Maximal Cr Research Articles

Quasi Yamabe Solitons on CR Submanifolds of Maximal CR Dimension in Kähler Manifolds

In this paper we give necessary and sufficient conditions for a CR submanifold of maximal CR dimension in arbitrary Kähler manifold to admit (quasi-)Yamabe structure, with naturally chosen soliton vector field. When the ambient manifold is a non-flat complex space form, we give a complete classification of such solitons, under certain conditions.

Recyclable adsorption removal and fluorescent monitoring of hexavalent chromium by electrospun nanofibers membrane derived from Tb3+ coordinating polyarylene ether amidoxime

Emerging technologies or advanced materials which can simultaneously adsorb and detect highly toxic Cr(VI) are urgently in demand for environmental remediation. Herein, we have designed and synthesized a functional polyarylene ether with aromatic main chain and pendent carboxyl groups along with amidoxime group that can be coordinated with different metal ions. Thanks to its versatile activation of the lanthanide ions' inherent fluorescence and good processability, the fluorescent nanofiber membranes with competitive Cr(VI) adsorption and detection performance have been fabricated via one-step electrospinning of mixed solution containing synthesized polymer and terbium salt. More specifically, the optimized nanofiber membrane exhibits a maximal Cr(VI) adsorption of 278.2 mg/g and specific detection for hexavalent chromium down to 11.76 nM. More importantly, the prepared fluorescent nanofiber membranes can be easily re-generated and re-used for both Cr(VI) adsorption and detection for five times. Given the unique advantages of easy fabrication, competitive dual functionalities as well as good reusability of electrospun fluorescent nanofiber membranes, the present work basically opens up new insight in the design of multifunctional recyclable material for the remediation of heavy metal pollution.

Potential for efficient microbial remediation of Cr (VI) in wastewater using Deinococcus wulumuqiensis R12.

This study aimed to investigate the potential of Deinococcus wulumuqiensis R12 (D. wulumuqiensis R12) as a bioadsorbent for Cr (VI) removal from aqueous solutions. Effects of various factors including initial concentration of Cr (Ⅵ), pH, adsorbent dosage and time were explored. The maximal Cr removal efficiency was achieved by adding D. wulumuqiensis R12 to the solution at pH 7.0 for 24h, with an initial Cr concentration of 7mg L-1. Characterization of bacterial cells showed that Cr was adsorbed to the surface of D. wulumuqiensis R12 by combining with functional groups, such as carboxyl and amino groups on the surface. Furthermore, D. wulumuqiensis R12 was able to keep its bioactivity in the presence of Cr and tolerate Cr concentrations as high as 60mg L-1. D. wulumuqiensis R12 demonstrates a comparatively high adsorption capacity for Cr (VI). Under the optimized conditions, the removal ratio reached 96.4% with 7mg L-1 Cr (VI), and the maximal biosorption capacity was 2.65mg g-1. More importantly, it was found that D. wulumuqiensis R12 still had strong metabolic activity and maintained its viability after adsorbing Cr (VI), which is beneficial for biosorbent stability and reuse.

The superior performance of silica gel supported nano zero-valent iron for simultaneous removal of Cr (VI)

Pure nano zero-valent iron (NZVI) was fabricated under optimum conditions based on material production yield and its efficiency toward acid blue dye-25 decolorization. The optimum prepared bare NZVI was immobilized with two different supports of silica and starch to fabricate their composites nanomaterials. The three different prepared zero-valent iron-based nanomaterials were evaluated for removal of hexavalent chromium (Cr(VI)). The silica-modified NZVI recorded the most outstanding removal efficiency for Cr(VI) compared to pristine NZVI and starch-modified NZVI. The removal efficiency of Cr(VI) was improved under acidic conditions and decreased with raising the initial concentration of Cr(VI). The co-existence of cations, anions, and humic acid reduced Cr(VI) removal efficiency. The removal efficiency was ameliorated from 96.8% to 100% after adding 0.75 mM of H2O2. The reusability of silica-modified NZVI for six cycles of Cr(VI) removal was investigated and the removal mechanism was suggested as the physicochemical process. Based on Langmuir isotherm, the maximal Cr(VI) removal capacity attained 149.25 mg/g. Kinetic and equilibrium data were efficiently fitted using the pseudo-second-order and Langmuir models, respectively confirming the proposed mechanism. Diffusion models affirmed that the adsorption rate was governed by intraparticle diffusion. Adsorption thermodynamic study suggested the spontaneity and exothermic nature of the adsorption process. This study sheds light on the technology that has potential for magnetic separation and long-term use for effective removal of emerging water pollutants.

