Surface plasmon coupling with radiating dipole for enhancing the emission efficiency of a light-emitting diode

The experimental demonstrations of light-emitting diode (LED) fabrication with surface plasmon (SP) coupling with the radiating dipoles in its quantum wells are first reviewed. The SP coupling with a radiating dipole can create an alternative emission channel through SP radiation for enhancing the effective internal quantum efficiency when the intrinsic non-radiative recombination rate is high, reducing the external quantum efficiency droop effect at high current injection levels, and producing partially polarized LED output by inducing polarization-sensitive SP for coupling. Then, we report the theoretical and numerical study results of SP-dipole coupling based on a simple coupling model between a radiating dipole and the SP induced on a nearby Ag nanoparticle (NP). To include the dipole strength variation effect caused by the field distribution built in the coupling system (the feedback effect), the radiating dipole is represented by a saturable two-level system. The spectral and dipole-NP distance dependencies of dipole strength variation and total radiated power enhancement of the coupling system are demonstrated and interpreted. The results show that the dipole-SP coupling can enhance the total radiated power. The enhancement is particularly effective when the feedback effect is included and hence the dipole strength is increased.

Differential gene expression between the porcine morula and blastocyst

The survival and development of pre-implantation embryos are determinant factors affecting the outcome of animal reproduction. It is essential to transfer the expression of the genetic material from maternal sources, that is the ovum to the zygote before implantation to ensure successful development. Differentiation and transformation of blastomeres initiated during the morula and blastocyst stages is an important step of the embryonic development prior to implantation. We collected morula and early blastocyst samples from pure-bred Landrace pigs in vivo to study the differential gene expression patterns at these two stages. Total RNA was extracted from individual embryos and two rounds of amplification were employed. Two micrograms of antisense RNA, targets, were prepared and hybridized with each of four custom made oligo microarrays representing 24,000 porcine genes. The analyses of replicate hybridizations showed that among the 24,000 genes, 162 genes were expressed fivefold or greater in the morula compared to early blastocysts and 2126 genes were expressed fivefold or greater in early blastocysts compared to the morula. Of these differentially expressed genes, 1429 genes were functionally annotated with related human Gene Ontology terms. In addition to basic metabolic processes, genes related to signal transduction, transportation and cell differentiation were found in both stages and were up-regulated as embryo development proceeded. Real time polymerase chain reaction was utilized to quantify 12 genes differentially expressed in the 2 embryonic stages and validated the reliability of major evidences shown in microarrays. In conclusion, we have obtained a preliminary landscape of genes differentially expressed during the transition from morula to early blastocysts in pigs and showed a generally increased transcriptional activity, perhaps in preparation for implantation. Our results provide an opportunity to study the functions of these genes in relation to the development and survival of pre-implantation porcine embryos.

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM (M = Ti, Nb, Hf, and Ta) thin films

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM thin films (M = Ti, Nb, Hf, and Ta) have been studied. For (Fe0.55Co0.45)(100-x)B(x) (x = 5-15) thin films, with the increase of B content, the resistivity was increased because B could decrease the crystallinity of the films. The (Fe0.55Co0.45)90B10 thin film showed the optimum properties, where 4piM(s) = 16.1 kG, H(ce) = 64.2 Oe, H(ch) = 13.5 Oe, H(k) = 310 Oe and p = 338 microomega-cm. To reduce the coercivity of the film, the elements M, including Ti, Nb, Hf, and Ta, were selected to substitute for B in the FeCoB films. It was found that (Fe0.55Co0.45)90B6Ti2Nb2 thin film after annealing at a temperature of 200 degrees C for 30 min showed the optimal properties, where 4piM(s) = 15.8 kG, H(ce) = 4.8 Oe, H(ch) = 3.6 Oe, H(k) = 224 Oe and p = 290 microomega-cm. The theoretically calculated ferromagnetic resonance frequency of the developed films can be higher than 5 GHz.

