Nelson Saona Cardenas - Academia.edu (original) (raw)

Papers by Nelson Saona Cardenas

Colombia Medica, 1969

Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) ... more Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) de pacientes que fallecieron por la infección con VIH-SIDA. Metodología: Estudio retrospectivo de autopsias del 1 de enero de 2004 al 31 de diciembre de 2007 en un hospital público de tercer nivel en la ciudad de Bucaramanga, Santander. Resultados: El hallazgo neuropatológico más común en pacientes que fallecieron por la infección VIH-SIDA fue toxoplasmosis cerebral, 17 casos (28.3%) luego criptococosis cerebral, 7 casos (11.6%), tuberculosis del SNC, 3 casos (5%), encefalopatía por HIV, 2 casos (3.3%), meningitis piógena, un caso (1.6%) y hallazgos inespecíficos,2 casos (3.3%). No hubo lesiones neoplásicas, infecciones por citomegalovirus, herpes, histoplasmosis ni leucoencefalopatía multifocal progresiva (LMP) en ninguno de los casos. En el presente estudio se encontraron cambios en el SNC en 32 casos (53.1%), que, después del respiratorio (39-65%), fue el sistema más afectado por las complicaciones relacionadas con la enfermedad por VIH. La presencia de lesión directa (encefalitis por HIV) y al mismo tiempo infección oportunista se encontró sólo en un caso (1.6%). Conclusiones: En Bucaramanga las infecciones oportunistas fueron las complicaciones más frecuentes y graves a nivel del SNC en los enfermos con VIH-SIDA, de ellas la toxoplasmosis cerebral fue la que más comprometió el SNC de los pacientes con infección con VIH-SIDA, y se expresó morfológicamente como una meningoencefalitis necrosante, ubicada de manera preferencial en la región de los ganglios basales.

Optical Interactions with Tissue and Cells XXII, 2011

Red blood cells (RBC) possess unique viscoelastic characteristics which allow them to pass throug... more Red blood cells (RBC) possess unique viscoelastic characteristics which allow them to pass through capillaries narrower than their size. Measurement of viscoelastic property of cells (e.g. RBC) in low-force regime is of high significance as it represents conditions of membrane fluctuation in response to physiological conditions. Estimation of visco-elastic properties of RBC requires measurement of extent of deformation in RBC

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IX, 2011

While optical tweezers have been widely used for the manipulation and organization of microscopic... more While optical tweezers have been widely used for the manipulation and organization of microscopic objects in three dimensions, observing the manipulated objects along axial direction has been quite challenging. In order to visualize organization and orientation of objects along axial direction, we report development of a Digital holographic microscopy combined with optical tweezers. Digital holography is achieved by use of

Complex Light and Optical Forces V, 2011

High throughput analysis of trapped samples requires effective loading and unloading into the tra... more High throughput analysis of trapped samples requires effective loading and unloading into the trap in a microfluidic environment. We demonstrate development of a hybrid optical transport trap (HOTT) which combines a tapered fiberoptic 2D trap for transport of microscopic objects into and out of the optical tweezers trap in an orthogonal geometry. For small cone angle of the tip, the

Mammalian Biology, 2010

Habitat loss is one of the most important causes of biodiversity loss in South American temperate... more Habitat loss is one of the most important causes of biodiversity loss in South American temperate rainforests, where many endemic species exist. Among these is the monito del monte (Dromiciops gliroides), an arboreal marsupial with restricted distribution, and the only extant species of the order Microbiotheria. Current knowledge about monito del monte habitat use and its responses to human disturbances is scarce. To help fill this gap we investigated its habitat use and selection patterns in a fragmented landscape in southern Chile. Monito del monte individuals were abundant in a large and a small fragment, but rare or undetected in forest strips. Using telemetry data from 12 neighboring individuals in a large fragment and 2 individuals in a small fragment, we estimated their mean home range size of 1.6 ha70.6 (1SD). Monitos del monte had a spatial overlap among individuals of 5074%. Tracked individuals used old-and second-growth habitats as available, did not use the prairie habitats, and strongly avoided the scrublands. In the large fragment we estimated a relative population density of 2175 individuals/ha (mean71SD), whereas in the small fragment it was of 1976 individuals/ha. This is, to our knowledge, the first study of the spatial ecology of the monito del monte based on telemetry data, and evidence presented here could have conservation and planning implications, not only for the target species but also its habitat.

