Depletion of the neural precursor cell pool by glucocorticoids

OBJECTIVE: Glucocorticoids (GCs) are indicated for a number of conditions in obstetrics and perinatal medicine; however, the neurodevelopmental and long-term neurological consequences of early-life GC exposure are still largely unknown. Preclinical studies have demonstrated that GCs have a major influence on hippocampal cell turnover by inhibiting neurogenesis and stimulating apoptosis of mature neurons. Here we examined the fate of the limited pool of neural progenitor cells (NPCs) after GC administration during neonatal development; the impact of this treatment on hippocampal structure was also studied. METHODS: Phenotype-specific genetic and antigenic markers were used to identify cultured NPCs at various developmental stages; the survival of these cells was monitored after exposure to the synthetic glucocorticoid dexamethasone (DEX). In addition, the effects of neonatal DEX treatment on the neurogenic potential of the rat hippocampus were examined by monitoring the incorporation of bromodeoxyuridine and expression of Ki67 antigen at various postnatal ages. RESULTS: Multipotent nestin-expressing NPCs and Talpha1-tubulin-expressing immature neurons succumb to GC-induced apoptosis in primary hippocampal cultures. Neonatal GC treatment results in marked apoptosis among the proliferating population of cells in the dentate gyrus, depletes the NPC pool, and leads to significant and sustained reductions in the volume of the dentate gyrus. INTERPRETATION: Both NPCs and immature neurons in the hippocampus are sensitive to the proapoptotic actions of GCs. Depletion of the limited NPC pool during early life retards hippocampal growth, thus allowing predictions about the potential neurological and psychiatric consequences of neonatal GC exposure.S. Yu, Y Wu, and J Lu were supported by fellowships from the Max Planck Society. This study was partly supported by grants from the German Academic Exchange Service (to O.F.X.A. and N.S.) and the Portuguese Rectors' Conference, a grant from Gulbenkian Foundation (JG 0495 to N.S.), and an Integrated Project grant from the European Commission (Contract No. LSHM-CT-2005-01852 to O.F.X.A.)

Phonon assisted intersubband transitions in step quantum well structures

We evaluate effects of heterointerfaces on optical phonon modes and phonon assisted electron intersubband transition rates in step quantum well structures for intersubband lasers. Various phonon modes and electron–phonon interaction Hamiltonians, including the interface modes, confined longitudinal-optical modes, and half space modes in the quantum well structures are calculated based on the macroscopic dielectric continuum model and microscopic analysis. The transfer matrix method is used to calculate the interface modes. The intersubband transition rates due to electron–phonon scattering by these phonon modes are evaluated using Fermi’s golden rule, with the electron wave functions obtained by solving the Schrödinger equation for the heterostructures under investigation. Our results show that, compared with the transition rates in the same structures calculated using the bulk phonon modes and the bulk Fröhlich interaction Hamiltonian, the electron interface–phonon interactions give significantly larger transition rates up to an order of magnitude. Therefore, the effects of localized phonon modes, especially the interface modes, must be taken into consideration for optimal device design. © 1998 American Institute of Physics.  Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71224/2/JAPIAU-84-4-2155-1.pd

Transfer matrix method for interface optical-phonon modes in multiple-interface heterostructure systems

Interactions of carriers with interface optical phonons dominate over other carrier–phonon scatterings in narrow quantum-well structures. Herein, a transfer matrix method is used to establish a formalism for determining the dispersion relations, electrostatic potentials, and Fröhlich interaction Hamiltonians of the interface optical phonons for multiple-interface heterostructure systems within the framework of the macroscopic dielectric continuum model. This method facilitates systematic calculations for complex structures where the conventional method is very difficult to implement. Several specific cases are treated to illustrate the advantages of the general formalism. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70863/2/JAPIAU-82-7-3363-1.pd

Arduino based solar tracking system

This thesis proposes the dual axis solar tracker for optimum solar cell implementation using dc-dc boost converter controlled by fuzzy logic controller with the maximum power point tracking (MPPT) method. The objectives of this project are to track and optimize the maximum output power of the solar panel by designing and implementing the fuzzy logic controller using microcontroller as well as to regulate the output voltage of the solar panel using dc-dc boost converter. The system includes a solar panel, DC-DC boost converter, the fuzzy logic controller implemented on Arduino Uno for controlling on/off time of MOSFET of the boost converter, voltage divider and optocoupler circuit as a driver for MOSFET. Tracking and detecting the angle of the sun to locate the surface plate of solar cell at the position and the angle where it can get maximum amount of energy. The solar panel must have sensors that can detect the position of the sun and dc motors act as free moving neck to make it easier to move freely depending on the angle detected. The light dependent resistor (LDR) will be used as sun tracking. The photocell panel will detect the existing of sun and the surface plate of photocell panel will move horizontal and vertical axis depending on the value of LDR detected to follow the angular degree of sun in order to get maximum and best result of absorbing energy. Moreover, this project presents a fuzzy logic real time code in Arduino language for ATmega328 microcontroller at Arduino Uno board. The result obtained from the Arduino coding is the variation of duty cycle of PWM signal according to the voltage of solar panel. The final result obtained from dc-dc boost converter showed that the output voltage has been regulated. Overall, the designed system increases the efficiency of the solar panel based on experimental results