Gene tree discordance of wild and cultivated Asian rice deciphered by genome-wide sequence comparison

Although a large number of genes are expected to correctly solve a phylogenetic relationship, inconsistent gene tree topologies have been observed. This conflicting evidence in gene tree topologies, known as gene tree discordance, becomes increasingly important as advanced sequencing technologies produce an enormous amount of sequence information for phylogenomic studies among closely related species. Here, we aim to characterize the gene tree discordance of the Asian cultivated rice Oryza sativa and its progenitor, O. rufipogon, which will be an ideal case study of gene tree discordance. Using genome and cDNA sequences of O. sativa and O. rufipogon, we have conducted the first in-depth analyses of gene tree discordance in Asian rice. Our comparison of full-length cDNA sequences of O. rufipogon with the genome sequences of the japonica and indica cultivars of O. sativa revealed that 60% of the gene trees showed a topology consistent with the expected one, whereas the remaining genes supported significantly different topologies. Moreover, the proportions of the topologies deviated significantly from expectation, suggesting at least one hybridization event between the two subgroups of O. sativa, japonica and indica. In fact, a genome-wide alignment between japonica and indica indicated that significant portions of the indica genome are derived from japonica. In addition, literature concerning the pedigree of the indica cultivar strongly supported the hybridization hypothesis. Our molecular evolutionary analyses deciphered complicated evolutionary processes in closely related species. They also demonstrated the importance of gene tree discordance in the era of high-speed DNA sequencing.

A GaN photonic crystal membrane laser

The implementation of a series of optically pumped GaN photonic crystal (PhC) membrane lasers is demonstrated at room temperature. The photonic crystal is composed of a scalene-triangular arrangement of circular holes in GaN. Three defect structures are fabricated for comparing their lasing characteristics with those of perfect PhC. It is observed that all the lasing defect modes have lasing wavelengths very close to the band-edge modes in the perfect PhC structure. Although those lasing modes, including band-edge and defect modes, have different optical pump thresholds, different lasing spectral widths, different quality factors (Q factors), and different polarization ratios, all their polarization distributions show maxima in the directions around one of the hole arrangement axes. The similar lasing characteristics between the band-edge and defect modes are attributed to the existence of extremely narrow partial band gaps for forming the defect modes. Also, the oriented polarization properties are due to the scalene-triangle PhC structure. In one of the defect lasing modes, the lasing threshold is as low as 0.82 mJ cm(-2), the cavity Q factor is as large as 1743, and the polarization ratio is as large as 25.4. Such output parameters represent generally superior lasing behaviors when compared with previously reported implementations of similar laser structures.

Au nanorings for enhancing absorption and backscattering monitored with optical coherence tomography

Preparation of a high-concentration Au nanoring (NR) water solution and its applications to the enhancement of image contrast in optical coherence tomography (OCT) and the generation of the photothermal effect in a bio-sample through localized surface plasmon (LSP) resonance are demonstrated. Au NRs are first fabricated on a sapphire substrate with colloidal lithography and secondary sputtering of Au, and then transferred into a water solution through a liftoff process. By controlling the NR geometry, the LSP dipole resonance wavelength in tissue can cover a spectral range of 1300 nm for OCT scanning of deep tissue penetration. The extinction cross sections of the fabricated Au NRs in water are estimated to give levels of 10(-10)-10(-9) cm(2) near their LSP resonance wavelengths. The fabricated Au NRs are then delivered into pig adipose samples for OCT scanning. It is observed that, when resonant Au NRs are delivered into such a sample, LSP resonance-induced Au NR absorption results in a photothermal effect, making the opaque pig adipose cells transparent. Also, the delivered Au NRs in the intercellular substance enhance the image contrast of OCT scanning through LSP resonance-enhanced scattering. By continuously OCT scanning a sample, both photothermal and image contrast enhancement effects are observed. However, by continually scanning a sample with a low scan frequency, only the image contrast enhancement effect is observed.

Absorption enhancement of an amorphous Si solar cell through surface plasmon-induced scattering with metal nanoparticles

The simulation results of absorption enhancement in an amorphous-Si (a-Si) solar cell by depositing metal nanoparticles (NPs) on the device top and embedding metal NPs in a layer above the Al back-reflector are demonstrated. The absorption increase results from the near-field constructive interference of electromagnetic waves in the forward direction such that an increased amount of sunlight energy is distributed in the a-Si absorption layer. Among the three used metals of Al, Ag, and Au, Al NPs show the most efficient absorption enhancement. Between the two used NP geometries, Al nanocylinder (NC) are more effective in absorption enhancement than Al nanosphere (NS). Also, a random distribution of isolated metal NCs can lead to higher absorption enhancement, when compared with the cases of periodical metal NC distributions. Meanwhile, the fabrication of both top and bottom Al NCs in a solar cell results in further absorption enhancement. Misalignments between the top and bottom Al NCs do not significantly reduce the enhancement percentage. With a structure of vertically aligned top and bottom Al NCs, solar cell absorption can be increased by 52%.