Communications in Computer and Information Science, 2008

This paper presents a new routing protocol to Wireless Sensor Networks called SHRP. This protocol... more This paper presents a new routing protocol to Wireless Sensor Networks called SHRP. This protocol has as principal goal the saving of energy and also provides reliability of data delivery. It is a novel proposal as it acts as a proactive protocol in respect to the choosing of routes, taking in consideration just nodes that can contribute to extend the network lifetime, that means, good battery status and good link quality. It also contributes to network management advising a central point about a possible disconnection of a node caused by low battery or large interference periods. Data messages can be added during the forwarding task and redundant sensing data are not sent, so it contributes again with the energy saving. We show that SHRP has a low time of convergence, which means that reacts quickly in case of topology changes, which is common in Wireless Sensor Networks, as the battery lifetime is low and the environment of wireless network uses to suffer from interferences and obstacles.

Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XVIII, 2011

Atomic Force Microscope (AFM) imaging, due to the scanning method of recording, requires signific... more Atomic Force Microscope (AFM) imaging, due to the scanning method of recording, requires significant recording time for examination of wide sample area. In contrast, digital holographic microscopy (DHM), owing to the wide-field method, allows recording of the hologram in very fast rate which could be numerically analyzed to reveal surface of the sample with axial resolution at the nanometer scale.

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues X, 2012

RBC has been shown to possess shape memory subsequent to shear-induced shape transformation. Howe... more RBC has been shown to possess shape memory subsequent to shear-induced shape transformation. However, this property of RBC may not be generalized to all kinds of stresses. Here, we report our observation on the action of radiation pressure forces on RBC's shape memory using optical manipulation and quantitative phase microscopy (OMQPM). QPM, based on Mach-Zehnder interferrometry, allowed measurement of dynamic changes of shape of RBC in optical tweezers at different trapping laser powers. In high power near-infrared optical tweezers (>200mW), the RBC was found to deform significantly due to optical forces. Upon removal of the tweezers, hysteresis in recovering its original resting shape was observed. In very high power tweezers or long-term stretching events, shape memory was almost erased. This irreversibility of the deformation may be due to temperature rise or stress-induced phase transformation of lipids in RBC membrane.

Optics in the Life Sciences, 2011

We demonstrate the micromanipulation of RBC’s into a tapered fiber-optic trap for the transport i... more We demonstrate the micromanipulation of RBC’s into a tapered fiber-optic trap for the transport into and out of the optical tweezers trap in an orthogonal geometry.We are pursuing high-throughput transport analysis of the RBC's using this system.

Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VIII, 2012

Refractive index (RI) and its dispersion play a major role in interaction of electromagnetic wave... more Refractive index (RI) and its dispersion play a major role in interaction of electromagnetic wave with matter. Quantitative phase imaging (QPI) has proven to be a useful tool to estimate the RI from the sample-induced phase delay measurement at high spatio-temporal resolution. Here, we introduce near-infrared dispersive quantitative phase imaging (NIRD-QPI) of microscopic objects. The setup uses a new geometry for quantitative phase microscopy by use of spatial frequency filtering in Fourier plane. High resolution refractive index spectroscopic measurement over a range from 690 to 840nm in interval of 25nm is reported. This method could prove to be very useful for characterizing wide range of nano and biomaterials.

Optogenetics: Optical Methods for Cellular Control, 2013

Significant progress has been made in the application of optogenetic stimulation as a means to mo... more Significant progress has been made in the application of optogenetic stimulation as a means to modulate and control cellular functions within chemically-identical groups of cells. High resolution imaging can detect subtle morphological (shape/refractive index) changes in cells subsequent to optogenetic stimulation. Invasive topographical measurement methods such as mainstream AFM and other scanning probe techniques suffer from low temporal resolution and restricted field of view, resulting in reduced throughput, even though these methods exhibit high sensitivity to morphological changes. QPM, integrated with optogenetic stimulation incorporates a wide-field, label-free, non-invasive optical imaging technique for all optical stimulation and detection with high spatial and temporal resolution. We dynamically monitored phase of cells, sensitized with and without ChR2, using quantitative phase microscopy with and without light stimulation. The variation of phase in optogenetically stimulated cells (expressing ChR2) was found to be higher than that of the control cells. We report that our method could potentially evaluate effectiveness of various opsins and stimulation parameters including cellular function under different physiological surroundings via spatiallymodulated optogenetic stimulation and wide-field quantitative phase imaging.