Dispersion retrieval from multi-level ultra-deep reactive-ion-etched microstructures for terahertz slow-wave circuits

A multi-level microstructure is proposed for terahertz slow-wave circuits, with dispersion relation retrieved by scattering parameter measurements. The measured return loss shows strong resonances above the cutoff with negligible phase shifts compared with finite element analysis. Splitting the circuit into multi levels enables a low aspect ratio configuration that alleviates the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles. The dispersion retrieved from the measurement, therefore, corresponds well to the theoretical estimation. The result provides a straightforward way to the precise determination of dispersions in terahertz vacuum electronics.</jats:p

Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche

In many tissues, homeostasis is maintained by physical contact between stem cells and an anatomically defined niche. However, how stem cell homeostasis is achieved in environments where cells are motile and dispersed among their progeny remains unknown. Using murine spermatogenesis as a model, we find that spermatogenic stem cell density is tightly regulated by the supply of fibroblast growth factors (FGFs) from lymphatic endothelial cells. We propose that stem cell homeostasis is achieved through competition for a limited supply of FGFs. We show that the quantitative dependence of stem cell density on FGF dosage, the biased localization of stem cells toward FGF sources, and stem cell dynamics during regeneration following injury can all be predicted and explained within the framework of a minimal theoretical model based on “mitogen competition.” We propose that this model provides a generic and robust mechanism to support stem cell homeostasis in open, or facultative, niche environments

High Electroluminescence of ZnS:Cu Phosphor with a CNT-Incorporated Dielectric Layer

High brightness was obtained for alternating current-driven inorganic ZnS:Cu powder electroluminescence (EL) devices by incorporating carbon nanotubes in a barium titanate (BaTiO3) based dielectric layer. The inorganic EL devices were consisted of four layers: a top electrode, a dielectric layer, an emitting layer, and an ITO layer which was pre-coated on the glass substrate. As an emitting material, ZnS:Cu power of particle size 9 µm (green emission) was mixed with the cyanoethyl pullulan polymer (CEP), as an organic binder, and the dimethyl formamide (DMF) organic solvent. The emitting solution was spin-coated on the ITO glass at the fixed speed of 1200 rpm. The BaTiO3 power were mixed with a CNT-CEP binder, which was also spin-coated on the emitting layer. In order to optimize the EL performance, the concentration of CNTs were varied by controlling the mixing ratio of CNTs—0, 0.0018, 0.0039, 0.0071, 0.011 and 0.014 wt%. Finally, a 500-nm-thick aluminum top electrode was thermally evaporated onto the dielectric layer. Up to 50% higher brightness was obtained for the CNT concentration of 0.011 wt%. The high brightness might be caused by the high dielectric constant of the CNT-incorporated BaTiO3 dielectric layer, thanks to the micro-capacitor effect. [Z. M. Dang et al., Small 12, 1688 (2016).] Roughly speaking, the higher concentration of the CNT yielded to the higher brightness, until a certain concentration, here, between 0.011 and 0.014 wt%. It implies that too high concentration of CNTs might lead to the formation of the unwanted percolation network of a leakage current within the dielectric layer. Finally, the role of the chlorine was investigated by inclusion of chlorobenzene into the CNT-containing dielectric layer. [J.-Y. Kim et al., Adv. Mater. 25, 2308 (2013).] Based on the above results, incorporation of CNTs within the dielectric layer enhanced the brightness (and the efficiency, possibly) of the ZnS:Cu-based EL device, which would help to extend the potential applications of EL devices.</jats:p

Dielectric Performance of Polymer Composites By Graphene Inclusion

Four series of polymer composites in which graphene and barium titanate (BaTiO3, BTO) were included for better dielectric performance—graphene oxide (GO) mixing with BTO, reduced graphene oxide (rGO) mixing with BTO, GO encapsulation of BTO, and rGO encapsulation of BTO. To find out the encapsulation of BTO in graphene, TEM, AFM, and Raman spectroscopy were performed on the dielectric samples. All graphene-included films showed 1.5~3 times higher values in the dielectric constants, regardless of the inclusion method, primarily due to the existence of graphene through the interfacial polarization of numerous micro-capacitors within the dielectric medium. On the while, the increase in the dielectric loss was nicely controlled, especially for encapsulation. The best performance came from the rGO encapsulated films, due to more conducting nature of rGO than GO, exhibiting a 300% higher dielectric constant (195 from 65) and a mere increase of 6% in the dielectric loss (0.033 from 0.031). It is the encapsulation by graphene that can minimize the percolation of graphene, i.e., the primary culprit of a poor dielectric loss. Thus, a smart mixing process with rGO, based on encapsulation and subsequent mixing, is desirable for high-performance dielectric composites, which can be easily applied to other two dimensional materials. Figure 1 <jats:p /