Second sound and the superfluid fraction in a Fermi gas with resonant interactions.

Superfluidity is a macroscopic quantum phenomenon occurring in systems as diverse as liquid helium and neutron stars. It occurs below a critical temperature and leads to peculiar behaviour such as frictionless flow, the formation of quantized vortices and quenching of the moment of inertia. Ultracold atomic gases offer control of interactions and external confinement, providing unique opportunities to explore superfluid phenomena. Many such (finite-temperature) phenomena can be explained in terms of a two-fluid mixture comprising a normal component, which behaves like an ordinary fluid, and a superfluid component with zero viscosity and zero entropy. The two-component nature of a superfluid is manifest in 'second sound', an entropy wave in which the superfluid and the non-superfluid components oscillate with opposite phases (as opposed to ordinary 'first sound', where they oscillate in phase). Here we report the observation of second sound in an ultracold Fermi gas with resonant interactions. The speed of second sound depends explicitly on the value of the superfluid fraction, a quantity that is sensitive to the spectrum of elementary excitations. Our measurements allow us to extract the temperature dependence of the superfluid fraction, a previously inaccessible quantity that will provide a benchmark for theories of strongly interacting quantum gases.

Cloning, expression and biochemical characterization of recombinant superoxide dismutase from Antarctic psychrophilic bacterium Pseudoalteromonas sp. ANT506.

In this study, a superoxide dismutase gene (PsSOD) from Pseudoalteromonas sp. ANT506 was cloned and over expressed in Escherichia coli. The PsSOD has an open reading frame of 582 bp with a putative product of 193 amino acid residue and an estimated molecular size of 21.4 kDa. His-tagged PsSOD was subsequently purified 12.6-fold by Ni-affinity chromatography and the yield of 22.9%. The characterization of the purified rPsSOD exhibited maximum activity at 30 °C and pH 8.0. The enzyme exhibited 13.9% activity at 0 °C and had high-thermo lability at higher than 50 °C. rPsSOD exhibited well capability to 2.5 M NaCl (62.4%). These results indicated that rPsSOD exhibited special catalytic properties.

Collective modes in a unitary Fermi gas across the superfluid phase transition.

We provide a joint theoretical and experimental investigation of the temperature dependence of the collective oscillations of first sound nature exhibited by a highly elongated harmonically trapped Fermi gas at unitarity, including the region below the critical temperature for superfluidity. Differently from the lowest axial breathing mode, the hydrodynamic frequencies of the higher-nodal excitations show a temperature dependence, which is calculated starting from Landau two-fluid theory and using the available experimental knowledge of the equation of state. The experimental results agree with high accuracy with the predictions of theory and provide the first evidence for the temperature dependence of the collective frequencies near the superfluid phase transition.

[Down-regulation of HDAC6 Expression Can Influence KG1α Cell Proliferation by Inhibiting ERK Pathway].

OBJECTIVE: To study the inhibitory effect of HDAC6 on proliferation of human leukemia KG1α and to explore its mechanism by ERK signaling pathways. METHODS: .The siRNA interference technology was used to inhibit the HDAC6 gene expression; the expression of HDAC6 and prateins of ERK signal pathway was detected by Western blot; the cell proliferation ability was detected by colony forming experiment and trypan blue staining; cell cycle was detected by FCM; and the expression of Ki67 was detected by immunofluorescence. RESULTS: Western blot showed that HDAC6 expression was up-regulated in leukemia cell lines in comparison with the healthy volunteers and bone marrow stromal cells (P＜0.05). Knockdown of HDAC6 significantly inhibited the proliferation and colony formation ability of leukemia cells, promoted cell arrest at G0/G1 phase. The Western blot and immunefluorescence showed that knockdown of HDAC6 suppressed the expression level of Ki67, CDK4, Cyclin D1 and enhanced the expression level of p16, p21, p-ERK (P＜0.05). CONCLUSION: Knockdown of HDAC6 significantly inhibits the proliferation, arrest the cell cycle at G0/G1 phase, and its mechanism probably relates with the activation of ERK signaling pathway.

attB site disruption in marine Actinomyces sp. M048 via DNA transformation of a site-specific integration vector.

