Tran Tien - Academia.edu (original) (raw)

Papers by Tran Tien

Heredity, 2002

Aedes aegypti, the main vector of dengue viruses in Asia, displays variation in population densit... more Aedes aegypti, the main vector of dengue viruses in Asia, displays variation in population density over time. The larval habitats of this species being unevenly distributed and transient (depending on cycles of drought and flood), the forces generating temporal variation in gene frequencies in populations are studied. We sampled seven mosquito populations from Ho Chi Minh City (Vietnam) and its suburbs on five occasions between April 1999 and August 2000. We investigated genetic variation by studying isoenzyme and microsatellite polymorphism and susceptibility to a dengue 2 virus strain. Ae. aegypti populations collected during the dry season (January-April) showed genetic differentiation (F(ST) = 0.016, P < 10(-6) for isoenzymes) and showed more differentiated infection rates of the dengue 2 virus. The genetic structure of the population is less marked during the rainy season (F(ST) = 0.081, P < 10(-6)). Thus, environmental factors, such as rainfall and factors related to human activity, such as breeding site density and insecticide treatment, control the genetic structure of Ae. aegypti populations in the short term. The implications of studies of this kind for the design of future control programmes are discussed.

In Vietnam, dengue hemorrhagic fever has been detected since the 1950s. In Southeast Asia, urban ... more In Vietnam, dengue hemorrhagic fever has been detected since the 1950s. In Southeast Asia, urban centers expanded rapidly in an uncontrolled and unplanned way. The Aedes aegypti populations and dengue viruses thrived in these new ecological and demographic settings. The result of these changes was a greatly extended geographic distribution, increased densities of Ae. aegypti and the maintenance of the four dengue serotypes leading to a dramatic increase in dengue transmission. To assess the role of the vector in the changing pattern of the disease in Southeast Asia, we studied the ecology of Ae. aegypti, genetic differentiation, variability in competence as a vector for dengue 2 virus, and resistance to insecticides.

Transactions of The Royal Society of Tropical Medicine and Hygiene, 1999

Aedes aegypti is the principal vector of dengue viruses, responsible for a viral infection that h... more Aedes aegypti is the principal vector of dengue viruses, responsible for a viral infection that has become a major public health concern in Asia. In Viet Nam, dengue haemorrhagic fever was first detected in the 1960s and is now a leading cause of death in childhood. We studied the variability in competence of Ae. aegypti as a vector for dengue 2 virus and genetic differentiation in this mosquito species. Twenty mosquito samples collected in 1998 in Ho Chi Minh City were subjected to oral infection and isoenzyme polymorphism analysis by starch gel electrophoresis. Ae. aegypti populations from the centre of Ho Chi Minh City were genetically differentiated and their infection rates differed from those of populations from the commuter belt. These results have implications for insecticidal control during dengue outbreaks.

Applied Physics Letters, 2006

The waveguides of 650 nm emitting high-power laser diodes are analyzed regarding the presence of ... more The waveguides of 650 nm emitting high-power laser diodes are analyzed regarding the presence of deep level defects by photoelectrical techniques, namely, photocurrent spectroscopy, laser beam induced current, and near-field optical beam induced current ͑NOBIC͒. Deep level configurations in pristine devices and the kinetics of defect creation during device operation are monitored and discussed. The localization of the defects within the epitaxial layer sequence is done by NOBIC. We show that light, which is confined within the laser waveguide, interacts with the deep level defects detected. This demonstrates that the presence of deep level defects directly affects the device properties.

Within the project TRUST a total of about 600 actively cooled high power laser diode bars is anal... more Within the project TRUST a total of about 600 actively cooled high power laser diode bars is analyzed. These devices are packaged by various project partners and by applying different packaging technologies. A number of analytical tools is applied to the devices, among others strain profiling by photocurrent spectroscopy. We present selected results such as the evolution of packaging-induced strains when advancing the technology from indium- to AuSn-soldering. The thermal properties of all devices are screened before the aging experiments by using thermal imaging. This involves monitoring of complete thermal profiles along each bar as well as the identification of "hot" emitters. These statistics turns out to be batch-specific and sensitive to the soldering technology used.

Applied Physics Letters, 2005

+ 49 30 2044975 E-Mail:

Materials Science in Semiconductor Processing, 2006

We discuss strains in high-power diode laser arrays, so-called cm-bars, which serve as a model de... more We discuss strains in high-power diode laser arrays, so-called cm-bars, which serve as a model device for presenting a new methodology for spectroscopic strain analysis in devices. Strain relaxation during device operation as well as the interplay between strain and defects is monitored and quantitatively analyzed. By carrying out an analysis of more than one optical transition in a quantum

Applied Physics Letters, 2006

Thermal tuning properties of passively cooled 808 nm emitting high-power diode laser bars are ana... more Thermal tuning properties of passively cooled 808 nm emitting high-power diode laser bars are analyzed. Data from standard devices packaged on Cu heat sinks and identical devices mounted on expansion-matched Cu-W heat sinks are compared. For a standard device, we find up to one-fifth of the thermal tuning rate of -(0.56+/-0.04) meV K-1 to be caused by pressure tuning driven by the relaxation of compressive packaging-induced stress for increasing temperatures. For devices packaged on expansion-matched heat sinks the observed tuning rate of -(0.46+/-0.01) meV K-1 represents almost the genuine thermal tuning rate of the semiconductor device structure. Thus this technology potentially leads to improved device properties.

