Blueshift and Narrowing of Localized Surface Plasmon Resonance of Silver Nanoparticles Exposed to Plasma

We have demonstrated that plasma treatments of silver nanoparticles bring about blueshift and narrowing in their localized surface plasmon resonance. Surface-enhanced Raman scattering analysis revealed that hydrocarbons adsorbed on silver surfaces were removed effectively by plasma exposure. It was found that the decrease in Raman line intensity for hydrocarbons was correlated well with the blueshift. Our findings indicate that one of the most important factors for remarkable differences in plasmon resonance wavelengths and line widths reported for the silver nanoparticles supported on substrates between most of the experimental data and calculations by Mie’s theory is due to the impurity adsorption on silver surfaces.     

Negative refraction angular characterization in one-dimensional photonic crystals

Background

Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs.

Methodology/Principal Findings

By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell''s law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone.

Conclusions/Significance

Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.     

A comparison of resonance tuning with positive versus negative sensory feedback

We used a computational model of rhythmic movement to analyze how the connectivity of sensory feedback affects the tuning of a closed-loop neuromechanical system to the mechanical resonant frequency (ω_r). Our model includes a Matsuoka half-center oscillator for a central pattern generator (CPG) and a linear, one-degree-of-freedom system for a mechanical component. Using both an open-loop frequency response analysis and closed-loop simulations, we compared resonance tuning with four different feedback configurations as the mechanical resonant frequency, feedback gain, and mechanical damping varied. The feedback configurations consisted of two negative and two positive feedback connectivity schemes. We found that with negative feedback, resonance tuning predominantly occurred when ω_r was higher than the CPG’s endogenous frequency (ω_CPG). In contrast, with the two positive feedback configurations, resonance tuning only occurred if ω_r was lower than ω_CPG. Moreover, the differences in resonance tuning between the two positive (negative) feedback configurations increased with increasing feedback gain and with decreasing mechanical damping. Our results indicate that resonance tuning can be achieved with positive feedback. Furthermore, we have shown that the feedback configuration affects the parameter space over which the endogenous frequency of the CPG or resonant frequency the mechanical dynamics dominates the frequency of a rhythmic movement.     

Factors affecting large-scale distribution of the Bonelli’s eagle <Emphasis Type="Italic">Aquila fasciata</Emphasis> in Spain

We analyzed the environmental determinants of the regional distribution of Bonelli’s eagle (Aquila fasciata) in Spain (ca. 500,000 km²), taking into account its frequency of occurrence on UTM blocks of 50 × 50 km. We found that the distribution pattern of Bonelli’s eagle was a highly predictable phenomenon based on climate, vegetation and interspecific relationships. The proportion of sunny, anticyclonic days, per year (i.e., high levels of solar radiation) was the main environmental predictor explaining the distribution and abundance pattern of the Bonelli’s eagle. Sparse plant formations (mainly shrublands) had also a positive effect, while altitude, agricultural land and deciduous forests had a negative influence. The relative abundance of one of its main preys, the Red Partridge (Alectoris rufa), favored the probability of occurrence of Bonelli’s eagle, but only in the less sunny areas located in the north of Spain. The relative abundance of its main competitor, the Golden eagle (Aquila chrysaetos), was slightly but positively correlated with both the distribution and the abundance of the Bonelli’s eagle in the Spanish portion of the Iberian Peninsula, probably due to similarities in their habitat preferences. Finally, we did not find further regional effects of the variables describing the degree of human pressure (density of roads, urban cover, and length of power lines).     