Telecommunication Systems, 2008

This paper presents a proposal of a routing protocol to Wireless Sensor Networks, called SHRP (Si... more This paper presents a proposal of a routing protocol to Wireless Sensor Networks, called SHRP (Simple Hierarchical Routing Protocol), whose primary objective is to save battery energy. SHRP also provides both reliability and a load balance solution. As a novel proposal, it is a proactive protocol that chooses efficient routes, by selecting just the nodes that can contribute to extend the network lifetime. In addition this protocol is also able to inform to a central point about any possible disconnection caused by a reduction of battery power or a long interference period. The data defined by SHRP protocol can be aggregated during the sending and forwarding tasks. Redundant data are not sent, which contributes to energy saving. This protocol uses the IEEE 802.15.4 under of CC2420 radio chips and it has been implemented on TinyOS operation system.

Optics Letters, 2013

In quantitative phase imaging, a priori knowledge of either refractive index or physical thicknes... more In quantitative phase imaging, a priori knowledge of either refractive index or physical thickness is used to estimate the change in one of these parameters. Here, we report a method for decoupling geometric thickness from refractive index in quantitative phase microscopy.

Journal of Materials Science, 2007

... corrosion in flexible lines due to damage on external plastic layer, Technical Report PETROBR... more ... corrosion in flexible lines due to damage on external plastic layer, Technical Report PETROBRAS 45:6 6. Valadez-Gonzalez A, Veleva L (2004) Polym Degrad Stab 83:139 7. Rosa DS, Angelini JMG, Agnelli JAM, Mei LHI (2005 ... Qayyum MM, White JR (1985) J Mater Sci 20:2557 ...

Revista Colombia Médica

Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) ... more Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) de pacientes que fallecieron por la infección con VIH-SIDA. Metodología: Estudio retrospectivo de autopsias del 1 de enero de 2004 al 31 de diciembre de 2007 en un hospital público de tercer nivel en la ciudad de Bucaramanga, Santander. Resultados: El hallazgo neuropatológico más común en pacientes que fallecieron por la infección VIH-SIDA fue toxoplasmosis cerebral, 17 casos (28.3%) luego criptococosis cerebral, 7 casos (11.6%), tuberculosis del SNC, 3 casos (5%), encefalopatía por HIV, 2 casos (3.3%), meningitis piógena, un caso (1.6%) y hallazgos inespecíficos,2 casos (3.3%). No hubo lesiones neoplásicas, infecciones por citomegalovirus, herpes, histoplasmosis ni leucoencefalopatía multifocal progresiva (LMP) en ninguno de los casos. En el presente estudio se encontraron cambios en el SNC en 32 casos (53.1%), que, después del respiratorio (39-65%), fue el sistema más afectado por las complicaciones relacionadas con la enfermedad por VIH. La presencia de lesión directa (encefalitis por HIV) y al mismo tiempo infección oportunista se encontró sólo en un caso (1.6%). Conclusiones: En Bucaramanga las infecciones oportunistas fueron las complicaciones más frecuentes y graves a nivel del SNC en los enfermos con VIH-SIDA, de ellas la toxoplasmosis cerebral fue la que más comprometió el SNC de los pacientes con infección con VIH-SIDA, y se expresó morfológicamente como una meningoencefalitis necrosante, ubicada de manera preferencial en la región de los ganglios basales.

Applied Physics Letters, 2013

Quantitative phase microscopy (QPM) allows dynamic mapping of optical path length of microscopic ... more Quantitative phase microscopy (QPM) allows dynamic mapping of optical path length of microscopic samples with high temporal and axial resolution. However, decoupling of the geometric thickness from the refractive index in phase measurements is challenging. Here, we report use of optical tweezers combined with QPM for decoupling geometric thickness from the refractive index. This is demonstrated by orienting the microscopic sample (red blood cell) by optical tweezers and imaging the phase at various orientations. Since optical tweezers can orient wide variety of micro and nanoscopic objects, this integrated method can be employed to accurately determine their physical properties.

Applied Physics Letters, 2012

Hypotonic stimulation is known to cause morphological changes in cells and also leads to modulati... more Hypotonic stimulation is known to cause morphological changes in cells and also leads to modulation of cellular physiology. In order to evaluate the dynamics of cellular response to hypotonic stimulation, we utilized digital holographic microscopy for quantitative phase microscopy, achieved by a common-path interferometry geometry based on extraction of reference beam by spatial-filtering. Results from live cell investigations demonstrate the capability of this method for dynamic quantitative phase imaging. Further, wavelet and multi-fractal detrended fluctuation analysis revealed that the dynamic phase changes, in response to hypotonic stimulation, are multifractal in nature.