Efficacy of Transarterial Chemoembolization Combined with Molecular Targeted Agents for Unresectable Hepatocellular Carcinoma: A Network Meta-Analysis.

Simple SummaryLiver cancer is the second most common cause of cancer-related death, with hepatocellular carcinoma (HCC) being the most prevalent subtype. Transarterial chemoembolization (TACE) in combination with different tyrosine kinase inhibitors (TKIs) has recently been widely used for unresectable HCC (uHCC). However, studies investigating different combinations of agents have shown inconsistent results. Thus, we conducted a network meta-analysis to assess and compare the response of different agents in an uHCC setting. According to our results, TACE plus lenvatinib provides optimal treatment for uHCC, with the highest ranking based on OS, PFS, and DCR rates and the second-best ranking based on ORR rates.Transarterial chemoembolization (TACE) combined with tyrosine kinase inhibitors (TKIs) is the mainstay treatment for unresectable hepatocellular carcinoma (uHCC). However, studies investigating different combinations of agents have shown inconsistent results. Here, we used network meta-analysis (NMA) to compare different agents across 41 studies (36 cohort studies and five RCTs) in 11,540 patients. Multiple RCTs and cohort studies were searched to evaluate TACE combined with different TKIs. Outcomes of interest included overall survival (OS), progression-free survival (PFS), and tumor response. NMA used a random-effects consistency model to pool evidence from direct and indirect comparisons. Hazard ratio (HR) and relative risks (RR) with 95% confidence intervals (CI) were analyzed. Further, heterogeneity and publication bias analyses were performed and agents were ranked. TACE plus lenvatinib provided the maximal OS (Rank probability: 0.7559), PFS (Rank probability: 0.8595), CR (Rank probability: 0.4179), and DCR (Rank probability: 0.3857). TACE plus anlotinib demonstrated the highest PR (p = 0.62649) and ORR (p = 0.51158). SD was more often associated with TACE plus sorafenib (Rank probability: 0.601685). TACE plus lenvatinib provides optimal treatment for uHCC based on the highest ranking of OS, PFS, and DCR rates. However, given the lack of statistically significant OS benefit, shared decision making should include other TKIs as acceptable alternatives.

ZVI impregnation altered arsenic sorption by ordered mesoporous carbon in presence of Cr(Ⅵ): A mechanistic investigation

It is challenging to efficiently remove arsenate (As(Ⅴ)) and chromate (Cr(Ⅵ)) simultaneously. Herein, ordered mesoporous carbon (OMC) was fabricated with averaged pore diameter of 6.5 nm and surface area of 997 m2 g−1. Zerovalent iron (ZVI) impregnation reduced surface area of ZVI/OMC (432 m2 g−1) and increased ID/IG ratio by 13%. Maximal Cr(Ⅵ) and As(Ⅴ) sorption capacities at pH 3 were 0.66 and 0.019 mmol g−1 by OMC, and 0.71 and 0.39 mmol g−1 by ZVI/OMC, respectively. Reduction accounted for over 55% for Cr(Ⅵ) and As(Ⅴ) removal followed by complexation and precipitation. Better ZVI/OMC performance was ascribed to higher electron transfer rate and lower electrical resistance than OMC as per electrochemical analysis. Upon Cr(Ⅵ) introduction, As(Ⅴ) removal increased to 0.28 mmol g−1 by OMC, but decreased to 0.16 mmol g−1 by ZVI/OMC. OMC could preferably reduce CrO42− to Cr3+ by hydroxyl group, which enhanced its zeta potential facilitating As(Ⅴ) sorption. Regarding ZVI/OMC, Fe0 and Fe oxide in ZVI/OMC exhibited better affinity to As(Ⅴ), but the competition for the similar active sites resulted in compromised As(Ⅴ) and Cr(Ⅵ) removal. Thus, the novel OMC is advantageous for removal of binary As(Ⅴ) and Cr(Ⅵ), but ZVI/OMC is robust to detoxify single heavy metal.

