Irwan De - Academia.edu (original) (raw)

Papers by Irwan De

... Continuous resistivity changes are computed by MT processing prior to Miyake-jima eruption ..... more ... Continuous resistivity changes are computed by MT processing prior to Miyake-jima eruption ... 1990], [Baubron et al., 1991] and [Chiodini et al., 2001]) and may change with time as the result of self-sealing, microfracturation and changes in the stress field ([Harris and Maciejewski ...

In recent years, there has been great progress understanding the underlying causes of earthquakes... more In recent years, there has been great progress understanding the underlying causes of earthquakes, as well as forecasting their occurrence and preparing communities for their damaging effects. Plate tectonic theory explains the occurrence of earthquakes at discrete plate boundaries, such as subduction zones and transform faults, but diffuse plate boundaries are also common. Seismic hazards are distributed over a broad region within diffuse plate boundaries. Intraplate earthquakes occur in otherwise stable crust located far away from any plate boundary, and can cause great loss of life and property. These earthquakes cannot be explained by classical plate tectonics, and as such, are a topic of great scientific debate. Earthquake hazards are determined by a number of factors, among which the earthquake magnitude is only one factor. Other critical factors include population density, the potential for secondary hazards, such as fire, landslides and tsunamis, and the vulnerability of man-made structures to severe strong ground motion. In order to reduce earthquake hazards, engineers and scientists are taking advantage of new technologies to advance the fields of earthquake forecasting and mitigation. Seismicity is effectively monitored in many regions with regional networks, and world seismicity is monitored by the Global Seismic Network that consists of more than 150 high-quality, broadband seismic stations using satellite telemetry systems. Global Positioning Satellite (GPS) systems monitor crustal strain in tectonically active and intraplate regions. A relatively recent technology, Interferometric Synthetic Aperture Radar (InSAR) uses radar waves emitted from satellites to map the Earth’s surface at high (sub-cm) resolution. InSAR technology opens the door to continuous monitoring of crustal deformation within active plate boundaries. The U.S. Geological Survey (USGS), along with other partners, has created ShakeMap, an online notification system that provides near-real-time post-earthquake maps of ground shaking intensity. These maps are especially useful for the coordination of emergency response teams and for the improvement of building codes. Using a combination of these new technologies, with paleoseismology studies, we have steadily improved the science of earthquake forecasting whereby one estimates the probability that an earthquake will occur during a specified time interval. A very recent development is Earthquake Early Warning, a system that will provide earthquake information within seconds of the initial rupture of a fault. These systems will give the public some tens of seconds to prepare for imminent earthquake strong ground motion. Advances in earthquake science hold the promise of diminishing earthquake hazards on a global scale despite ever-increasing population growth.

International Journal of Radiation Oncology Biology Physics, 2005

: A prospective Phase I/II study was undertaken on 44 patients with NSCLC without detectable dist... more : A prospective Phase I/II study was undertaken on 44 patients with NSCLC without detectable distant metastases on CT and FDG-PET scan, delivering either 61.2 Gy in 34 fractions over 23 days or 64.8 Gy in 36 fractions over 24 days (1.8 Gy b.i.d. with 8-h interval). Only the primary tumor and the positive mediastinal areas on the pretreatment FDG-PET scan were irradiated. Isolated nodal failure was defined as recurrence in the regional nodes outside of the clinical target volume, in the absence of in-field failure. Results: The CT and FDG-PET stage distribution was as follows: Stage I: 8 patients (18%) and 13 patients (29%); Stage II: 6 patients (14%) and 10 patients (23%); Stage IIIA: 15 patients (34%) and 7 patients (16%); Stage IIIB: 15 patients (34%) and 14 patients (32%), respectively. After a median follow-up time of 16 months (95% confidence interval [CI], 11-21 months) postradiotherapy, 11 patients (25%) developed a local recurrence. Only 1 patient (crude rate, 2.3%; upper bound of 95% CI, 10.3%), with a Stage II tumor on both CT and PET, developed an isolated nodal failure. The median actuarial overall survival was 21 months (95% CI, 14 -28 months), and the median actuarial progression-free survival was 18 months (95% CI, 12-24 months). Conclusions: Selective mediastinal node irradiation based on FDG-PET scan data in patients with NSCLC results in low isolated nodal failure rates. In the Phase I component of this trial, radiation dose escalation up to 64.8 Gy in 36 fractions over 24 days is feasible.