Applied Physics Letters, 2005

High-power diode laser bar arrays (808 nm) with very uniform emission properties are inspected by... more High-power diode laser bar arrays (808 nm) with very uniform emission properties are inspected by the laser-beam-induced current technique (LBIC). Setting the excitation energy to 50 meV below the lasing energy, we observe distinctive signatures within the LBIC scans at certain locations on the devices. After 1000 h of high-power operation, we observe degradation at exactly those positions that previously showed a characteristic LBIC signature. A cathodoluminescence analysis reveals that the quantum wells of these anomalous device sections suffer from the existence of spots with reduced luminescence efficiency. Additionally, a concomitant 2.3 meV redshift of the quantum-well cathodoluminescence spectrum is also observed. Our measurements demonstrate the efficiency of the LBIC approach as a screening tool as well as its capacity for predicting device failure well before any degradation of the emission properties is observed.

Applied Physics Letters, 2005

We monitor the mechanical strain evolution with typical use in the quantum well of AlGaAs/GaAs-ba... more We monitor the mechanical strain evolution with typical use in the quantum well of AlGaAs/GaAs-based high-power diode laser arrays (cm bars) by spectroscopic means. We show experimentally that pristine devices are essentially uniaxially compressed along the 110-direction with a strain maximum of -0.16% at the center of the device. At the device edges, almost no packaging-induced strain is detectable. After 500 h of continuous wave operation at a current of I=80 A, the strain is reduced by 50%. Furthermore, we observe the growth of a localized region of compressive strain, of hydrostatic symmetry, in one emitter of a particular cm-bar. A compression of about -0.017% is observed, and is most likely caused by point defect accumulation. Our results demonstrate information about absolute strain values and, at least in part, about strain symmetry as well can be obtained by spectroscopic means even within packaged complex optoelectronic devices.

Heredity, 2002

Aedes aegypti, the main vector of dengue viruses in Asia, displays variation in population densit... more Aedes aegypti, the main vector of dengue viruses in Asia, displays variation in population density over time. The larval habitats of this species being unevenly distributed and transient (depending on cycles of drought and flood), the forces generating temporal variation in gene frequencies in populations are studied. We sampled seven mosquito populations from Ho Chi Minh City (Vietnam) and its suburbs on five occasions between April 1999 and August 2000. We investigated genetic variation by studying isoenzyme and microsatellite polymorphism and susceptibility to a dengue 2 virus strain. Ae. aegypti populations collected during the dry season (January-April) showed genetic differentiation (F(ST) = 0.016, P < 10(-6) for isoenzymes) and showed more differentiated infection rates of the dengue 2 virus. The genetic structure of the population is less marked during the rainy season (F(ST) = 0.081, P < 10(-6)). Thus, environmental factors, such as rainfall and factors related to human activity, such as breeding site density and insecticide treatment, control the genetic structure of Ae. aegypti populations in the short term. The implications of studies of this kind for the design of future control programmes are discussed.

In Vietnam, dengue hemorrhagic fever has been detected since the 1950s. In Southeast Asia, urban ... more In Vietnam, dengue hemorrhagic fever has been detected since the 1950s. In Southeast Asia, urban centers expanded rapidly in an uncontrolled and unplanned way. The Aedes aegypti populations and dengue viruses thrived in these new ecological and demographic settings. The result of these changes was a greatly extended geographic distribution, increased densities of Ae. aegypti and the maintenance of the four dengue serotypes leading to a dramatic increase in dengue transmission. To assess the role of the vector in the changing pattern of the disease in Southeast Asia, we studied the ecology of Ae. aegypti, genetic differentiation, variability in competence as a vector for dengue 2 virus, and resistance to insecticides.

Transactions of The Royal Society of Tropical Medicine and Hygiene, 1999

Aedes aegypti is the principal vector of dengue viruses, responsible for a viral infection that h... more Aedes aegypti is the principal vector of dengue viruses, responsible for a viral infection that has become a major public health concern in Asia. In Viet Nam, dengue haemorrhagic fever was first detected in the 1960s and is now a leading cause of death in childhood. We studied the variability in competence of Ae. aegypti as a vector for dengue 2 virus and genetic differentiation in this mosquito species. Twenty mosquito samples collected in 1998 in Ho Chi Minh City were subjected to oral infection and isoenzyme polymorphism analysis by starch gel electrophoresis. Ae. aegypti populations from the centre of Ho Chi Minh City were genetically differentiated and their infection rates differed from those of populations from the commuter belt. These results have implications for insecticidal control during dengue outbreaks.