Visfatin regulates genes related to lipid metabolism in porcine adipocytes

Visfatin is a visceral adipose tissue-specific adipocytokine that plays a positive role in attenuating insulin resistance by binding to the insulin receptor. Visfatin has been suggested to play a role in the regulation of lipid metabolism and inflammation; however, the mechanism remains unclear. We investigated the effects of visfatin on the regulation of gene expression in cultured porcine preadipocytes and differentiated adipocytes. In preadipocytes, the mRNA abundance of lipoprotein lipase and PPARgamma were significantly increased by visfatin or insulin treatment after 8 d (all P < 0.05). In the presence of insulin, the mRNA abundance of adipocyte fatty acid-binding protein was 24.7-fold greater than in the untreated group (P < 0.05), whereas visfatin alone had no effect on adipocyte fatty acid-binding protein mRNA abundance. Adipocyte differentiation was induced by insulin treatment for 8 d. In differentiated porcine adipocytes, exposure to insulin or visfatin for 24 h increased (P < 0.05) fatty acid synthase mRNA abundance but had no effect on the expression of sterol regulatory element binding-protein 1c mRNA. We also found a 5.8-fold upregulation of IL-6 expression in porcine adipocytes after 24 h of treatment with visfatin (P < 0.05). These results demonstrated that visfatin upregulated lipoprotein lipase expression in preadipocytes, potentially facilitating lipid uptake, and increased the gene expression of fatty acid synthase in differentiated adipocytes to potentially enhance lipogenic activity. Furthermore, visfatin can upregulate IL-6 expression in differentiated porcine adipocytes. The information presented in this study provides insights into the roles of visfatin in lipid metabolism in pigs.

Enhancing InGaN-based solar cell efficiency through localized surface plasmon interaction by embedding Ag nanoparticles in the absorbing layer

The use of localized surface plasmon (LSP) interaction for significantly enhancing InGaN absorption near its band edge and the overall efficiency of an InGaN-based solar cell by embedding Ag nanoparticles (NPs) in the InGaN absorbing layer is numerically demonstrated. The generation of LSP resonance on the embedded Ag NPs and the NP scattering can produce a field distribution in the InGaN layer for enhancing absorption. It is shown that the embedded Ag NPs do not significantly affect the transport of the photo-generated carriers. The distortion of static electrical stream lines in the solar cell due to the embedded Ag NP leads to a decrease of photocurrent by only a few percents. Based on the material parameter values we use, unless the surface recombination velocity at the interface between the Ag NP and surrounding InGaN is extremely high, Ag NP embedment in the absorbing layer of an InGaN-based solar cell can enhance its efficiency by up to 27%. Such an increase is significantly larger than that achieved by depositing metal NP on the top surface of a solar cell.

Diagnosis of oral submucous fibrosis with optical coherence tomography

The epithelium (EP) thickness and the standard deviation (SD) of A-mode scan intensity in the laminar propria (LP) layer are used as effective indicators for the diagnosis of oral submucous fibrosis (OSF) based on the noninvasive clinical scanning of a swept-source optical coherence tomography (OCT) system of approximately 6 mum in axial resolution (in tissue) and 103 dB in sensitivity. Compared with the corresponding parameters in healthy oral mucosal mucosa, in OSF mucosa, the EP thickness becomes smaller and the SD of A-mode scan intensity in the LP layer (LP SD) also becomes smaller. The LP SD can also be used for effectively differentiating OSF (small LP SD) from lesion (large LP SD). This application is particularly useful in the case of a lesion without a clear surface feature. Meanwhile, the use of the SD of A-mode scan intensity in the EP layer (EP SD) can further help in differentiating OSF (medium EP SD) from healthy oral mucosal (small EP SD) and lesion (large EP SD) conditions. Compared with the conventional method of maximum mouth opening measurement, the use of the proposed OCT scanning results can be a more effective technique for OSF diagnosis.