Irwan Hidayana onderzocht de prevalentie en sociale stigma’s rondom hiv/aids in Karawang, Indones... more Irwan Hidayana onderzocht de prevalentie en sociale stigma’s rondom hiv/aids in Karawang, Indonesië. Hiv/aids vormt in Indonesië een stille epidemie: mensen worden geïnfecteerd zonder te weten dat ze risico lopen. Het huidige beleid is gericht op groepen die relatief veel risico lopen. De dreiging voor de algemene bevolking wordt genegeerd, terwijl recente cijfers laten zien dat juist huisvrouwen in toenemende

European Radiology, 2006

Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine ... more Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8×8×2 cm3 containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm3 were compared. The water content was increased in patients compared with controls (GM: 244±21 vs. 194±10 a.u.; WM: 245±32 vs. 190±11 a.u.), FA decreased (GM: 0.226±0.038 vs. 0.270±0.020; WM: 0.337±0.044 vs. 0.402±0.011) and ADC increased [GM: 1134±203 vs. 899±28 (×10−6 mm2/s); WM: 901±138 vs. 751±17 (×10−6 mm2/s)]. Correlations of water content with FA and ADC in WM were strong (r=−0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=−0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=−0.88; P<0.00001) than in GM (r=−0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue.

We report new observations of the globally threatened Minas Gerais Tyrannulet Phylloscartes roque... more We report new observations of the globally threatened Minas Gerais Tyrannulet Phylloscartes roquettei from two areas in the São Francisco Valley, Minas Gerais, Brazil, between July 1993 and February 2002. Four pairs, one fledged young and two lone individuals were observed in the course of our fieldwork. It was previously known only from a female taken in the mid-1920s and sight records and tape-recordings in 1977. Our records extend the species' known range 250 km south and west of the type-locality region. Details of the first-known male specimen are presented, along with novel data concerning its vocalizations and behaviour. We draw attention to the possible relationship of the species to a group of four other Phylloscartes tyrannulets with similarly patterned faces and overall plumage, which exhibit a similar circum-Amazonian distribution pattern to three Phyllomyias tyrannulets. We also take the opportunity to draw more attention to the imperilled conservation status of the dry forests upon which P. roquettei and a host of other threatened and Near-threatened avian taxa depend.

Psychiatry Research-neuroimaging, 2008

The antidepressant fluoxetine stimulates astrocytic glycogenolysis, which serves as an energy sou... more The antidepressant fluoxetine stimulates astrocytic glycogenolysis, which serves as an energy source for axons. In multiple sclerosis patients fluoxetine administration may improve energy supply in neuron cells and thus inhibit axonal degeneration. In a preliminary pilot study, 15 patients with multiple sclerosis (MS) were examined by diffusion tensor imaging (DTI) and (1)H magnetic resonance spectroscopy (MRS) in order to quantify the brain tissue diffusion properties (fractional anisotropy, apparent diffusion coefficient) and metabolite levels (choline, creatine and N-acetylaspartate) in cortical gray matter brain tissue, in normal appearing white matter and in white matter lesions. After oral administration of fluoxetine (20 mg/day) for 1 week, the DTI and MRS measurements were repeated and after treatment with a higher dose (40 mg/day) during the next week, a third series of DTI/MRS examinations was performed in order to assess any changes in diffusion properties and metabolism. One trend was observed in gray matter tissue, a decrease of choline measured at weeks 1 and 2 (significant in a subgroup of 11 relapsing remitting/secondary progressive MS patients). In white matter lesions, the apparent diffusion coefficient was increased at week 1 and N-acetylaspartate was increased at week 2 (both significant). These preliminary results provide evidence of a neuroprotective effect of fluoxetine in MS by the observed partial normalization of the structure-related MRS parameter N-acetylaspartate in white matter lesions.