Defining a Superlens Operating Regime for Imaging Fluorescent Molecules

It has been shown that thin metal-based films can at certain frequencies act as planar near-field lenses for certain polarization components. A desirable property of such “lenses” is that they can also enhance and focus some large transverse spatial frequency components which contain sub-diffraction limit details. Over the last decade there has been much work in optimizing designs to reduce effects (such as material losses and surface roughness) that are detrimental to image reconstruction. One design that can reduce some of these undesirable effects, and which has received a fair amount of attention recently, is the stacked metal-dielectric superlens. Here we theoretically explore the imaging ability of such a design for the specific purpose of imaging a fluorescent dye (the common bio-marker GFP) in the vicinity of the superlens surface. Our calculations take into consideration the interaction (damping) of an oscillating electric dipole with the metallic layers in the superlens. We also assume a Gaussian frequency distribution spectrum for the dipole. We treat the metallic-alloy and dielectric-alloy layers separately using an appropriate effective medium theory. The transmission properties are evaluated via Transfer matrix (-matrix) calculations that were performed in the MatLab and MathCad environments. Our study shows that it is in principle possible to image fluorescent molecules using a simple bilayer planar superlens. We find that optimal parameters for such a superlens occur when the peak dipole emission-frequency is slightly offset from the Surface Plasmon resonance frequency of the metal-dielectric interfaces. The best resolution is obtained when the fluorescent molecules are not too close ( nm) or too far ( nm) from the superlens surface. The realization and application of a superlens with the specified design is possible using current nanofabrication techniques. When combined with e.g. a sub-wavelength grating structure (such as in the far-field superlens design previously proposed [1]) or a fast near-field scanning probe, it could provide a means for fast fluorescent imaging with sub-diffraction limit resolution.     

Negative and Positive Impact of Roughness and Loss on Subwavelength Imaging for Superlens Structures

We study on the negative and positive effect of surface roughness and loss coefficient on subwavelength imaging of the superlens structure. It has been found that even though surface roughness enables more transmission of high spatial frequency components, the random interferential noise between neighborhood images becomes more severe with increasing distortion. We show that additional loss is able to restrain the interferential noise caused by random roughness while preserving the imaging integrity. The results with practical parameters prove that the mean contrast and uniformity are improved by adding adequate loss on rough surface. Moreover, other two situations are further studied: (a) a single superlens with roughness on different interfaces and (b) a multilayered alternated metal–dielectric superlens with roughness on each surface. We found that the roughness on the imaging surface (metal–photoresist interface) plays a major role in determining the superlens imaging. The multilayer superlens is able to enhance the subwavelength imaging with fractionalized thinner films. But with the further fractionizing layers, the multilayer becomes more vulnerable to the roughness due to the multiple mixing and distorting. We still prove that additional loss is able to improve the performance in both situations.     

Analytical Approach to the Prism Coupling Problem in the Kretschmann Configuration

Prism coupling in the Kretschmann configuration is a well-known method for excitation of surface plasmon polaritons (SPP’s) in a metal film bounded from one side by a prism and from the other side by air. The analysis of the reflectance in the upper medium (prism) is based on the well-known Fresnel’s formula. Due to the fact that this formula cannot be inverted directly to give the complex dielectric permittivity and the thickness of the metal film from measured values of the reflectance at three or more different angles of incidence, an additional analysis is needed. Here, such an analysis is presented. The special case of illumination with He–Ne laser (λ = 632.8 nm) of silver film bounded by air is considered. A new asymptotic formula for the Lorentz dip is derived. Our experimental data for silver film are reported too.     

Qualitative analysis of the all-cause black-white mortality crossover

To date, despite decades of investigations and the relative abundance of mortality data, our understanding of the phenomenon of ‘mortality crossover’ remains inadequate. We propose a methodology for transforming mortality data from the ‘age-domain’ to the ‘time-domain’. We then introduce a model of selection partially offset by mobility, to simulate the dynamics of vulnerability in a population cohort that is heterogeneous in health and death. Using our model of vulnerability simulating the dynamics of mortality in the time-domain, we compare the mortality experience of the Black and White populations of the United States, identify the significance of selection and mobility as potential factors producing the crossover phenomenon, and make diagnostic use of them.     