Fabrication of sphere-like Au nanoparticles on substrate with laser irradiation and their polarized localized surface plasmon behaviors

The fabrications of sphere-like Au nanoparticles (NPs) on sapphire, GaN, and SiO(2) substrates through the irradiation of a few pulses of 266-nm laser onto Au thin films deposited on the substrates are demonstrated. The top-view diameter, contact angle on substrate, surface population density, and surface coverage percentage of the NPs can be controlled by the Au thin film thickness, laser energy density, substrate choice, and the gas or liquid, in which the Au thin film is immersed during laser irradiation. Optical transmission measurements show clear in-plane and out-of-plane localized surface plasmon resonance (LSPR) features, including the air resonance feature dictated by the gas or liquid immersing the NPs during transmission measurement, the in-plane substrate resonance feature controlled by the substrate material and the contact angle, and the out-of-plane resonance feature, which is strongly influenced also by the substrate material and the contact angle. Numerical simulations based on the finite-element method using the experimental parameters show highly consistent LSPR spectral positions and their variation trends. From the simulation results, one can also observe the relative importance between NP absorption and scattering in contributing to the extinction. This simple laser-irradiation method for fabricating sphere-like Au NPs of no aggregation and of strong adhesion to the substrate is useful for developing polarization-sensitive LSPR bio-sensing.

Secretion profiles of venom alkaloids in Solenopsis geminata (Hymenoptera: Formicidae) in Taiwan

Solenopsis geminata (F.) was introduced into southern Taiwan decades ago and has continued to threaten the residents. Although the venom compositions of various fire ant species have been studied, the effects of environmental cues on the secretion pattern have received relatively little attention in an area with subtropical climate and high humidity, such as Taiwan. This study characterizes the effects of temperature and season on the venom compositions of S. geminata in Taiwan. Pure venom was sampled by using a microcapillary pipette and immersing the whole ant in hexane and subjected to gas chromatography-mass spectrometry analysis. The results showed that the ratio of cis C(11) to trans C(11) alkaloids in major workers was significantly higher than that in minor workers. No significant differences could be found in either the relative alkaloids content or the ratio of cis C(11) to trans C(11) alkaloids in venom of minor workers while rearing at four temperature conditions. Nevertheless, the ratio of cis C(11) to trans C(11) alkaloids in the venom of minor workers was the highest in spring and the lowest in winter. The results also showed that the body length, abdomen length, head length, head width, and venom volume differed significantly between major workers and minor workers of S. geminata. The venom volumes of these two castes were positively correlated with their body sizes.

Effective energy coupling and preservation in a surface plasmon-light emitter coupling system on a metal nanostructure

The simulation results of the coupling of a radiation dipole with a surface plasmon (SP), which is induced on a metal/dielectric interface of a single groove (SG) plus a grating structure, are demonstrated. With the SG structure, the dipole can effectively couple energy into an SP feature, which has a mixed nature of localized surface plasmon (LSP) and surface plasmon polariton (SPP). The SPP energy is confined by a grating structure with a well designed grating period and position. With such a cavity configuration, the SPP energy can be well preserved. Both the dipole-SP coupling behaviors in the frequency and time domains are numerically illustrated. The results are useful for designing a metal/dielectric interface nanostructure for implementing a SPASER (surface plasmon amplification by stimulated emission of radiation) system.

Study on the decay mechanisms of surface plasmon coupling features with a light emitter through time-resolved simulations

The transient behaviors of the dipole coupling with surface plasmon (SP) features in an Ag/dielectric-interface grating structure in order to understand the characteristics of those dipole-coupling features are demonstrated. In particular, the major decay mechanisms of those coupling features can be identified. For comparison, the time-resolved behaviors of the resonant surface plasmon polariton (SPP) coupling feature on a flat interface are also illustrated. Among the three major grating-induced SP-dipole coupling features, two of them are identified to be localized surface plasmons (LSPs). The third one is a grating-assisted SPP, which shows two decay components, corresponding to the first stage of SPP in-plane propagation and the second stage of coupling system decay. In all the dipole coupling features, metal dissipation can dominate the energy relaxation process, depending on the assumption of damping factor. All the dissipation rates are proportional to the assumed damping factor in the Drude model of the metal. The dissipation rates of the LSP and resonant SPP features are about the same as the damping rate, implying their local electron oscillation natures. The dissipation rate of the grating-assisted SSP feature is consistent with theoretical calculation. In the LSP features under study, dielectric-side emission is prominent. The coupled energy in the grating-assisted SPP feature can be efficiently stored in the coupling system due to its low emission efficiency and effective energy confinement through grating diffraction.