Colombia Medica, 1969

Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) ... more Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) de pacientes que fallecieron por la infección con VIH-SIDA. Metodología: Estudio retrospectivo de autopsias del 1 de enero de 2004 al 31 de diciembre de 2007 en un hospital público de tercer nivel en la ciudad de Bucaramanga, Santander. Resultados: El hallazgo neuropatológico más común en pacientes que fallecieron por la infección VIH-SIDA fue toxoplasmosis cerebral, 17 casos (28.3%) luego criptococosis cerebral, 7 casos (11.6%), tuberculosis del SNC, 3 casos (5%), encefalopatía por HIV, 2 casos (3.3%), meningitis piógena, un caso (1.6%) y hallazgos inespecíficos,2 casos (3.3%). No hubo lesiones neoplásicas, infecciones por citomegalovirus, herpes, histoplasmosis ni leucoencefalopatía multifocal progresiva (LMP) en ninguno de los casos. En el presente estudio se encontraron cambios en el SNC en 32 casos (53.1%), que, después del respiratorio (39-65%), fue el sistema más afectado por las complicaciones relacionadas con la enfermedad por VIH. La presencia de lesión directa (encefalitis por HIV) y al mismo tiempo infección oportunista se encontró sólo en un caso (1.6%). Conclusiones: En Bucaramanga las infecciones oportunistas fueron las complicaciones más frecuentes y graves a nivel del SNC en los enfermos con VIH-SIDA, de ellas la toxoplasmosis cerebral fue la que más comprometió el SNC de los pacientes con infección con VIH-SIDA, y se expresó morfológicamente como una meningoencefalitis necrosante, ubicada de manera preferencial en la región de los ganglios basales.

Optical Interactions with Tissue and Cells XXII, 2011

Red blood cells (RBC) possess unique viscoelastic characteristics which allow them to pass throug... more Red blood cells (RBC) possess unique viscoelastic characteristics which allow them to pass through capillaries narrower than their size. Measurement of viscoelastic property of cells (e.g. RBC) in low-force regime is of high significance as it represents conditions of membrane fluctuation in response to physiological conditions. Estimation of visco-elastic properties of RBC requires measurement of extent of deformation in RBC

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IX, 2011

While optical tweezers have been widely used for the manipulation and organization of microscopic... more While optical tweezers have been widely used for the manipulation and organization of microscopic objects in three dimensions, observing the manipulated objects along axial direction has been quite challenging. In order to visualize organization and orientation of objects along axial direction, we report development of a Digital holographic microscopy combined with optical tweezers. Digital holography is achieved by use of

Complex Light and Optical Forces V, 2011

High throughput analysis of trapped samples requires effective loading and unloading into the tra... more High throughput analysis of trapped samples requires effective loading and unloading into the trap in a microfluidic environment. We demonstrate development of a hybrid optical transport trap (HOTT) which combines a tapered fiberoptic 2D trap for transport of microscopic objects into and out of the optical tweezers trap in an orthogonal geometry. For small cone angle of the tip, the

Mammalian Biology, 2010

Habitat loss is one of the most important causes of biodiversity loss in South American temperate... more Habitat loss is one of the most important causes of biodiversity loss in South American temperate rainforests, where many endemic species exist. Among these is the monito del monte (Dromiciops gliroides), an arboreal marsupial with restricted distribution, and the only extant species of the order Microbiotheria. Current knowledge about monito del monte habitat use and its responses to human disturbances is scarce. To help fill this gap we investigated its habitat use and selection patterns in a fragmented landscape in southern Chile. Monito del monte individuals were abundant in a large and a small fragment, but rare or undetected in forest strips. Using telemetry data from 12 neighboring individuals in a large fragment and 2 individuals in a small fragment, we estimated their mean home range size of 1.6 ha70.6 (1SD). Monitos del monte had a spatial overlap among individuals of 5074%. Tracked individuals used old-and second-growth habitats as available, did not use the prairie habitats, and strongly avoided the scrublands. In the large fragment we estimated a relative population density of 2175 individuals/ha (mean71SD), whereas in the small fragment it was of 1976 individuals/ha. This is, to our knowledge, the first study of the spatial ecology of the monito del monte based on telemetry data, and evidence presented here could have conservation and planning implications, not only for the target species but also its habitat.