European Radiology, 2005

Primary progressive multiple sclerosis (ppMS; n=4) patients and controls (n=4) were examined by 1... more Primary progressive multiple sclerosis (ppMS; n=4) patients and controls (n=4) were examined by 1H magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) in order to map choline (Cho), creatine and N-acetylaspartate (NAA), the fractional anisotropy (FA) and the apparent diffusion constant (ADC). After chemical shift imaging (point-resolved spectroscopy, repetition time/echo time 1,500 ms/135 ms) of a supraventricular volume of interest of 8×8×2 cm3 (64 voxels) MRS peak areas were matched to the results of DTI for the corresponding volume elements. Mean FA and NAA values were reduced in the ppMS patients (P<0.01, both) and the ADC increased (P<0.02). The spatial distribution of NAA showed strong correlation to ADC in both ppMS patients and controls (r =−0.74 and r= −0.70; P<0.00001, both), and weaker correlations to FA (r=0.49 and r=0.41; P<0.00001, all). FA and ADC also correlated significantly with Cho in patients and controls (P<0.00001, all). The relationship of Cho and NAA to the ADC and the FA and thus to the content of neuronal structures suggests that these metabolite signals essentially originate from axons (NAA) and the myelin sheath (Cho). This is of interest in view of previous reports in which Cho increases were associated with demyelination and the subsequent breakdown of neurons.

Journal of Volcanology and Geothermal Research, 2006

Merapi volcano (Java, Indonesia) is in almost continuous activity with growth of an andesitic lav... more Merapi volcano (Java, Indonesia) is in almost continuous activity with growth of an andesitic lava dome. This dome frequently collapses to form potentially deadly glowing avalanches, explosions and nuées ardentes. To monitor the evolution of surface displacements and to model the associated magmatic sources, we established a Global Positioning System (GPS) network in 1993 and have measured it each year using the static GPS method. However, the limited number of benchmarks and the geometry of the network did not allow us to precisely locate major mechanical discontinuities within the edifice. Precisely locating these discontinuities is of central importance because they delimit areas of potential instability and provide means to evaluate potential volumes of falling material.

... Continuous resistivity changes are computed by MT processing prior to Miyake-jima eruption ..... more ... Continuous resistivity changes are computed by MT processing prior to Miyake-jima eruption ... 1990], [Baubron et al., 1991] and [Chiodini et al., 2001]) and may change with time as the result of self-sealing, microfracturation and changes in the stress field ([Harris and Maciejewski ...

In recent years, there has been great progress understanding the underlying causes of earthquakes... more In recent years, there has been great progress understanding the underlying causes of earthquakes, as well as forecasting their occurrence and preparing communities for their damaging effects. Plate tectonic theory explains the occurrence of earthquakes at discrete plate boundaries, such as subduction zones and transform faults, but diffuse plate boundaries are also common. Seismic hazards are distributed over a broad region within diffuse plate boundaries. Intraplate earthquakes occur in otherwise stable crust located far away from any plate boundary, and can cause great loss of life and property. These earthquakes cannot be explained by classical plate tectonics, and as such, are a topic of great scientific debate. Earthquake hazards are determined by a number of factors, among which the earthquake magnitude is only one factor. Other critical factors include population density, the potential for secondary hazards, such as fire, landslides and tsunamis, and the vulnerability of man-made structures to severe strong ground motion. In order to reduce earthquake hazards, engineers and scientists are taking advantage of new technologies to advance the fields of earthquake forecasting and mitigation. Seismicity is effectively monitored in many regions with regional networks, and world seismicity is monitored by the Global Seismic Network that consists of more than 150 high-quality, broadband seismic stations using satellite telemetry systems. Global Positioning Satellite (GPS) systems monitor crustal strain in tectonically active and intraplate regions. A relatively recent technology, Interferometric Synthetic Aperture Radar (InSAR) uses radar waves emitted from satellites to map the Earth’s surface at high (sub-cm) resolution. InSAR technology opens the door to continuous monitoring of crustal deformation within active plate boundaries. The U.S. Geological Survey (USGS), along with other partners, has created ShakeMap, an online notification system that provides near-real-time post-earthquake maps of ground shaking intensity. These maps are especially useful for the coordination of emergency response teams and for the improvement of building codes. Using a combination of these new technologies, with paleoseismology studies, we have steadily improved the science of earthquake forecasting whereby one estimates the probability that an earthquake will occur during a specified time interval. A very recent development is Earthquake Early Warning, a system that will provide earthquake information within seconds of the initial rupture of a fault. These systems will give the public some tens of seconds to prepare for imminent earthquake strong ground motion. Advances in earthquake science hold the promise of diminishing earthquake hazards on a global scale despite ever-increasing population growth.