Effective indicators for diagnosis of oral cancer using optical coherence tomography

A swept-source optical coherence tomography system is used to clinically scan oral precancer and cancer patients for statistically analyzing the effective indicators of diagnosis. Three indicators are considered, including the standard deviation (SD) of an A-mode scan signal profile, the exponential decay constant (alpha) of an A-mode-scan spatial-frequency spectrum, and the epithelium thickness (T) when the boundary between epithelium and lamina propria can still be identified. Generally, in abnormal mucosa, the standard deviation becomes larger, the decay constant of the spatial-frequency spectrum becomes smaller, and epithelium becomes thicker. The sensitivity and specificity of the three indicators are discussed based on universal and individual relative criteria. It is found that SD and alpha are good diagnosis indicators for moderate dysplasia and squamous cell carcinoma. On the other hand, T is a good diagnosis indicator for epithelia hyperplasia and moderate dysplasia.

Effective indicators for diagnosis of oral cancer using optical coherence tomography

A swept-source optical coherence tomography system is used to clinically scan oral precancer and cancer patients for statistically analyzing the effective indicators of diagnosis. Three indicators are considered, including the standard deviation (SD) of an A-mode scan signal profile, the exponential decay constant (alpha) of an A-mode-scan spatial-frequency spectrum, and the epithelium thickness (T) when the boundary between epithelium and lamina propria can still be identified. Generally, in abnormal mucosa, the standard deviation becomes larger, the decay constant of the spatial-frequency spectrum becomes smaller, and epithelium becomes thicker. The sensitivity and specificity of the three indicators are discussed based on universal and individual relative criteria. It is found that SD and alpha are good diagnosis indicators for moderate dysplasia and squamous cell carcinoma. On the other hand, T is a good diagnosis indicator for epithelia hyperplasia and moderate dysplasia.

Localized surface plasmon-induced emission enhancement of a green light-emitting diode

The output enhancement of a green InGaN/GaN quantum-well (QW) light-emitting diode (LED) through the coupling of a QW with localized surface plasmons (LSPs), which are generated on Ag nanostructures on the top of the device, is demonstrated. The suitable Ag nanostructures for generating LSPs of resonance energies around the LED wavelength are formed by controlling the Ag deposition thickness and the post-thermal-annealing condition. With a 20 mA current injected onto the LED, enhancements of up to 150% in electroluminescence peak intensity and of 120% in integrated intensity are observed. By comparing this with a similar result for a blue LED previously published, it is confirmed that surface plasmon coupling for emission enhancement can be more effective for an InGaN/GaN QW of lower crystal quality, which normally corresponds to the emission of a longer wavelength.

Delineation of an oral cancer lesion with swept-source optical coherence tomography

We demonstrate the ex vivo imaging of an oral cancerous sample with a swept-source optical coherence tomography (SS-OCT) system. With the axial resolution of 8 microm in free space and system sensitivity of 108 dB, we can well distinguish the normal and abnormal tissue portions in a sample. In particular, we analyze the lateral variation of A-scan profiles to show two parameters of SS-OCT signal for delineating an oral cancer lesion. One of the parameters is the decay constant in the exponential fitting of the SS-OCT signal intensity along depth. This decay constant decreases as the A-scan point moves laterally across the margin of a lesion. The other parameter is the standard deviation of the SS-OCT signal intensity fluctuation in an A-scan. This parameter increases significantly when the A-scan point is moved across the transition region between the normal and abnormal portions. Such parameters are useful for determining the margins of oral cancer.