Applied Physics Letters, 2006

The waveguides of 650 nm emitting high-power laser diodes are analyzed regarding the presence of ... more The waveguides of 650 nm emitting high-power laser diodes are analyzed regarding the presence of deep level defects by photoelectrical techniques, namely, photocurrent spectroscopy, laser beam induced current, and near-field optical beam induced current ͑NOBIC͒. Deep level configurations in pristine devices and the kinetics of defect creation during device operation are monitored and discussed. The localization of the defects within the epitaxial layer sequence is done by NOBIC. We show that light, which is confined within the laser waveguide, interacts with the deep level defects detected. This demonstrates that the presence of deep level defects directly affects the device properties.

Within the project TRUST a total of about 600 actively cooled high power laser diode bars is anal... more Within the project TRUST a total of about 600 actively cooled high power laser diode bars is analyzed. These devices are packaged by various project partners and by applying different packaging technologies. A number of analytical tools is applied to the devices, among others strain profiling by photocurrent spectroscopy. We present selected results such as the evolution of packaging-induced strains when advancing the technology from indium- to AuSn-soldering. The thermal properties of all devices are screened before the aging experiments by using thermal imaging. This involves monitoring of complete thermal profiles along each bar as well as the identification of "hot" emitters. These statistics turns out to be batch-specific and sensitive to the soldering technology used.

Applied Physics Letters, 2005

+ 49 30 2044975 E-Mail:

Materials Science in Semiconductor Processing, 2006

We discuss strains in high-power diode laser arrays, so-called cm-bars, which serve as a model de... more We discuss strains in high-power diode laser arrays, so-called cm-bars, which serve as a model device for presenting a new methodology for spectroscopic strain analysis in devices. Strain relaxation during device operation as well as the interplay between strain and defects is monitored and quantitatively analyzed. By carrying out an analysis of more than one optical transition in a quantum

Applied Physics Letters, 2006

Thermal tuning properties of passively cooled 808 nm emitting high-power diode laser bars are ana... more Thermal tuning properties of passively cooled 808 nm emitting high-power diode laser bars are analyzed. Data from standard devices packaged on Cu heat sinks and identical devices mounted on expansion-matched Cu-W heat sinks are compared. For a standard device, we find up to one-fifth of the thermal tuning rate of -(0.56+/-0.04) meV K-1 to be caused by pressure tuning driven by the relaxation of compressive packaging-induced stress for increasing temperatures. For devices packaged on expansion-matched heat sinks the observed tuning rate of -(0.46+/-0.01) meV K-1 represents almost the genuine thermal tuning rate of the semiconductor device structure. Thus this technology potentially leads to improved device properties.

Applied Physics Letters, 2005

High-power diode laser bar arrays (808 nm) with very uniform emission properties are inspected by... more High-power diode laser bar arrays (808 nm) with very uniform emission properties are inspected by the laser-beam-induced current technique (LBIC). Setting the excitation energy to 50 meV below the lasing energy, we observe distinctive signatures within the LBIC scans at certain locations on the devices. After 1000 h of high-power operation, we observe degradation at exactly those positions that previously showed a characteristic LBIC signature. A cathodoluminescence analysis reveals that the quantum wells of these anomalous device sections suffer from the existence of spots with reduced luminescence efficiency. Additionally, a concomitant 2.3 meV redshift of the quantum-well cathodoluminescence spectrum is also observed. Our measurements demonstrate the efficiency of the LBIC approach as a screening tool as well as its capacity for predicting device failure well before any degradation of the emission properties is observed.

Applied Physics Letters, 2005

We monitor the mechanical strain evolution with typical use in the quantum well of AlGaAs/GaAs-ba... more We monitor the mechanical strain evolution with typical use in the quantum well of AlGaAs/GaAs-based high-power diode laser arrays (cm bars) by spectroscopic means. We show experimentally that pristine devices are essentially uniaxially compressed along the 110-direction with a strain maximum of -0.16% at the center of the device. At the device edges, almost no packaging-induced strain is detectable. After 500 h of continuous wave operation at a current of I=80 A, the strain is reduced by 50%. Furthermore, we observe the growth of a localized region of compressive strain, of hydrostatic symmetry, in one emitter of a particular cm-bar. A compression of about -0.017% is observed, and is most likely caused by point defect accumulation. Our results demonstrate information about absolute strain values and, at least in part, about strain symmetry as well can be obtained by spectroscopic means even within packaged complex optoelectronic devices.