International Journal of Radiation Oncology Biology Physics, 2005

: A prospective Phase I/II study was undertaken on 44 patients with NSCLC without detectable dist... more : A prospective Phase I/II study was undertaken on 44 patients with NSCLC without detectable distant metastases on CT and FDG-PET scan, delivering either 61.2 Gy in 34 fractions over 23 days or 64.8 Gy in 36 fractions over 24 days (1.8 Gy b.i.d. with 8-h interval). Only the primary tumor and the positive mediastinal areas on the pretreatment FDG-PET scan were irradiated. Isolated nodal failure was defined as recurrence in the regional nodes outside of the clinical target volume, in the absence of in-field failure. Results: The CT and FDG-PET stage distribution was as follows: Stage I: 8 patients (18%) and 13 patients (29%); Stage II: 6 patients (14%) and 10 patients (23%); Stage IIIA: 15 patients (34%) and 7 patients (16%); Stage IIIB: 15 patients (34%) and 14 patients (32%), respectively. After a median follow-up time of 16 months (95% confidence interval [CI], 11-21 months) postradiotherapy, 11 patients (25%) developed a local recurrence. Only 1 patient (crude rate, 2.3%; upper bound of 95% CI, 10.3%), with a Stage II tumor on both CT and PET, developed an isolated nodal failure. The median actuarial overall survival was 21 months (95% CI, 14 -28 months), and the median actuarial progression-free survival was 18 months (95% CI, 12-24 months). Conclusions: Selective mediastinal node irradiation based on FDG-PET scan data in patients with NSCLC results in low isolated nodal failure rates. In the Phase I component of this trial, radiation dose escalation up to 64.8 Gy in 36 fractions over 24 days is feasible.

Irwan Hidayana onderzocht de prevalentie en sociale stigma’s rondom hiv/aids in Karawang, Indones... more Irwan Hidayana onderzocht de prevalentie en sociale stigma’s rondom hiv/aids in Karawang, Indonesië. Hiv/aids vormt in Indonesië een stille epidemie: mensen worden geïnfecteerd zonder te weten dat ze risico lopen. Het huidige beleid is gericht op groepen die relatief veel risico lopen. De dreiging voor de algemene bevolking wordt genegeerd, terwijl recente cijfers laten zien dat juist huisvrouwen in toenemende

European Radiology, 2006

Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine ... more Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8×8×2 cm3 containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm3 were compared. The water content was increased in patients compared with controls (GM: 244±21 vs. 194±10 a.u.; WM: 245±32 vs. 190±11 a.u.), FA decreased (GM: 0.226±0.038 vs. 0.270±0.020; WM: 0.337±0.044 vs. 0.402±0.011) and ADC increased [GM: 1134±203 vs. 899±28 (×10−6 mm2/s); WM: 901±138 vs. 751±17 (×10−6 mm2/s)]. Correlations of water content with FA and ADC in WM were strong (r=−0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=−0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=−0.88; P<0.00001) than in GM (r=−0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue.

We report new observations of the globally threatened Minas Gerais Tyrannulet Phylloscartes roque... more We report new observations of the globally threatened Minas Gerais Tyrannulet Phylloscartes roquettei from two areas in the São Francisco Valley, Minas Gerais, Brazil, between July 1993 and February 2002. Four pairs, one fledged young and two lone individuals were observed in the course of our fieldwork. It was previously known only from a female taken in the mid-1920s and sight records and tape-recordings in 1977. Our records extend the species' known range 250 km south and west of the type-locality region. Details of the first-known male specimen are presented, along with novel data concerning its vocalizations and behaviour. We draw attention to the possible relationship of the species to a group of four other Phylloscartes tyrannulets with similarly patterned faces and overall plumage, which exhibit a similar circum-Amazonian distribution pattern to three Phyllomyias tyrannulets. We also take the opportunity to draw more attention to the imperilled conservation status of the dry forests upon which P. roquettei and a host of other threatened and Near-threatened avian taxa depend.

