Midinfrared semiconductor optical metamaterials

We report on a novel class of semiconductor metamaterials that employ a strongly anisotropic dielectric function to achieve negative refraction in the midinfrared region of the spectrum, ~8.5–13 μm. We present two types of metamaterials, layered highly doped/undoped heterostructures and quantum well superlattices that are highly anisotropic. Contrary to other optical metamaterials these heterostructure systems are optically thick (up to 20 μm thick), planar, and require no additional fabrication steps beyond the initial growth. Using transmission and reflection measurements and modeling of the highly doped heterostructures, we demonstrate that these materials exhibit negative refraction. For the highly doped quantum well superlattices, we demonstrate anomalous reflection due to the strong anisotropy of the material but a determination of the sign of refraction is still difficult. This new class of semiconductor metamaterials has great potential for waveguiding and imaging applications in the long-wave infrared

Sunlight-Exposed Biofilm Microbial Communities Are Naturally Resistant to Chernobyl Ionizing-Radiation Levels

BACKGROUND: The Chernobyl accident represents a long-term experiment on the effects of exposure to ionizing radiation at the ecosystem level. Though studies of these effects on plants and animals are abundant, the study of how Chernobyl radiation levels affect prokaryotic and eukaryotic microbial communities is practically non-existent, except for a few reports on human pathogens or soil microorganisms. Environments enduring extreme desiccation and UV radiation, such as sunlight exposed biofilms could in principle select for organisms highly resistant to ionizing radiation as well. METHODOLOGY/PRINCIPAL FINDINGS: To test this hypothesis, we explored the diversity of microorganisms belonging to the three domains of life by cultivation-independent approaches in biofilms developing on concrete walls or pillars in the Chernobyl area exposed to different levels of radiation, and we compared them with a similar biofilm from a non-irradiated site in Northern Ireland. Actinobacteria, Alphaproteobacteria, Bacteroidetes, Acidobacteria and Deinococcales were the most consistently detected bacterial groups, whereas green algae (Chlorophyta) and ascomycete fungi (Ascomycota) dominated within the eukaryotes. Close relatives to the most radio-resistant organisms known, including Rubrobacter species, Deinococcales and melanized ascomycete fungi were always detected. The diversity of bacteria and eukaryotes found in the most highly irradiated samples was comparable to that of less irradiated Chernobyl sites and Northern Ireland. However, the study of mutation frequencies in non-coding ITS regions versus SSU rRNA genes in members of a same actinobacterial operational taxonomic unit (OTU) present in Chernobyl samples and Northern Ireland showed a positive correlation between increased radiation and mutation rates. CONCLUSIONS/SIGNIFICANCE: Our results show that biofilm microbial communities in the most irradiated samples are comparable to non-irradiated samples in terms of general diversity patterns, despite increased mutation levels at the single-OTU level. Therefore, biofilm communities growing in sunlight exposed substrates are capable of coping with increased mutation rates and appear pre-adapted to levels of ionizing radiation in Chernobyl due to their natural adaptation to periodical desiccation and ambient UV radiation

Differential effects of angiotensin II on cardiorespiratory reflexes mediated by nucleus tractus solitarii – a microinjection study in the rat

The effect of microinjecting angiotensin II (ANGII) into the nucleus of the solitary tract (NTS) on both baroreceptor and peripheral chemoreceptor reflexes was compared.Experiments were performed in a working heart-brainstem preparation of rat. Baroreceptors were stimulated by raising perfusion pressure and chemoreceptors were activated with aortic injections of sodium cyanide (0·025%, 25–75 μl). Reflex changes in phrenic nerve activity and heart rate were measured after bilateral NTS microinjection (50 nl) of ANGII (0·5–5000 fmol).NTS microinjection of 5 fmol ANGII elicited a transient (28·2 ± 6 s; mean ± s.e.m.) bradycardia (-18 ± 3 beats min−1), and decreased phrenic nerve activity cycle length and amplitude (P < 0·05). At higher doses of ANGII a similar respiratory response was seen but heart rate changes were inconsistent.The baroreceptor reflex bradycardia was depressed significantly by NTS microinjections of ANGII (5–5000 fmol) in a dose-dependent manner with the reflex gain decreasing from 1·7 ± 0·16 to 0·66 ± 0·1 beats min−1 mmHg−1 (P < 0·01) at 5000 fmol. Although the chemoreceptor reflex bradycardia was depressed at a low dose of ANGII (5 fmol), all higher doses (50–5000 fmol) produced a dose-dependent potentiation of the reflex bradycardia (maximally +64 ± 8%). The respiratory component was unaffected. The effects of ANGII on both reflexes were blocked by an ANGII type 1 (AT1) receptor antagonist, losartan (20 μM).The potentiating action of ANGII on the chemoreceptor reflex cardiac response was abolished by a neurokinin type 1 (NK1) receptor blocker (CP-99,994, 5 μM) but this had no effect on the baroreceptor reflex.AT1 receptors in the NTS can depress the baroreceptor reflex bradycardia which is independent of NK1 receptors. The ANGII effect on the cardiac component of the chemoreceptor reflex is bi-directional being inhibited at low concentrations and potentiated at higher concentrations; the latter involves NK1 receptors and presumably results from release of substance P

Differential effects of angiotensin II in the nucleus tractus solitarii of the rat – plausible neuronal mechanisms

Cellular mechanisms of the actions of angiotensin II (ANGII) within the nucleus of the solitary tract (NTS) were studied using rat brain slices in 78 neurones recorded in the whole-cell configuration. Twenty-nine per cent of cells had an on-going activity and with only one exception these cells responded to tractus solitarii (TS) stimulation with a monophasic excitatory postsynaptic potential (EPSP). In approximately half of the silent cells, TS stimulation evoked an EPSP-inhibitory postsynaptic potential (IPSP) complex.The ANGII (200 or 1000 nM) effect on TS-evoked EPSPs depended on the cell subpopulation. In cells with on-going activity, ANGII (1000 nM) increased evoked EPSP amplitude by +70 ± 13% (means ± s.e.m., n = 5) but reduced it (200 and 1000 nM) in silent cells where both evoked EPSPs and IPSPs were present. ANGII either increased TS-evoked IPSP conductances in cells where they were detectable or revealed an evoked IPSP (200 nM ANGII: IPSP conductance increased from 70 ± 29 to 241 ± 34 pS; n = 11). All ANGII effects were prevented by the ANGII type 1 (AT1) receptor blocker losartan. Since 200 nM ANGII did not increase responses to iontophoretically applied GABA, the effect of ANGII on TS-evoked IPSPs may occur presynaptically.The neurokinin type 1 (NK1) receptor antagonist CP-99,994 (5 μM) blocked the ANGII-induced increase in EPSPs but had no effect on TS-evoked IPSP potentiation by ANGII.Thus, ANGII can potentiate both inhibitory and excitatory synaptic transmission within different subpopulations of NTS neurones. Potentiation of evoked EPSPs, but not of IPSPs, involves activation of NK1 receptors. The balance of these actions of ANGII could be reflex specific: for the baroreflex circuitry the inhibitory action might predominate while the peripheral chemoreceptor reflex may be facilitated due to enhanced excitatory transmission