Radiation response of strained Si---SiO2 layered system

In the presented paper radiation effects in silicon-silicon dioxide systems in the presence of additional tensile and compressive stresses were investigated. These stresses were produced by placing additional layers of SiO₂ or Si₃N₄ on the back side of oxidized silicon wafers.The results obtained indicate that relaxation takes place in the oxide during irradiation and leads to the decrease of the compressive stress in the oxide film. Relaxation of strained bonds causes defect generation and the increase of the oxide charge density. This increase is larger for oxides with higher level of compressive stress. No significant changes of the density of surface states were observed since the additional coatings did not affect the strain gradient in the SiO₂.     

Novel organelles in primate retinal epithelium

We are investigating age-related changes in organelles in monkey retinal epithelium using transmission and analytic electron microscopy. We previously described a circular organelle in retinal epithelium with a diameter of about 0.5 μm. The organelle is unique in containing a single, round vacuole within an otherwise electron dense interior. We suggested that the organelle might be a melanosome with lysosomal properties. We now find that there are two similar organelles with such a single vacuole but which differ in their chemical composition, electron density, cell location and according to age.Epon embedded sections from the macular epithelium of seven monkeys, ranging from 1 to 35 years of age, were examined by transmission electron microscopy. A seven year old monkey was processed for analytic electron microscopy to determine the chemical composition of the organelles. The number and location of the organelles in the retinal epithelium were determined.The chemical composition of these two organelles was different. One of the organelles contained high mole fractions of oxygen and nitrogen and little phosphorous characteristic of melanin; the other had little oxygen and nitrogen and higher mole fractions of phosphorous uncharacteristic of melanin, but more common with lysosomal organelles. The latter had an electron dense rim around the vacuole, a less electron dense interior than the melanin containing organelle and also contained iron. The melanin containing organelle was more common in young monkeys and in the middle third of the cell. The organelle without melanin was more common in old monkeys and localized in the basal third of the cell.Two similarly vacuolated organelles, not identified before in retinal epithelium, differ in their chemical composition. One contains melanin; the other does not. The former is more common in young and the latter more common in old monkeys. This suggests reorganization and or degradation of melanin-containing organelles with age. These changes show how analytic electron microscopy can distinguish major ultra-structural differences in organelles when mere observation fails to do so easily.     

Radiation response of pseudo-MOS transistors fabricated in hardened fully-depleted SIMOX SOI wafers

The total dose radiation response of pseudo-MOS transistors fabricated in hardened and unhardened FD （fully-depleted） SIMOX （Separation by Implanted Oxygen） SOI （Silicon-on-insulator） wafers is presented. At 1 Mrad（Si） radiation dose, the threshold voltage shift of the pseudo-MOS transistor is reduced from -115.5 to -1.9 V by the hardening procedure. The centroid location of the net positive charge trapped in BOX, the hole-trap density and the hole capture fraction of BOX are also shown. The results suggest that hardened FD SIMOX SOI wafers can perform well in a radiation environment.     

Radiation response of pseudo-MOS transistors fabricated in hardened fully-depleted SIMOX SOI wafers

The total dose radiation response of pseudo-MOS transistors fabricated in hardened and unhardened FD (fully-depleted) SIMOX (Separation by Implanted Oxygen) SOI (Silicon-on-insulator) wafers is presented.At 1 Mrad(Si) radiation dose, the threshold voltage shift of the pseudo-MOS transistor is reduced from -115.5 to -1.9 V by the hardening procedure.The centroid location of the net positive charge trapped in BOX, the hole-trap density and the hole capture fraction of BOX are also shown.The results suggest that hardened FD SIMOX SOI wafers can perform well in a radiation environment.     

A gamma-tubulin antibody against a plant peptide sequence localises to cell division-specific microtubule arrays and organelles in plants

Gamma tubulin (gamma-tubulin) is involved in microtubule initiation in the eukaryotes. In animal cells it is localised to centrosomes and to other, non-centrosomal sites of microtubule initiation. In addition, cytoplasmic complexes containing gamma-tubulin (gamma-TuRCs; gamma-somes) have been described, which are multiprotein complexes involved in microtubule initiation. Most localisations of gamma-tubulin in plants have previously been achieved using an antibody directed towards a conserved peptide sequence found in animal cells, showing co-localisation with all microtubule arrays throughout the cell cycle. Because different antibodies may give various patterns of subcellular localisation, in the present study we raised a polyclonal antibody ('Hayley') to the plant peptide sequence EDFATQGGDRKDVFFY (bold letters indicate plant-specific amino acids) to further investigate the subcellular distribution in plants. Immunoblotting using wheat root tip protein extracts revealed a 58 kDagamma-tubulin-like peptide as has been described before. Immunofluorescence microscopy of wheat root-tip cells, however, revealed localisation of gamma-tubulin to a subset of mitotic microtubule arrays and the cytokinetic phragmoplast, but not to interphase cortical arrays or the preprophase band of microtubules. This lack of labelling may be caused by a restriction of antibody access during interphase, but more likely by a cell division-specific conformational change in the gamma-tubulin molecule. Our antibody also gave an organelle-like labelling, not described before, which may represent storage forms or precursors of gamma-tubulin, perhaps related to plastid-based microtubule initiation in hepatics and hornworts.     