Measurement of the hemoglobin oxygen saturation level with spectroscopic spectral-domain optical coherence tomography

We report the measurement of the hemoglobin (Hb) oxygen saturation level in human blood with a spectroscopic spectral-domain optical coherence tomography (SSD-OCT) system based on the crossover behavior of Hb and oxyhemoglobin (HbO(2)) absorption coefficients around 800 nm. By calculating the ratio of the exponential decay constant of A-mode scan signal in the long-wavelength range (>800 nm) over that in the short-wavelength range (<800 nm), the relative oxygen saturation level of Hb can be calibrated. Such a relative level can be used for practical diagnosis application after a golden standard is built by comparing the variation of the OCT result with that of a conventional method, such as the use of a blood gas analyzer. In our experiment, the variation curve based on the SSD-OCT measurement, which has the advantages of noninvasive, real-time, and high-resolution measurements, is coincident with that of using a commercial blood gas analyzer.

Fabrication of high-aspect-ratio Fresnel zone plates by e-beam lithography and electroplating

The fabrication of gold Fresnel zone plates, by a combination of e-beam lithography and electrodeposition, with a 30 nm outermost zone width and a 450 nm-thick structure is described. The e-beam lithography process was implemented with a careful evaluation of applied dosage, tests of different bake-out temperatures and durations for the photoresist, and the use of a developer without methylisobutylketone. Electrodeposition with a pulsed current mode and with a specially designed apparatus produced the desired high-aspect-ratio nanostructures. The fabricated zone plates were examined by electron microscopy and their performances were assessed using a transmission X-ray microscope. The results specifically demonstrated an image resolution of 40 nm.

Recent progress in the development of inhibitors of human immunodeficiency virus (HIV) integrase for the management of HIV infection

Current therapy of acquired immune deficiency syndrome (AIDS) involves the use of a combination of at least three antiviral drugs to inhibit Human immunodeficiency virus 1 and 2 (HIV-1 and 2, in short HIV) replication via targeting of viral reverse transcriptase and protease. However, all anti-HIV drugs give rise to the new retroviral resistant strains. Therefore, new therapeutic agents against the emerging resistant HIV strains without secondary effects are very much needed. In HIV infection, the integration of viral DNA obtained from RNA genome into the chromosome of the host cell by viral integrase (IN) is essential for an effective viral replication. Moreover, no cellular IN has been found in the cells suggesting that viral IN appears to be one of the best candidates for the development of an antiviral drug. In recent years, promising results have proved that IN inhibitors are useful for treatment of retroviral infections. In this review, we briefly introduce IN and summarize potential inhibitors of IN, which are classified into several groups according to their origin and chemical structure. The resistance to the IN inhibitors is also discussed. Currently, several IN inhibitors are either being used in the clinical treatment or tested in clinical trials. Nevertheless, a great effort must be made to elicit wide knowledge with respect to the design of better viral inhibitors and the synthesis of new chemical derivatives with an anti-HIV activity.

Tissue birefringence of hypercholesterolemic rat liver measured with polarization-sensitive optical coherence tomography

We measure in vitro tissue birefringence in the liver of hypercholesterolemic rats with polarization-sensitive optical coherence tomography. Tissue birefringence is determined by measuring the phase retardation as a function of tissue depth. The birefringence of such a sample is usually due to the narrow fibrous structures that cannot be resolved by a standard optical coherence tomography system. Anisotropic structures are formed in the hypercholesterolemic rat liver, which is quite different from the isotropic nature of healthy liver. Birefringence is evaluated to give an order of magnitude of 4.48x10(-4) at 790 nm in hypercholesterolemic rat liver. The infiltration of macrophages and increased collagen deposition should be major causes for tissue birefringence in hypercholesterolemic liver.

28-Day oral toxicity study of the aqueous extract from spider brake (Pteris multifida Poiret) in rats

Spider brake (Pteris multifida Poiret) is a very important folk herb and a constituent in most of the traditional herbal beverage formulas in Taiwan; however, little toxicological information is available regarding the safety following repeated exposure. The present study was conducted to evaluate the toxicity of aqueous extract from spider brake (SB) in Sprague-Dawley rats on dietary oral gavage at concentrations of 100, 500, and 1000 mg/kg b.w. day for 28 days. There were no adverse effects on general condition, growth, feed and water consumption, feed conversion efficiency, red blood cell and clotting potential parameters, clinical chemistry values, and organ weights except for neutrophils and lymphocytes being slightly diminished in male and female rats at the highest dose, respectively. Necropsy and histopathology findings revealed no treatment-related changes in any of the organs. The results obtained in this study allowed us to conclude that the SB properly utilized in the traditional oral administration could be devoid of any toxic risk.