Fabrication and characterization of silver nanoparticle and its potential antibacterial activity

In the present research silver nanoparticle was fabricated by chemical reduction of silver salt (Silver nitrate, AgNO₃) solution. Sodium citrate was used as a reducer. The formation of silver nanoparticle was observed visually by color change (greenish yellow). The surface plasmon resonance peak in absorption spectra of silver nanoparticle showed an absorption maximum at 420 nm in UV-VIS spectrometry. The X-ray diffraction pattern showed the presence of sharp reflections at 111, 200, 220, and 311. This would indicate the presence of silver nanoparticle. The scanning electron micrograph revealed that the average size of silver nanoparticle was 21.22 ± 5.17 nm. Silver nanoparticle exhibited better antimicrobial activity against Staphylococcus aureus than the other bacterial pathogens. The correlation coefficient between silver nanoparticles and selected bacterial pathogens revealed that there is a strong negative correlation with Escherichia coli, S. aureus and Klebsiella pneumonia (r = −0.975, −0.993, and −0.998, respectively).     

Residents’ attitudes toward three protected areas in southwestern Nepal

Understanding people’s beliefs and attitudes toward protected areas is a key factor in developing successful management plans to conserve those areas over the long-term. Yet, most of the emphasis in understanding people’s perceptions has been on the conflicts that exist between people and protected areas, such as loss of traditional extraction access or damage by wildlife to crops and livestock. This study addresses the need to explore people’s attitudes toward protected areas in a way that allows them to define and describe the values they hold toward the areas and the relevant issues and concepts. Three contrasting protected areas in the southwestern region of Nepal were chosen for this study to gain a broad representation of the values people hold toward different types of protected areas. Three themes emerged that describe the positive perceptions residents have: recreation/esthetics, environmental preservation, and economic benefits. Four themes emerged that describe the negative perceptions: negative economic impacts, belief that benefits are for the government or foreigners, fear of wildlife, and negative interactions with park guards. People’s perceptions are affected by different aspects of the areas, including the size of the area and people’s access to them, management objectives, history, and tourism. The diversity of these perceptions suggests that conservation strategies should recognize both positive and negative perceptions and work to foster and integrate diverse values in order to more accurately reflect the reality and complexity of people’s lives.     

Binocular fusion in Panum’s limiting case of stereopsis obeys the uniqueness constraint

In the information processing procedure of stereo vision, the uniqueness constraint has been used as one of the constraints to solve the “correspondence problem”. While the uniqueness constraint is valid in most cases, whether it is still valid in some particular stimulus configuration (such as Panum’s limiting case) has been a problem of widespread debate for a long time. To investigate the problem, we adopted the Panum’s limiting case as its basic stimulus configuration, and delved into the phenomenon of binocular fusion from two distinct aspects: visual direction and orientation disparity. The results show that in Panum’s limiting case binocular fusion does not comply with the rules governing regular binocular fusion as far as visual direction and orientation disparity are concerned. This indicates that double fusion does not happen in Panum’s limiting case and that the uniqueness constraint is still valid.     

Binocular fusion in Panum’s limiting case of stereopsis obeys the uniqueness constraint

In the information processing procedure of stereo vision, the uniqueness constraint has been used as one of the constraints to solve the “correspondence problem”. While the uniqueness constraint is valid in most cases, whether it is still valid in some particular stimulus configuration (such as Panum’s limiting case) has been a problem of widespread debate for a long time. To investigate the problem, we adopted the Panum’s limiting case as its basic stimulus configuration, and delved into the phenomenon of binocular fusion from two distinct aspects: visual direction and orientation disparity. The results show that in Panum’s limiting case binocular fusion does not comply with the rules governing regular binocular fusion as far as visual direction and orientation disparity are concerned. This indicates that double fusion does not happen in Panum’s limiting case and that the uniqueness constraint is still valid.     