Radiation response behaviour of Al codoped germano-silicate SM fiber at high radiation dose

Radiation response behaviour of Ge + Al doped SM fiber fabricated by the solution doping process has been studied at room temperature with respect to 1310 nm transmission wavelength under three different dose rates of 200, 400 and 600 Rad/min to compare with that of standard Er doped as well as Ge doped SM fibers. Their radiation sensitivity has been observed with variation of dose rates, transmission wavelength along with their recovery nature. Radiation response behaviour of Al doped SM fiber is found to be slightly non-linear in nature with very low dose rate dependency. No saturation level was found upto 13 Krad cumulative dose. Thermobleaching as well as photobleaching phenomena have also been studied. Gamma irradiated Al doped preform shows an absorption peak at around 300 nm due to generation of Al (E′) defect center and gets annihilated after thermobleaching process. Gamma irradiated Al doped SM fiber shows prominent photobleaching effect on their optical attenuation with respect to the 850 nm transmission wavelength. From ESR study resonance signals for Al³⁺ related radiation-induced defect centers are not clearly observed in this study. A very weak hyperfine pattern has been observed for gamma irradiated Al doped preform sample. The high radiation sensitivity along with linear response behaviour, low recovery and almost dose rate independence behaviour of the material system of Ge + Al codoped SM core optical fiber under gamma radiation shows their potential for application as fiber optic radiation sensor in comparison to the universal standard erbium doped SM fiber.     

Radiation dose response correlation between thermoluminescence and optically stimulated luminescence in quartz

The fast, linearly modulated optically stimulated luminescence (LM-OSL) component in quartz is the main dosimetric signal used for the dating applications of this material. Since the blue light stimulation (470 nm, 40 mW cm ${}^{?2}$) time needed to obtain the fast LM-OSL component is less than 50 s the electron trapping levels responsible for it are still highly populated. In this way an active radiation history is created which could play an important role in the dosimetric characteristics of the fast OSL signal. In the present work the dose response behavior of the fast OSL signal is investigated in quartz samples with an annealed radiation history and quartz samples possessing an artificial radiation history. A computerized curve de-convolution analysis of the LM-OSL curves for 50 s stimulation time showed that it consists of three individual OSL components. The faster component C₁ with peak maximum time around 5 s has a linear dose response in virgin samples, which turns to a slight superlinearity as a function of the artificial radiation history. On the other hand the component C₂ with peak maximum time at 12 s is slightly superlinear which turns into strong superlinearity as a function of artificial radiation history. Finally, component C₃ with peak maximum time at about 45 s is strongly superlinear for both virgin samples and as a function of artificial radiation history. The implications to practical application are discussed.     

Pacer cell response to periodic Zeitgebers

Almost all organisms show some kind of time periodicity in their behavior. In mammals, the neurons of the suprachiasmatic nucleus form a biological clock regulating the activity-inactivity cycle of the animal. The main question is how this clock is able to entrain to the natural 24 h light-dark cycle by which it is stimulated. Such a system is usually modeled as a collection of mutually coupled two-state (active-inactive) phase oscillators with an external stimulus (Zeitgeber). In this article however, we investigate the entrainment of a single pacer cell to the ensemble of other pacer cells. Moreover the stimulus of the ensemble is taken to be periodic. The pacer cell interacts with its environment by phase delay at the end of its activity interval and phase advance at the end of its inactivity interval. We develop a mathematical model for this system, naturally leading to a circle map depending on parameters like the intrinsic period and phase delay and advance. The existence of resonance tongues in a circle map shows that an individual pacer cell is able to synchronize with the ensemble. We furthermore show how the parameters in the model can be related to biological observable quantities. Finally we give several directions of further research.     

Osteoblastic cell response on magnesium-incorporated apatite coatings

Magnesium is one of the most important bivalent ions associated with biological apatite. A series of magnesium-substituted calcium apatite coatings (Ca_10−xMg_x)(PO₄)₆(OH)₂, where x = 0, 0.50, 1.00, 1.50 and 2.00, are synthesized onto Ti6Al4V substrate by sol-gel dip-coating method to determine how magnesium influences the synthesis and the resulting structural and biological properties. X-ray diffraction (XRD) analysis shows that the incorporation of magnesium helps formation of Mg-containing β-TCP (β-TCMP) phase. X-ray photoelectron spectroscopy (XPS) is used to study the chemical composition and the results show that the apatite structure can only host magnesium less than ∼2.4 wt.% beyond which magnesium aggregates on the surfaces. The incorporation of magnesium slows down the dissolution of Ca²⁺ from the coating. The in vitro behavior of the coatings is evaluated with human osteosarcoma MG63 cells for cell morphology and proliferation. Similar cell morphologies are observed on all coatings. The cell proliferation results show that the incorporation of magnesium up to x = 2 has no adverse effect on cell growth.     