An efficient conjugation method has been developed for the marine Actinomyces sp. isolate M048 to facilitate the genetic manipulation of the chandrananimycin biosynthesis gene cluster. A phiC31-derived integration vector pIJ8600 containing oriT and attP fragments was introduced into strain M048 by bi-parental conjugation from Escherichia coli ET12567 to strain M048. Transformation efficiency was (6.38+/-0.41)x10(-5) exconjugants per recipient spore. Analysis of eight exconjugants showed that the plasmid pIJ8600 was stably integrated at a single chromosomal site (attB) of the Actinomyces genome. The DNA sequence of the attB was cloned and shown to be conserved. The results of antimicrobial activity analysis indicated that the insertion of plasmid pIJ8600 seemed to affect the biosynthesis of antibiotics that could strongly inhibit the growth of E. coli and Mucor miehei (Tü284). HPLC-MS analysis of the extracts indicated that disruption of the attB site resulted in the complete abolition of chandrananimycin A-C production, proving the identity of the gene cluster. Instead of chandrananimycins, two bafilomycins were produced through disruption of the attB site from the chromosomal DNA of marine Actinomyces sp. M048.

Intergeneric conjugation in holomycin-producing marine Streptomyces sp. strain M095.

Marine Streptomyces are potential candidates for novel natural products and industrial catalysts. In order to set up biosynthesis approach for a holomycin-producing strain M095 isolated from Jiaozhou Bay, China, a genetic transformation system was established using intergeneric conjugation. The plasmid pIJ8600 consists of an origin of replication for Escherichia coli, a phage integrase directing efficient site-specific integration in bacterial chromosome, thiostrepton-induced promoter and an attP sequence. Using E. coli ET12567 (pUZ8002) carrying pIJ8600 as a conjugal donor, while it was mated with strain M095, pIJ8600 was mobilized to the recipient and the transferred DNA was also integrated into the recipient chromosome. The frequency of exconjugants was 1.9+/-0.13x10(-4) per recipient cell. Analysis of eight exconjugants showed pIJ8600 was stable integrated at a single chromosomal site (attB) of the Streptomyces genome. The DNA sequence of the attB was cloned and shown to be conserved. The results of growth and antimicrobial activity analysis indicated that the integration of pIJ8600 did not seem to affect the biosynthesis of antibiotics or other essential amino acids. To demonstrate the feasibility of above gene transfer system, the allophycocyanin gene (apc) from cyanobacterium Anacystis nidulans UTEX625 was expressed in strain M095, and the results indicated heterologous allophycocyanin could be expressed and folded effectively.

[Down-regulation of HDAC6 Expression Promotes Apoptosis of Human Leukemia K562 Cells].

OBJECTIVE: To study the promoting-apoptosis effect of HDAC6 on the human leukemia cells and its mechanism. METHODS: The siRNA interference technology was used to inhibit the expression of HDAC6 gene, the RT-PCR and Western blot were used to detect the expression of HDAC6 and related signal pathway proteins respectively, the flow cytometry and Hoechest staining were used to detect the apoptosis and morphology changes of K562 cells. RESULTS: Compared with the periphal blood monocyte and bone marrow stromal cells of healthy volunteers, the expression level of HDAC6 in leukemia cell lines was up-regulated significantly(P<0.05); the flow cytometry and Hoechest staining showed that after interference of HDAC6 gene, the apoptosis of K562 cells increased, moreover the cell morphology was changed; the Western blot detection showed that the interfering HDAC6 increased BAX/BCL-2 ratio and cleaved caspase 3 expression, and activated the MAPK, ATK, ERK signaling pathway. CONCLUSION: The interferance of HDAC6 can promote the K562 cell apoptosis, its mechanism may relate with activation of MAPK signaling pathway.