Development of a cost-effective, recyclable and viable metal ion doped adsorbent for simultaneous adsorption and reduction of toxic Cr (VI) ions

Iron ions were doped on the rice husk for adsorption-cum-reduction of lethal Cr (VI) to less toxic and partially soluble Cr (III). Energy dispersive X-ray analysis and X-ray photoelectric spectroscopy disclosed the effective doping of iron on rice husk and significant reduction of Cr (VI) into Cr (III). Physico-chemical analysis exhibited that the surface of an iron doped rice husk was rough and in houses amino and hydroxyl moieties in majority together with high organic content. The maximum removal of Cr (VI) ions was observed in acidic range as the value of point zero charge was 3.32. The study of dimensionless numbers (φ, Nk and λ) disclosed that the Cr (VI) adsorption on iron coated rice husk was principally controlled by diffusion. The suitability of acidic pH indicated that heavy protonation at FeRH surface generated the electrostatic pull of negatively charged Cr (VI) species, which led to a favorable biosorption. Only 1.32% and 0.18% deviation in experimental results was observed for undoped and iron doped rice husk, respectively in artificial neural network’s correlation plot. The film and pore diffusivity coefficients along with Bangham’s model study revealed that the adsorption was film diffusion limited for both types of rice husks. The maximal Cr (VI) removal was found to be 81.56% for iron doped and 43.28% for undoped rice husk. The iron doped rice husk had high regeneration capacity up to three cycles of adsorption and desorption. Cr (VI) adsorption was chemisorptive, spontaneous, endothermic, favorable and multilayer in nature.

Modified Spruce Sawdust for Sorption of Hexavalent Chromium in Batch Systems and Fixed-Bed Columns.

This study investigated the potential use of spruce sawdust that was pretreated with diethylene glycol and sulfuric acid for the removal of hexavalent chromium from wastewater. The sawdust pretreatment process was conducted at different temperatures and times. The adsorbent was characterized by quantitative saccharification, scanning electron microscopy, and Brunauer–Emmet–Teller surface area analysis. Adsorption capacity was studied for both batch and column processes. The experimental adsorption isotherms were simulated using seven isotherm models, including Freundlich and Langmuir models. By using the Langmuir isotherm model, the maximal Cr(VI) adsorption capacity of organosolv-pretreated spruce sawdust (qm) was 318.3 mg g−1. Furthermore, the kinetic data were fitted to Lagergren, pseudo-second-order, and intraparticle diffusion models, revealing that the adsorption of Cr(VI) onto spruce sawdust pretreated with diethylene glycol and sulfuric acid is best represented by the pseudo-second-order kinetic model. Three kinetic models, namely, the Bohart–Adams model, Thomas model, and modified dose–response (MDR) model, were used to fit the experimental data obtained from the column experiments and to resolve the characteristic parameters. The Thomas adsorption column capacity of the sawdust was increased from 2.44 to 31.1 mg g−1 upon pretreatment, thus, demonstrating that organosolv treatment enhances the adsorption capability of the material.

Synthesis of gallic acid functionalized magnetic hydrogel beads for enhanced synergistic reduction and adsorption of aqueous chromium