Atypical Micromorphology and Uncommon Location of Cryptococcosis: A Histopathologic Study Using Special Histochemical Techniques (One Case Report)

Here we report an unusual case of disseminated cryptococcosis in a patient with AIDS. Although typical Cryptococcus neoformans micromorphology was observed in tongue biopsy, cervical lymph node examination revealed atypical histopathologic findings. These included pseudohyphae, chains of budding yeasts and structures resembling germ tubes. Cryptococcus neoformans infection in supraclavicular lymph nodes was also confirmed by culture. The importance of using special histochemical techniques—Mayer’s mucicarmine stain for mucicarminophilic capsule and Grocott’s silver stain—in the diagnosis of cryptococcosis is reinforced.     

Capuchin monkeys (<Emphasis Type="Italic">Cebus apella</Emphasis>) modify their own behaviors according to a conspecific’s emotional expressions

Understanding conspecifics’ emotional states is important for managing social interactions. We examined whether capuchin monkeys modify their own behaviors in response to a conspecific’s emotional expressions. Six monkeys saw a demonstrator monkey responding emotionally to an object in a container; the subject monkeys could not see the object. The subjects reached for the container more frequently when the demonstrator showed an emotionally positive expression than when she showed an emotionally neutral or negative expression. This is the first report that New World monkeys are sensitive to the emotional valence of conspecifics’ emotional expressions. The finding is consistent with the hypothesis that monkeys can recognize emotional meanings in others’ expressions, an ability previously attributed only to humans and great apes.     

Gould’s replay revisited

This paper develops a critical response to John Beatty’s recent (2006) engagement with Stephen Jay Gould’s claim that evolutionary history is contingent. Beatty identifies two senses of contingency in Gould’s work: an unpredictability sense and a causal dependence sense. He denies that Gould associates contingency with stochastic phenomena, such as drift. In reply to Beatty, this paper develops two main claims. The first is an interpretive claim: Gould really thinks of contingency has having to do with stochastic effects at the level of macroevolution, and in particular with unbiased species sorting. This notion of contingency as macro-level stochasticity incorporates both the causal dependence and the unpredictability senses of contingency. The second claim is more substantive: Recent attempts by other scientists to put Gould’s claim to the test fail to engage with the hypothesis that species sorting sometimes resembles a lottery. Gould’s claim that random sorting is a significant macroevolutionary phenomenon remains an intriguing and largely untested live hypothesis about evolution.     

Where does heteroclisis come from? Evidence from Romanian dialects

This study examines some cases of heteroclisis in the history of Romanian dialects, and concludes that the data call for a reconsideration of Stump’s distinction (Language 82:279–322, 2006) between ‘cloven’ heteroclisis, where the intraparadigmatic ‘split’ is aligned with some morphosyntactic feature distinction, and ‘fractured’ heteroclisis, where this is not the case and the pattern of heteroclisis is purely morphological. Stump’s account creates the impression that the ‘cloven’ variety is universally predominant, and that the ‘fractured’ variety tends to follow very closely the available ‘cloven’ patterns of the language. I shall suggest, instead, that the ‘fractured-only’ situation may in fact underlie heteroclisis cross-linguistically, the phenomenon being in general sensitive not directly to morphosyntactic content, but rather to characteristic, and often purely ‘morphomic’, patterns of stem-allomorphy. Research for this paper was undertaken as part of the Arts and Humantities Research Council-funded project Autonomous Morphology in Diachrony: comparative evidence from the Romance Languages, currently being conducted at Oxford University.     