Psychiatry Research-neuroimaging, 2008

The antidepressant fluoxetine stimulates astrocytic glycogenolysis, which serves as an energy sou... more The antidepressant fluoxetine stimulates astrocytic glycogenolysis, which serves as an energy source for axons. In multiple sclerosis patients fluoxetine administration may improve energy supply in neuron cells and thus inhibit axonal degeneration. In a preliminary pilot study, 15 patients with multiple sclerosis (MS) were examined by diffusion tensor imaging (DTI) and (1)H magnetic resonance spectroscopy (MRS) in order to quantify the brain tissue diffusion properties (fractional anisotropy, apparent diffusion coefficient) and metabolite levels (choline, creatine and N-acetylaspartate) in cortical gray matter brain tissue, in normal appearing white matter and in white matter lesions. After oral administration of fluoxetine (20 mg/day) for 1 week, the DTI and MRS measurements were repeated and after treatment with a higher dose (40 mg/day) during the next week, a third series of DTI/MRS examinations was performed in order to assess any changes in diffusion properties and metabolism. One trend was observed in gray matter tissue, a decrease of choline measured at weeks 1 and 2 (significant in a subgroup of 11 relapsing remitting/secondary progressive MS patients). In white matter lesions, the apparent diffusion coefficient was increased at week 1 and N-acetylaspartate was increased at week 2 (both significant). These preliminary results provide evidence of a neuroprotective effect of fluoxetine in MS by the observed partial normalization of the structure-related MRS parameter N-acetylaspartate in white matter lesions.

European Radiology, 2005

Primary progressive multiple sclerosis (ppMS; n=4) patients and controls (n=4) were examined by 1... more Primary progressive multiple sclerosis (ppMS; n=4) patients and controls (n=4) were examined by 1H magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) in order to map choline (Cho), creatine and N-acetylaspartate (NAA), the fractional anisotropy (FA) and the apparent diffusion constant (ADC). After chemical shift imaging (point-resolved spectroscopy, repetition time/echo time 1,500 ms/135 ms) of a supraventricular volume of interest of 8×8×2 cm3 (64 voxels) MRS peak areas were matched to the results of DTI for the corresponding volume elements. Mean FA and NAA values were reduced in the ppMS patients (P<0.01, both) and the ADC increased (P<0.02). The spatial distribution of NAA showed strong correlation to ADC in both ppMS patients and controls (r =−0.74 and r= −0.70; P<0.00001, both), and weaker correlations to FA (r=0.49 and r=0.41; P<0.00001, all). FA and ADC also correlated significantly with Cho in patients and controls (P<0.00001, all). The relationship of Cho and NAA to the ADC and the FA and thus to the content of neuronal structures suggests that these metabolite signals essentially originate from axons (NAA) and the myelin sheath (Cho). This is of interest in view of previous reports in which Cho increases were associated with demyelination and the subsequent breakdown of neurons.

Journal of Volcanology and Geothermal Research, 2006

Merapi volcano (Java, Indonesia) is in almost continuous activity with growth of an andesitic lav... more Merapi volcano (Java, Indonesia) is in almost continuous activity with growth of an andesitic lava dome. This dome frequently collapses to form potentially deadly glowing avalanches, explosions and nuées ardentes. To monitor the evolution of surface displacements and to model the associated magmatic sources, we established a Global Positioning System (GPS) network in 1993 and have measured it each year using the static GPS method. However, the limited number of benchmarks and the geometry of the network did not allow us to precisely locate major mechanical discontinuities within the edifice. Precisely locating these discontinuities is of central importance because they delimit areas of potential instability and provide means to evaluate potential volumes of falling material.