Hexavalent chromium (Cr(VI)) is one class of highly toxicant heavy metal ion that severely threatens the environmental quality and human health. Herein, a class of magnetic hydrogel beads (MHB) has been facilely developed with poly(ethylenimine)/chitosan (PEI/CS) hydrogel as the substrate material and Fe3O4 as the incorporated magnetic nanoparticles, followed by covalently chemical modification with gallic acid (GA). The well-designed MHB was then evaluated for their performance for synergistic reduction and adsorptive removal of Cr(VI) from aqueous environment. Results showed that electrostatic attraction played a crucial role in adsorption of Cr(VI) onto MHB; meanwhile, the GA grafting could not only significantly accelerate the Cr(VI) reduction, but also facilitate the chelating adsorption of resultant trivalent chromium (Cr(III)) onto PEI/CS substrate due to the proton consumption accompanied by Cr(VI) reduction, resulting in the synergistic enhancement of total chromium (Cr(T)) sorption and Cr(VI) detoxification. The batch adsorption experiments revealed that the Cr(T) adsorption capacity increased with temperature rising and the pseudo-second-order kinetic and Langmuir models could well describe the Cr(T) sorption behaviors, suggesting a single-layer, exothermal, and chemical sorption process. Maximal Cr(VI) removal capacity of GA-functionalized MHB was estimated to be 476.2 mg∙g−1, exceeding most of other related adsorbents. Moreover, the GA-functionalized MHB exhibited satisfactory reusability with no remarkable loss in Cr(VI) removal efficiency after five cycles. As compared with other reported adsorbents, the newly synthesized GA-functionalized MHB was promising for chromium wastewater treatment due to its synergistic reduction and adsorption process, ultra-high Cr(VI) removal capacity, facile magnetic separation and superior recycling performance.

Preparation of highly-conductive pyrogenic carbon-supported zero-valent iron for enhanced Cr(Ⅵ) reduction

In this work, electron transfer (ET) moiety of PC was ascertained in chromate (Cr(Ⅵ)) reduction by zero-valent iron supported by pyrogenic carbon (PC) (ZVI/PC) prepared by pyrolysis of hematite (α-Fe2O3)-treated pinewood. X-ray diffraction analysis suggested successive phase transformation of α-Fe2O3→magnetite (Fe3O4)→wustite (FeO)→ZVI (Feo). Raman spectra and Brunauer–Emmett–Teller analysis revealed that ZVI/PC is characterized with more ordered graphitic carbon and greater surface area than pristine PC. Maximal Cr(Ⅵ) removal capacity (pH = 3) as predicted by Langmuir isotherm model were 5.78, 36.12 and 8.39 g kg−1 for PC, ZVI/PC and ZVI, respectively. ZVI/PC maintained significantly greater Cr(Ⅵ) removal capacity than ZVI and PC at pH 3–9, but Cr(Ⅵ) removal dropped rapidly to 6.78 g kg−1 at pH 4 and above. X-ray photoelectron spectroscopy and successive desorption of Cr-laden ZVI/PC and ZVI showed trivalent Cr was the dominant species, suggesting reduction was an important mechanism for Cr(Ⅵ) detoxification. Electrochemical analysis demonstrated that ZVI/PC exhibited greater Tafel corrosion rate and ET quantity, with lower electrical resistance. Besides, Cr(Ⅵ) reduction showed reversal trend with electrical resistance of ZVI/PC. To conclude, ET capacity was closely associated with electrical conductivity of ZVI/PC due to intensified conductive graphitic carbon structure of PC at higher pyrogenic temperatures.

Concurrent reduction-adsorption of chromium using m-phenylenediamine-modified magnetic chitosan: kinetics, isotherm, and mechanism.

Magnetic chitosan particles (MCS) were chemically grafted by m-phenylenediamine (mPD) forming a distinctive shell layer with abundant nitrogenous functional groups and used as an adsorbent for the effective removal of Cr(VI) from aqueous solution. By interaction among functional groups in the facile oxidative polymerization process, the grafting of mPD and its polymers on MCS surface was innovatively realized. Through Fourier-transformed infrared spectroscopy, energy dispersive spectrometer, X-ray photoelectron spectroscopy, etc., the chemical properties of MCS before and after modification were characterized and the concurrent reduction-adsorption mechanism in Cr(VI) adsorption by mPD-MCS was carefully analyzed. The maximal Cr(VI) removal performance of mPD-MCS reached 227.27mg/g, which was significantly better than that of the original MCS. The analysis indicated that Cr(VI) could be efficiently reduced to Cr(III) and the removal of Cr(VI) and Cr(III) was through adsorption and chelation simultaneously by mPD-MCS. Results also indicated that the concurrent reduction-adsorption was enhanced by protonation of nitrogenous functional groups under low pH. The obtained results suggest that mPD-MCS has a good potential in removal and detoxication of Cr(VI) from aqueous solutions.

