiffeners. The material properties of cylindrical shells are graded in the thickness direction according to a volume fraction power-law distribution. The nonlinear stability equations for stiffened cylindrical shells are derived by using the first order shear deformation theory and smeared stiffeners technique. Closed-form expressions for determining the buckling load and load-deflection curves are obtained. The effectiveness of stiffeners in enhancing the stability of cylindrical shells is shown. The effects of volume fraction indexes, material properties, geometrical parameters and foundation parameters are analyzed in detail.

Research paper thumbnail of Oleanane and ursane glycosides from Schefflera octophylla

Phytochemistry, 1994

Twelve triterpene glycosides were isolated from the bark of Schefflera octophylla of Vietnamese o... more Twelve triterpene glycosides were isolated from the bark of Schefflera octophylla of Vietnamese origin. Three of them were identified as asiaticoside, cauloside D and 3a-hydroxyurs-12-ene-23,28-dioic acid 28-O+Lrhamnopyranosyl(1+4)-/?-D-glucopyranosyl(1+6)-P-D-glucopyranoside. The structures of nine new glycosides were elucidated by chemical and spectroscopic evidence. Including the known compounds, the 12 glycosides consisted of six pairs of corresponding ursene and oleanene glycosides and all of them had the same triose moiety at the C-28 position. The names scheffurosides A-F and scheffoleosides B-F were proposed for corresponding pairs of ursene and oleanene glycosides, respectively.

Research paper thumbnail of Crude sponin extracted from Vietnamese ginseng and its major constituent majonoside-R2 attenuate the psychological stress- and foot-shock stress-induced antinociception in mice

Pharmacology Biochemistry and Behavior, 1995

Crude saponin extracted from Vietnamese ginseng and ifs major constituent majonoside-R2 attenuate... more Crude saponin extracted from Vietnamese ginseng and ifs major constituent majonoside-R2 attenuate psychological stressandfoot shock stress-induced antinociception in mice. PHARMACOL BIOCHEM BEHAV 52(2) 427-432, 1995.-Effects of Vietnamese ginseng (VG) crude saponin and majonoside-R2, a major saponin constituent, on the psychological stress-and foot shock stress-induced antinociception in the tail pinch test were examined in mice. VG crude saponin (6.2, 12.5, and 25 mg/kg, PO) attenuated psychological stress-but not foot shock stress-induced antinociceptive response, whereas majonoside-R2 (3, 6.2, and 12.5 mg/kg, PO and IP), as well as naloxone (2 mg/kg, IP), suppressed both psychological stress-and foot shock stress-induced antinociception. Pretreatment with the crude saponin (12.5 mg/kg, PO) or majonoside-R2 (6.2 mg/ kg, PO) for 5 days followed by the treatment in combination with stress for next 5 days did not affect the development of adaptation to foot shock stress, but they significantly suppressed the antinociceptive action of the stress measured on the first, second, and third day during the stress exposure period. Majonoside-R2 (6.2 mg/kg, PO) but not the crude saponin (12.5 mg/ kg, PO) significantly blocked the development of adaptation to psychological stress. These results suggest that VG crude saponin has the suppressing effect on psychological stress-and foot shock stress-induced antinociception and that majonoside-R2 is important for the action of the saponin.

Research paper thumbnail of Effects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice

Pharmacology Biochemistry and Behavior, 1996

fects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice... more fects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice. PHARMACOL BIO-CHEM BEHAV 53(4) 957-963, 1996.-The effects of Vietnamese ginseng (VG) and its major constituent majonoside-R2 on pentobarbital-induced sleep and gastric lesion in psychologically stressed mice were examined. Psychological stress exposure for 30 min significantly decreased the duration of pentobarbital(50 mg/kg, IP)-induced sleep in mice. VG extract (50 mg/kg, PO), VG saponin (25 mg/kg, PO), and majonoside-12 (3.1-12.5 mg/kg, PO and IP) had no effect on pentobarbital sleep in unstressed control mice, but these drugs significantly recovered pentobarbital sleep decreased by psychological stress to the level of unstressed control animals. On the other hand, Punux ginseng (PG) extract (SO-100 mg/kg, PO) failed to affect pentobarbital sleep in psychologically stressed mice. The effect of majonoside-R2 on psychological stress-induced decrease in the hypnotic activity of pentobarbital was significantly blocked by flumazenil (1 mg/kg, IV), a selective benzodiazepine antagonist. Diazepam (0. I mg/kg, IP) significantly prolonged pentobarbital sleep in unstressed and psychologically stressed groups, and the effect of diazepam was significantly attenuated by the same dose of flumazenil. Naloxone (0.5-5 mg/kg, IP), an opioid antagonist, had no effect on pentobarbital sleep in unstressed or psychologically stressed animals. Psychological stress exposure for 16 h caused gastric lesion in mice. VG extract (25-50 mg/kg, PO) and majonoside-R2 (6.2-12.5 mg/kg, PO), as well as diazepam and naloxone, produced the protective action on gastric lesion in psychologically stressed mice. These results suggest that VG and its major constituent majonoside-12 have the protective effects on the psychological stress-induced pathophysiological changes and that benzodiazepine receptors are partly implicated in the effects of majonoside-R2. Psychological stress Vietnamese ginseng extract Pentobarbital-induced sleep Gastric lesion Vietnamese ginseng total saponin Majonoside-R2 ' To whom requests for reprints should be addressed.

Research paper thumbnail of The Possible Involvement of GABAA Systems in the Antinarcotic Effect of Majonoside-R2, a Major Constituent of Vietnamese Ginseng, in Mice

Japanese Journal of Pharmacology, 1996

The effect of majonoside-R2 on morphine and U-50,488H-induced antinociception was examined by the... more The effect of majonoside-R2 on morphine and U-50,488H-induced antinociception was examined by the tail-pinch test in mice and compared with that of diazepam. Majonoside-R2 and diazepam inhibited the morphine and U-50,488H-induced antinociception, and the actions were antagonized by the benzodiazepine receptor antagonist flumazenil and the GABA-gated Cl-channel blocker picrotoxin. Diazepam but not majonoside-R2 exhibited a protective activity against convulsion caused by the GABAA antagonists bicuculline and picrotoxin. These results indicate that GABAA systems are involved in the effect of majonoside-R2 on the opioid-induced antinociception and suggest that the mechanisms of action of majonoside-R2 may differ from those of diazepam.

Research paper thumbnail of Status of Cancer Pain in Hanoi, Vietnam: A Hospital-Wide Survey in a Tertiary Cancer Treatment Center

Journal of Pain and Symptom Management, 2006

Little is known about the prevalence of cancer pain in many developing countries. We report a hos... more Little is known about the prevalence of cancer pain in many developing countries. We report a hospital-wide survey of pain in a tertiary cancer center in Hanoi, Vietnam. All inpatients and outpatients age 18 years or older were approached for participation in the study. Data were collected using the Brief Pain Inventory. Results showed a 70% response rate. Prevalence of moderate to severe pain was 50% (89/178), with 23% reporting severe ratings of pain at its ''worst'' and 33% reporting severe impairment in their ability to work due to pain. Only 1% and 40% reported total and partial pain relief from medications, respectively. This study is among the first to provide a representative view of pain in a tertiary cancer treatment center in Hanoi, Vietnam. The findings provide empirical support for the need for better programmatic efforts to improve relief of cancer pain in developing countries, including Vietnam.

Research paper thumbnail of ISDN Terminals and Integrated Services Delivery

IEEE Journal on Selected Areas in Communications, 1986

This paper proposes that the end user's perception of an "ISDN service" should reflect'three inte... more This paper proposes that the end user's perception of an "ISDN service" should reflect'three interrelated ISDN aspects, namely: ISDN terminal capabilities, ISDN access capabilities, and ISDN network capabilities. Emphasis is placed on the ISDN terminal capabilities in supporting integrated services delivery of different levels to the end user (e.&, integrated bearer services and integrated teleservices delivery). Such a concept, integrated services delivery, is seen to suggest a useful framework for developing a wide range of possible ISDN commercial service/ product offerings. An ISDN service scenario is also described to illustrate some important communication capabilities made possible by an ISDN environment.