Communications in Computer and Information Science, 2008

This paper presents a new routing protocol to Wireless Sensor Networks called SHRP. This protocol... more This paper presents a new routing protocol to Wireless Sensor Networks called SHRP. This protocol has as principal goal the saving of energy and also provides reliability of data delivery. It is a novel proposal as it acts as a proactive protocol in respect to the choosing of routes, taking in consideration just nodes that can contribute to extend the network lifetime, that means, good battery status and good link quality. It also contributes to network management advising a central point about a possible disconnection of a node caused by low battery or large interference periods. Data messages can be added during the forwarding task and redundant sensing data are not sent, so it contributes again with the energy saving. We show that SHRP has a low time of convergence, which means that reacts quickly in case of topology changes, which is common in Wireless Sensor Networks, as the battery lifetime is low and the environment of wireless network uses to suffer from interferences and obstacles.

Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XVIII, 2011

Atomic Force Microscope (AFM) imaging, due to the scanning method of recording, requires signific... more Atomic Force Microscope (AFM) imaging, due to the scanning method of recording, requires significant recording time for examination of wide sample area. In contrast, digital holographic microscopy (DHM), owing to the wide-field method, allows recording of the hologram in very fast rate which could be numerically analyzed to reveal surface of the sample with axial resolution at the nanometer scale.

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues X, 2012

RBC has been shown to possess shape memory subsequent to shear-induced shape transformation. Howe... more RBC has been shown to possess shape memory subsequent to shear-induced shape transformation. However, this property of RBC may not be generalized to all kinds of stresses. Here, we report our observation on the action of radiation pressure forces on RBC's shape memory using optical manipulation and quantitative phase microscopy (OMQPM). QPM, based on Mach-Zehnder interferrometry, allowed measurement of dynamic changes of shape of RBC in optical tweezers at different trapping laser powers. In high power near-infrared optical tweezers (>200mW), the RBC was found to deform significantly due to optical forces. Upon removal of the tweezers, hysteresis in recovering its original resting shape was observed. In very high power tweezers or long-term stretching events, shape memory was almost erased. This irreversibility of the deformation may be due to temperature rise or stress-induced phase transformation of lipids in RBC membrane.

Optics in the Life Sciences, 2011

We demonstrate the micromanipulation of RBC’s into a tapered fiber-optic trap for the transport i... more We demonstrate the micromanipulation of RBC’s into a tapered fiber-optic trap for the transport into and out of the optical tweezers trap in an orthogonal geometry.We are pursuing high-throughput transport analysis of the RBC's using this system.

Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VIII, 2012

Refractive index (RI) and its dispersion play a major role in interaction of electromagnetic wave... more Refractive index (RI) and its dispersion play a major role in interaction of electromagnetic wave with matter. Quantitative phase imaging (QPI) has proven to be a useful tool to estimate the RI from the sample-induced phase delay measurement at high spatio-temporal resolution. Here, we introduce near-infrared dispersive quantitative phase imaging (NIRD-QPI) of microscopic objects. The setup uses a new geometry for quantitative phase microscopy by use of spatial frequency filtering in Fourier plane. High resolution refractive index spectroscopic measurement over a range from 690 to 840nm in interval of 25nm is reported. This method could prove to be very useful for characterizing wide range of nano and biomaterials.

Optogenetics: Optical Methods for Cellular Control, 2013

Significant progress has been made in the application of optogenetic stimulation as a means to mo... more Significant progress has been made in the application of optogenetic stimulation as a means to modulate and control cellular functions within chemically-identical groups of cells. High resolution imaging can detect subtle morphological (shape/refractive index) changes in cells subsequent to optogenetic stimulation. Invasive topographical measurement methods such as mainstream AFM and other scanning probe techniques suffer from low temporal resolution and restricted field of view, resulting in reduced throughput, even though these methods exhibit high sensitivity to morphological changes. QPM, integrated with optogenetic stimulation incorporates a wide-field, label-free, non-invasive optical imaging technique for all optical stimulation and detection with high spatial and temporal resolution. We dynamically monitored phase of cells, sensitized with and without ChR2, using quantitative phase microscopy with and without light stimulation. The variation of phase in optogenetically stimulated cells (expressing ChR2) was found to be higher than that of the control cells. We report that our method could potentially evaluate effectiveness of various opsins and stimulation parameters including cellular function under different physiological surroundings via spatiallymodulated optogenetic stimulation and wide-field quantitative phase imaging.