Nb2O5 nanowires in-situ grown on carbon fiber: A high-efficiency material for the photocatalytic reduction of Cr(VI)

Niobium oxide nanowire-deposited carbon fiber (CF) samples were prepared using a hydrothermal method with amorphous Nb2O5·nH2O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), UV–visible spectroscopy (UV–vis), N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr(VI) was determined. Parameters such as pH value and initial Cr(VI) concentration could influence the Cr(VI) removal efficiency or adsorption capacity of the Nb2O5/carbon fiber sample obtained after hydrothermal treatment at 160°C for 14hr. The maximal Cr(VI) adsorption capacity of the Nb2O5 nanowire/CF sample was 115mg/g. This Nb2O5/CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr(VI) under UV-light irradiation: the Cr(VI) removal efficiency reached 99.9% after UV-light irradiation for 1hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr(VI) adsorption capacity and photocatalytic performance was related to its high surface area, abundant surface hydroxyl groups, and good UV-light absorption ability.

Totally geodesic submanifolds of regular Sasakian manifolds

Let Q m 1 denote the family of regular Sasakian manifolds whose base manifold M 2m is a compact symmetric space. We provide a classification of t he totally geodesic submanifolds of Q m 1 which are invariant, anti-invariant of maximal dimension or contact CR with respect to the Sasakian structure. Such submanifolds are closely related to complex and totally real totally geodesic submanifolds of the Hermitian symmetric space M 2m .

In vitrophysical, chemical, and biological evaluation of commercially available metal orthodontic brackets

ObjectiveThis in vitro study was undertaken to evaluate the physical, chemical, and biological properties of commercially available metal orthodontic brackets in South Korea, because national standards for these products are lacking.MethodsFour bracket brands were tested for dimensional accuracy, (manufacturing errors in angulation and torque), cytotoxicity, composition, elution, and corrosion: Archist (Daeseung Medical), Victory (3M Unitek), Kosaka (Tomy), and Confidence (Shinye Odontology Materials).ResultsThe tested rackets showed no significant differences in manufacturing errors in angulation, but Confidence brackets showed a significant difference in manufacturing errors in torque. None of the brackets were cytotoxic to mouse fibroblasts. The metal ion components did not show a regular increasing or decreasing trend of elution over time, but the volume of the total eluted metal ions increased: Archist brackets had the maximal Cr elution and Confidence brackets appeared to have the largest volume of total eluted metal ions because of excessive Ni elution. Confidence brackets showed the lowest corrosion resistance during potentiodynamic polarization.ConclusionsThe results of this study could potentially be applied in establishing national standards for metal orthodontic brackets and in evaluating commercially available products.

Environmental and Kinetic Parameters for Cr(VI) Bioreduction by a Bacterial Monoculture Purified from Cr(VI)-Resistant Consortium

Hexavalent chromium, Cr(VI), is toxic to living systems. Widespread contamination of water and soil by Cr(VI) present a serious public health problem. Chromium-resistant bacteria can reduce and detoxify Cr(VI). Twelve bacteria resistant to high concentrations of Cr(VI) were isolated from soil enrichment cultures. Environmental parameters and kinetic parameters of Cr(VI) bioreduction by one monoculture isolate, identified by 16S rRNA gene sequence as Bacillus sp. PB2, were studied. The optimal temperature for growth and Cr(VI) reduction was 35 degrees C. The isolate grew luxuriantly and substantially reduced Cr(VI) at initial pH 7.5 to 9. Maximal Cr(VI) bioreduction occurred at initial pH 8.0. Substantial Cr(VI) bioreduction was observed in salt media, but removal efficiency was inversely related to salt concentration (1-9%). Michaelis-Menten hyperbolic equation and the Lineweaver-Burk double reciprocal plot were comparatively employed to determine the k (m) and V (max) of Cr(VI) bioreduction. A k (m) of 82.5 microg mL(-1) and V (max) of 7.78 microg mL(-1) h(-1) were calculated by nonlinear regression analysis of the hyperbola curve. Linear regression analysis of the double reciprocal plot revealed k (m) and V (max) of 80.9 microg mL(-1) and 10.6 microg mL(-1) h(-1), respectively. Time course studies displayed about 90% reduction of Cr(VI) at an initial concentration of 8,000 microg L(-1) in 8 h, with an estimated t (1/2) of 4 h. Data from time course analysis of the rate of Cr(VI) bioreduction fitted zero-order model, and the kinetic constant k was calculated to be 840 microg L(-1) h(-1). The monoculture isolate, Bacillus sp. PB2, strongly reduces Cr(VI) and could be used for bioremediation of Cr(VI)-contaminated aquatic and terrestrial environments.