Apodized phase contrast microscopy for bright high contrast reveals motion of organelles

Optical Review - We have developed a high magnification objective lens performed with apodized phase contrast microscopy for bright high contrast, aiming to image finer intact intracellular...     

The evidence of Tobacco rattle virus impact on host plant organelles ultrastructure

Tobraviruses, like other (+) stranded RNA viruses of plants, replicate their genome in cytoplasm and use such usual membranous structures like endoplasmic reticulum. Based on the ultrastructural examination of Tobacco rattle virus (TRV)-infected potato and tobacco leaf tissues, in this work we provide evidence of the participation of not only the membranous and vesicular ER structures but also other cell organelles during the viral infection cycle. Non-capsidated TRV PSG particles (potato isolate from the Netherlands) (long and short forms) were observed inside the nucleus while the presence of TRV capsid protein (CP) was detected in the nucleus caryolymph and within the nucleolus area. Both capsidated and non-capsidated viral particles were localized inside the strongly disorganized chloroplasts and mitochondria. The electron-dense TRV particles were connected with vesicular structures of mitochondria as well as with chloroplasts in both potato and tobacco tissues. At 15–30 days after infection, vesicles filled with TRV short particles were visible in mitochondria revealing the expanded cristae structures. Immunodetection analysis revealed the TRV PSG CP epitope inside chloroplast with disorganized thylakoids structure as well as in mitochondria of different tobacco and potato tissues. The ultrastructural analysis demonstrated high dynamics of the main cell organelles during the TRV PSG–Solanaceous plants interactions. Moreover, our results suggest a relationship between organelle changes and different stages of virus infection cycle and/or particle formation.     

Radiation reaction

I solve Maxwell's equation for a current produced by a classical, point electron. My solution, which represents the self electromagnetic field of the electron, can be found along the electron trajectory, where the conventional retarded-time solution is singular. The solution is in the form of an integral over all spectral frequencies of the field and has an Ehrenfest correspondence with the operator field of quantum electrodynamics (QED). Use of the field in the equation of motion for a harmonically-bound electron leads to an equation having the same form as the Schrödinger equation for a two-level atom interacting with the QED vacuum field.     

Radiation magnetization

Radiation magnetization represents a new electron induction effect within ferrites resulting in real permanent magnetization, dynamically induced and detected by means of microwaves Strahlungsmagnetisierung kennzeichnet einen neuen Effekt der Elektronenanregung (electron induction) innerhalb von Ferriten. Strahlungsmagnetisierung ist eine reelle permanente Magnetisierung, die von Mikrowellen dynamisch induziert und gemessen wird.     

Relaxation dynamics and frequency response of a noisy cell signaling network

We investigate the dynamics of cell signaling using an experimentally based Boolean model of the human fibroblast signal transduction network. We determine via systematic numerical simulations the relaxation dynamics of the network in response to a constant set of inputs, both in the absence and in the presence of environmental fluctuations. We then study the network's response to periodically modulated signals, uncovering different types of behaviors for different pairs of driven input and output nodes. The phenomena observed include low-pass, high-pass, and band-pass filtering of the input modulations, among other nontrivial responses, at frequencies around the relaxation frequency of the network. The results reveal that the dynamic response to the external modulation of biologically realistic signaling networks is versatile and robust to noise.     

Radiation pressure

Formulae for the radiation pressure of electromagnetic and of sound waves are reviewed. The pressure on an obstacle in the path of the waves can be calculated from the momenta of the incident and scattered trains, and it is now well established that any train of waves of intensity J propagated with speed v has momentum J/v ² per unit volume. A general proof of this result is proposed, independent of the nature of the waves.     

Small-signal ac response of an electrolytic cell with recombining space charge

A simple model to evaluate the impedance of a cell in the presence of the generation and recombination of charges is proposed. The analysis is performed by considering a typical asymmetric cell having one electrode perfectly blocking and the other electrode perfectly transparent. The dependence of the impedance of the cell, in the shape of a slab, on the recombination coefficient is investigated. We obtain approximated expressions for the impedance of the cell valid in the low and high frequency regions. The frequencies defining the regions where approximated expressions hold are deduced by means of the asymptotic expansions for the real and imaginary parts of the electrical impedance of the cell.     

Measurement of Radiation Dose Level of Synchrotron Radiation Experimental Hall of BEPC

This paper describes the radiation source and its characteristics of the Synchrotron Radiation Experimental Hall of BEPC,the radiation measuring method and measured results.It has been found that the radiation dose level of the Synchrotron Radiation Experimental Halls is closely correlative with the relative location of the Experimental Halls to the injection points of the electron and positron beams,the thicknesses of the shielding walls,the times and efficiencies of the beam injections.