Recurring Plankton Bloom Dynamics Modeled via Toxin-Producing Phytoplankton

A simple nutrient–phytoplankton model is proposed and analyzed in the presence of toxic chemicals released by toxin-producing phytoplankton (TPP) to understand the dynamics of seasonally recurring bloom phenomena. We observe that the presence of toxic chemicals helps to explain the bloom phenomenon. We have further studied our proposed system by varying the toxin liberation rate. Our model displays a wide range of dynamical behaviours, from simple cyclical blooms to irregular chaotic blooms. We also observe skipping phenomenon. The effect of toxic chemicals released by TPP cannot, thus, be ignored in ‘bottom-up’ models. J. Chattopadhyay is supported by the Ministry of Foreign Affairs Indo-Italian program of cooperation in Science and Technology, “Biomedical Sciences”. S. Chatterjee is supported by Ministero dell’Istruzione, dell’Università e della Ricerca, Bando per borse a favore di giovani ricercatori indiani. S. Chakraborty is supported by the Council of Scientific and Industrial Research, Human Resource Development Group, New Delhi.     

Discovery of “punch-through” or membrane electrical breakdown and electroporation

As part of a detailed study in Alex Hope’s laboratory of the V–I characteristics of the membrane of the giant cells of Chara corallina, it was discovered that at a well defined potential difference of around 500 mV (depending on the temperature), the cell membrane undergoes a reversible electrical breakdown. The author coined the word “punchthrough” to describe this electrical breakdown phenomenon. Detailed studies followed on the nature of this electrical breakdown phenomenon, in various cells, aimed at elucidating the physical mechanism(s) involved. The applications and the significance of the phenomenon that were subsequently developed in later years were not foreseen at that time. Electrical breakdown/electroporation is now a commonplace procedure and has entered into the mainstream biological vocabulary. Here we trace its humble beginnings to experiments carried out in Alex Hope’s laboratory and review briefly some of the aspects of this phenomenon and its applications that were developed much later by others as well as the author. The discovery of membrane electrical breakdown described below took whilst the author was his student of Alex Hope but whilst Alex was away on sabbatical leave in the UK. Because this occurred in his absence, Alex Hope elected to not put his name on the paper that described the discovery in 1965.     

Luminescence Study of Silver Nanoparticles Obtained by Annealed Ionic Exchange Silicate Glasses

The photoluminescence of silver nanoparticles glasses obtained by ionic exchange and annealing is investigated for various ionic exchange times. These glasses are prepared by immersion of silicate glass samples in a molten salt bath of molar concentration 10% AgNO₃ in NaNO₃ at T = 320 °C. Scanning electron microscopy measurement in electron diffraction scattering (EDS) configuration confirms the silver presence in the various glasses, and the UV/visible absorption gives the evolution of the spectra after ionic exchange and plasmon resonance apparition after annealing. After annealing at 450 °C, both diagnostics inform us about the particles’ formation and the silver rediffusion. Silver nanoparticle growth after annealing prior leads to photoluminescence exaltation and quenching for the longest exchange samples. Subsequently, we propose potential mechanisms of the nanoparticle formation with an initial depolymerization of the silicate network during the ionic exchange and repolymerization during annealing.     

Alpha-interferon in Kikuchi’s disease

In Japan, histiocytic necrotizing lymphadenitis (Kikuchi’s disease) is a relatively common reactive lesion affecting lymph nodes, but the histogenesis and pathogenesis of the disease have not been clarified. Alpha-interferon has a role in the body’s defense against, viral infections. Using a polyclonal antibody to human alpha-interferon, we found numerous cells, mainly histiocytes, containing alpha-interferon in affected foci in the lymph nodes from 24 patients with Kikuchi’s disease. Tubuloreticular structures, thought by some authors to be associated with the production of interferon, were detected by electron microscopy in histiocytes, activated lymphocytes and vascular endothelial cells in the affected foci. These results suggested that the formation of tubuloreticular structures is a secondary phenomenon following stimulation by alpha-interferon. Further, the activity of 2′–5′ oligoadenylate synthetase, which is induced by alpha-interferon and enhanced during the early or active stage of viral infection, showed increased levels of activity in the active stage of Kikuchi’s disease and decreased to normal levels in the convalescent stage 2 weeks later. These results suggested the possibility of a viral etiology for Kikuchi’s disease.