A comparative investigation on the properties of Cr-SBA-15 and CrO x/SBA-15

High-surface area and well-ordered mesoporous Cr-incorporated SBA-15 (Cr-SBA-15) and SBA-15-supported chromia (CrO x /SBA-15) with Cr surface density = 0.05–1.11 Cr-atom/nm 2 have been prepared, respectively, using the one-step synthesis and incipient wetness impregnation method, and characterized by AAS, XRD, BET, ESEM, TEM, XPS, laser Raman, UV-Vis, FT-IR, and H 2-TPR. It is observed that the Cr-SBA-15 and CrO x /SBA-15 samples showed an evolution of surface morphology from long chain-shaped to short rod-like and further to an irregularly spherical architecture at elevated Cr content, which might arise from the interaction of Cr ions or CrO x domains with SBA-15. There were co-presence of tetrahedrally coordinated mono- and poly-chromate (Cr 6+) as well as octahedrally coordinated Cr 3+ species in Cr-SBA-15 and CrO x /SBA-15, with the Cr 6+ species being dominant at Cr surface density ≤0.22 Cr-atom/nm 2 in Cr-SBA-15 and Cr ≤0.54 Cr-atom/nm 2 in CrO x /SBA-15, whereas the amount of the Cr 3+ species increased markedly at Cr surface density ≥0.53 Cr-atom/nm 2 due to the formation of crystal Cr 2O 3 phase. Maximal Cr incorporation into Cr-SBA-15 and one monolayer surface CrO x coverage on CrO x /SBA-15 occurred at Cr surface density ≤0.53 Cr-atom/nm 2 and <1.11 Cr-atom/nm 2, respectively. The CrO x /SBA-15 samples exhibited better reducibility than the Cr-SBA-15 samples, with the best reducibility exhibited at Cr surface densities of 0.54 and 0.12 Cr-atom/nm 2, respectively.

Thermal fatigue characteristics of gray cast iron with non-smooth surface treated by laser alloying of Cr powder

In order to enhance thermal fatigue resistance of gray cast iron with non-smooth surface further, researches on laser alloying of Cr powder with different scanning speed were performed to change both the composition and microstructure of non-smooth unit. The results indicated that there was an optimal scanning speed (2 mm/s) which can contribute maximal Cr element in alloyed zone, and increasing laser scanning speed resulted in smaller non-smooth unit and more pores in it. The microstructure in alloyed layer was composed of pre-eutectic phases, ledeburite eutectic and chromium carbides of Cr 23C 6. Thermal fatigue resistance of non-smooth sample is better than that of smooth sample, and among non-smooth samples, sample treated by laser Cr alloying has superior resistance to thermal fatigue compared with laser melting treated sample, in addition, the resistance of laser alloying non-smooth samples increases with scanning speed slowing.