Telecommunication Systems, 2008

This paper presents a proposal of a routing protocol to Wireless Sensor Networks, called SHRP (Si... more This paper presents a proposal of a routing protocol to Wireless Sensor Networks, called SHRP (Simple Hierarchical Routing Protocol), whose primary objective is to save battery energy. SHRP also provides both reliability and a load balance solution. As a novel proposal, it is a proactive protocol that chooses efficient routes, by selecting just the nodes that can contribute to extend the network lifetime. In addition this protocol is also able to inform to a central point about any possible disconnection caused by a reduction of battery power or a long interference period. The data defined by SHRP protocol can be aggregated during the sending and forwarding tasks. Redundant data are not sent, which contributes to energy saving. This protocol uses the IEEE 802.15.4 under of CC2420 radio chips and it has been implemented on TinyOS operation system.

Optics Letters, 2013

In quantitative phase imaging, a priori knowledge of either refractive index or physical thicknes... more In quantitative phase imaging, a priori knowledge of either refractive index or physical thickness is used to estimate the change in one of these parameters. Here, we report a method for decoupling geometric thickness from refractive index in quantitative phase microscopy.

Journal of Materials Science, 2007

... corrosion in flexible lines due to damage on external plastic layer, Technical Report PETROBR... more ... corrosion in flexible lines due to damage on external plastic layer, Technical Report PETROBRAS 45:6 6. Valadez-Gonzalez A, Veleva L (2004) Polym Degrad Stab 83:139 7. Rosa DS, Angelini JMG, Agnelli JAM, Mei LHI (2005 ... Qayyum MM, White JR (1985) J Mater Sci 20:2557 ...

Revista Colombia Médica

Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) ... more Describir las alteraciones macro y microscópicas observadas en el sistema nervioso central (SNC) de pacientes que fallecieron por la infección con VIH-SIDA. Metodología: Estudio retrospectivo de autopsias del 1 de enero de 2004 al 31 de diciembre de 2007 en un hospital público de tercer nivel en la ciudad de Bucaramanga, Santander. Resultados: El hallazgo neuropatológico más común en pacientes que fallecieron por la infección VIH-SIDA fue toxoplasmosis cerebral, 17 casos (28.3%) luego criptococosis cerebral, 7 casos (11.6%), tuberculosis del SNC, 3 casos (5%), encefalopatía por HIV, 2 casos (3.3%), meningitis piógena, un caso (1.6%) y hallazgos inespecíficos,2 casos (3.3%). No hubo lesiones neoplásicas, infecciones por citomegalovirus, herpes, histoplasmosis ni leucoencefalopatía multifocal progresiva (LMP) en ninguno de los casos. En el presente estudio se encontraron cambios en el SNC en 32 casos (53.1%), que, después del respiratorio (39-65%), fue el sistema más afectado por las complicaciones relacionadas con la enfermedad por VIH. La presencia de lesión directa (encefalitis por HIV) y al mismo tiempo infección oportunista se encontró sólo en un caso (1.6%). Conclusiones: En Bucaramanga las infecciones oportunistas fueron las complicaciones más frecuentes y graves a nivel del SNC en los enfermos con VIH-SIDA, de ellas la toxoplasmosis cerebral fue la que más comprometió el SNC de los pacientes con infección con VIH-SIDA, y se expresó morfológicamente como una meningoencefalitis necrosante, ubicada de manera preferencial en la región de los ganglios basales.

Applied Physics Letters, 2013

Quantitative phase microscopy (QPM) allows dynamic mapping of optical path length of microscopic ... more Quantitative phase microscopy (QPM) allows dynamic mapping of optical path length of microscopic samples with high temporal and axial resolution. However, decoupling of the geometric thickness from the refractive index in phase measurements is challenging. Here, we report use of optical tweezers combined with QPM for decoupling geometric thickness from the refractive index. This is demonstrated by orienting the microscopic sample (red blood cell) by optical tweezers and imaging the phase at various orientations. Since optical tweezers can orient wide variety of micro and nanoscopic objects, this integrated method can be employed to accurately determine their physical properties.

Applied Physics Letters, 2012

Hypotonic stimulation is known to cause morphological changes in cells and also leads to modulati... more Hypotonic stimulation is known to cause morphological changes in cells and also leads to modulation of cellular physiology. In order to evaluate the dynamics of cellular response to hypotonic stimulation, we utilized digital holographic microscopy for quantitative phase microscopy, achieved by a common-path interferometry geometry based on extraction of reference beam by spatial-filtering. Results from live cell investigations demonstrate the capability of this method for dynamic quantitative phase imaging. Further, wavelet and multi-fractal detrended fluctuation analysis revealed that the dynamic phase changes, in response to hypotonic stimulation, are multifractal in nature.