Anticoagulation and endothelial cell behaviors of heparin-loaded graphene oxide coating on titanium surface.

Owing to its unique physical and chemical properties, graphene oxide (GO) has attracted tremendous interest in many fields including biomaterials and biomedicine. The purpose of the present study is to investigate the endothelial cell behaviors and anticoagulation of heparin-loaded GO coating on the titanium surface. To this end, the titanium surface was firstly covered by the polydopamine coating followed by the deposition of the GO coating. Heparin was finally loaded on the GO coating to improve the blood compatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated that the heparin-loaded GO coating was successfully created on the titanium surface. The scanning electron microscopy (SEM) images indicated that a relative uniform GO coating consisting of multilayer GO sheets was formed on the substrate. The hydrophilicity of the titanium surface was enhanced after the deposition of GO and further improved significantly by the loading heparin. The GO coating can enhance the endothelial cell adhesion and proliferation as compared with polydopamine coating and the blank titanium. Loading heparin on the GO coating can significantly reduce the platelet adhesion and prolong the activated partial thromboplastin time (APTT) while not influence the endothelial cell adhesion and proliferation. Therefore, the heparin-loaded GO coating can simultaneously enhance the cytocompatibility to endothelial cells and blood compatibility of biomaterials. Because the polydopamine coating can be easily prepared on most of biomaterials including polymer, ceramics and metal, thus the approach of the present study may open up a new window of promising an effective and efficient way to promote endothelialization and improve the blood compatibility of blood-contact biomedical devices such as intravascular stents.

Effects of self-assembly of 3-phosphonopropionic acid, 3-aminopropyltrimethoxysilane and dopamine on the corrosion behaviors and biocompatibility of a magnesium alloy.

Magnesium based alloys are attracting tremendous interests as the novel biodegradable metallic biomaterials. However, the rapid in vivo degradation and the limited surface biocompatibility restrict their clinical applications. Surface modification represents one of the important approaches to control the corrosion rate of Mg based alloys and to enhance the biocompatibility. In the present study, in order to improve the corrosion resistance and surface biocompatibility, magnesium alloy (AZ31B) was modified by the alkali heating treatment followed by the self-assembly of 3-phosphonopropionic acid, 3-aminopropyltrimethoxysilane (APTMS) and dopamine, respectively. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectra (XPS) indicated that the molecules were successfully immobilized on the magnesium alloy surface by the self-assembly. An excellent hydrophilic surface was obtained after the alkali heating treatment and the water contact angle increased to some degree after the self-assembly of dopamine, APTMS and 3-phosphonopropionic acid, however, the hydrophilicity of the modified samples was better than that of the pristine magnesium substrate. Due to the formation of the passivation layer after the alkali heating treatment, the corrosion resistance of the magnesium alloy was obviously improved. The corrosion rate further decreased to varying degrees after the self-assembly surface modification. The blood compatibility of the pristine magnesium was significantly improved after the surface modification. The hemolysis rate was reduced from 56% of the blank magnesium alloy to 18% of the alkali heating treated sample and the values were further reduced to about 10% of dopamine-modified sample and 7% of APTMS-modified sample. The hemolysis rate was below 5% for the 3-phosphonopropionic acid modified sample. As compared to the pristine magnesium alloy, fewer platelets were attached and activated on the modified surfaces and the activated partial thromboplastin times (APTT) were prolonged to some degree. Furthermore, the modified samples showed good cytocompatibility. Endothelial cells exhibited the improved proliferative profiles in terms of CCK-8 assay as compared to those on the pristine magnesium alloy. The modified samples showed better endothelial cell adhesion and spreading than the pristine magnesium alloy. Taking all these results into consideration, the method of this study can be used to modify the magnesium alloy surface to improve the corrosion resistance and biocompatibility simultaneously.

Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling.

Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations.

Fabrication of anticoagulation layer on titanium surface by sequential immobilization of poly (ethylene glycol) and albumin.

This paper presents a simple method to sequentially immobilize poly (ethylene glycol) (PEG) and albumin on titanium surface to enhance the blood compatibility. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis indicated that PEG and albumin were successfully immobilized on the titanium surface. Water contact angle results showed a better hydrophilic surface after the immobilization. The immobilized PEG or albumin can not only obviously prevent platelet adhesion and activation but also prolong activated partial thromboplastin time (APTT), leading to the improved anticoagulation. Moreover, immobilization of albumin on PEG-modified surface can further improve the anticoagulation. The approach in the present study provides an effective and efficient method to improve the anticoagulation of blood-contact biomedical devices such as coronary stents.

Blood compatibility and interaction with endothelial cells of titanium modified by sequential immobilization of poly (ethylene glycol) and heparin.

In this study, poly(ethylene glycol) (PEG) and heparin were sequentially immobilized on a titanium surface by the carbodiimide covalent coupling method with the aim to improve the blood compatibility of titanium and enhance endothelial cell adhesion and proliferation. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed that PEG and heparin were successfully immobilized on the titanium surface. Compared to the pristine titanium, a highly hydrophilic layer was achieved after the immobilization, and the resulting heparin-PEG layer can significantly prevent human plasma fibrinogen adsorption. Analysis of platelet attachment to the modified surfaces, via scanning electron microscopy (SEM), showed strikingly fewer platelets attached to the PEG and heparin modified surfaces, compared to the control. The immobilized PEG and heparin effectively prolonged the activated partial thromboplastin time (APTT) and inhibit platelet activation significantly. Furthermore, the modified samples showed good cytocompatibility. Endothelial cells exhibited improved proliferative profiles in terms of a CCK-8 assay, as compared to those on the pristine titanium. The modified samples showed a better endothelial cell adhesion and spreading, than the pristine titanium. Therefore, the blood compatibility and cytocompatibility of the titanium surface can be enhanced by PEG immobilization and further, by subsequent heparin grafting. It could be concluded that the negatively charged heparin-PEG layer with excellent hydrophilicity could obviously improve the blood compatibility and enhance the endothelial cell adhesion and proliferation, and the approach of the present study is considered as an effective method to improve the hemocompatibility and cytocompatibility of biomaterials.

Improved anticoagulation of titanium by sequential immobilization of oligo(ethylene glycol) and 2-methacryloyloxyethyl phosphorylcholine.

Titanium and its alloys have been widely used for blood-contacting biomedical devices; however, their blood compatibility needs to be improved. In this study, titanium surface was modified by sequential immobilization of oligo(ethylene glycol) (OEG) and 2-methacryloyloxyethyl phosphorylcholine (MPC) to improve its anticoagulation. Water contact angle results showed an excellent hydrophilic surface after the immobilization. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) confirmed that OEG and MPC were successfully immobilized on titanium surface. Static platelet adhesion and APTT (activated partial thromboplastin time) experiments suggested that the anticoagulation of titanium was significantly enhanced by the immobilization of OEG and further by subsequent MPC grafting. The approach in the present study opens up a window of promising an effective and efficient method to improve the anticoagulation of blood-contact biomedical devices such as coronary stents.

Purification and characterization of an extracellular cold-active serine protease from the psychrophilic bacterium Colwellia sp. NJ341.

Colwellia sp. NJ341, isolated from Antarctic sea ice, secreted a cold-active serine protease. The purified protease had an apparent Mr of 60 kDa by SDS-PAGE and MALDI-TOF MS. It was active from pH 5-12 with maximum activity at 35 degrees C (assayed over 10 min). Activity at 0 degrees C was nearly 30% of the maximum activity. It was completely inhibited by phenylmethylsulfonyl fluoride.