Observation of Superconductivity in Highly Cr-Doped GaP Single Crystals

Studying bulk GaP, highly doped with Cr, and searching for possible ferromagnetic semiconductor in aim of spintronic applications, we found superconducting behavior of this material unexpectedly. GaP bulk crystals intentionally doped with Cr were grown by Liquid Encapsulated Czochralski (LEC) method. Metallic chromium was added to the melt with concentration in the range of 1 to 6x10 20 cm -3 . The resulting crystals were highly resistive at room temperature. X-ray diffraction (XRD) and magnetization techniques were applied to study these crystals. XRD measurements on (111) oriented samples employed high resolution multicrystal diffractometer and X-ray topography in classical transmission mode. Diffractometric results indicated good overall crystalline quality of the samples with some possible lattice parameter gradient. Transmission topography revealed network of cellular structure, usually observed in LEC grown GaAs crystals. This type of structure is well known to contain intentional or nonintentional dopants and other defects, segregated within the cell walls. It is highly possible that excess Cr was grouped in these regions. Magnetization studies were performed as a function of magnetic field, up to 6 T, and in the temperature range of 2-100 K, using SQUID magnetometer. All samples showed paramagnetic behaviour described well by the Brillouin function and ascribed to Cr impurity in GaP. Maximal Cr concentration calculated from saturation of magnetization curve was about 0.01%. Small antiferromagnetic (AFM) contribution to the total observed magnetization signal were found for samples with high initial Cr contents. It resulted most probably from metallic Cr precipitates. Chromium is known to be AFM element with Neel temperature TN=312K. However, unexpectedly, the total magnetization signal measured at T=2K was dominated by a quite strong diamagnetic response at low magnetic field. Moreover, typical behavior of superconductive system, i.e., diminishing of diamagnetic response at some critical magnetic field Bc, as well as characteristic Bc dependence on temperature was observed. We relate the observed superconductivity features to Cr precipitates, of peculiar shape and size, embedded in GaP lattice. Up to now there have been only reports about chromium superconductors with transition temperatures up to 10K in metastable fcc phase, fabricated by epitaxially sandwiching Cr between gold layers or in ion beam deposited Cr thin films on soft glass. Bulk Cr metal is not a superconductor. In recent years several ways to cause non superconducting elements to superconducting state have been found, including application of pressure, irradiation, quenched growth on a cold substrate, epitaxial templating in the form of thin film or chemical doping. This is the first report of Cr superconductivity in semiconductor host. It seems worth further studies because of interesting physics as well as possible applications including superconducting interconnections, junctions, and switches in integrated semiconductor-based devices.

Levi Form of CR Submanifolds of Maximal CR Dimension of Complex Space forms

Considering the Levi form on CR submanifolds of maximal CR dimension of complex space forms, we prove that on some remarkable real submanifolds of complex projective space the Levi form can never vanish and we determine all such submanifolds in the case when the ambient manifold is a complex Euclidean space.

Chromate reduction by chromium-resistant bacteria isolated from soils contaminated with dichromate.

Extensive use of hexavalent chromium [Cr(VI)] in various industrial applications has caused substantial environmental contamination. Chromium-resistant bacteria isolated from soils can be used to remove toxic Cr(VI) from contaminated environments. This study was conducted to isolate chromium-resistant bacteria from soils contaminated with dichromate and describes the effects of some environmental factors such as pH, temperature, and time on Cr(VI) reduction and resistance. We found that chromium-resistant bacteria can tolerate 2500 mg L(-1) Cr(VI), but most of the isolates tolerated and reduced Cr(VI) at concentrations lower than 1500 mg L(-1). Chromate reduction activity of whole cells was detected in five isolates. Most of these isolates belong to the genus Bacillus as identified by the 16S rRNA gene sequencing. Maximal Cr(VI) reduction was observed at the optimum pH (7.0-9.0) and temperature (30 degrees C) of growth. One bacterial isolate (Bacillus sp. ES 29) was able to aerobically reduce 90% of Cr(VI) in six hours. The Cr(VI) reduction activity of the whole cells of five isolates had a K(M) of 0.271 (2.61 mM) to 1.51 mg L(-1) (14.50 mM) and a V(max) of 88.4 (14.17 nmol min(-1)) to 489 mg L9-1) h(-1) (78.36 nmol min(-1)). Our consortia and monocultures of these isolates can be useful for Cr(VI) detoxification at low and high concentrations in Cr(VI)-contaminated environments and under a wide range of environmental conditions.