Progressive failure analysis of perforated composite laminates considering nonlinear shear effect.

Composites are widely used in high performance structures such as aerospace structures due to their excellent properties. The analysis of failure evolution of composite perforated structures by finite element simulation is of great significance for practical work as engineering composite structures often contain notches and voids. In this paper, the numerical simulation of failure evolution and failure modes of carbon fiber reinforced resin composite laminates with large openings was carried out. A UMAT subroutine was written based on the 3D Hashin-Ye failure criterion and progressive damage model theory. The characteristic length and viscosity coefficient were introduced into the model to reduce mesh dependency and improve computational convergence. The nonlinear shear constitutive relationship defined by the Ramberg-Osgood equation was introduced into the continuous damage degradation model. The effect of nonlinear shear on the failure evolution of laminates with different stacking sequence was studied.

[Clinical efficacy of anterior decompression and stability reconstruction in patients with cervical hyperextension injury].

Objective: To evaluate the clinical efficacy of anterior decompression and stability reconstruction in patients with cervical hyperextension injury. Methods: Postoperative data from 60 patients with cervical hyperextension injury between April 2009 and December 2016 were analyzed retrospectively; the patients included 50 males and 10 females, aged 21-87 years [average, (57±13) years]. All patients had various degrees of spinal cord injury, and were treated with anterior cervical decompression, fusion, and internal fixation.The preoperative and postoperative neurological function were compared to evaluate the clinical efficacy of the treatment.The t test was applied when preoperative and postoperative data were compared. Results: Of the 60 patients, 5 underwent anterior cervical discectomy and fusion, 26 underwent anterior cervical corpectomy and fusion, and 29 received treatment with the hybrid technique.The average follow-up was (5.1±2.1) years (range, 1.6-9.1 years). The American Spinal Injury Association (ASIA) scores, abbreviated injury scale (AIS grades), and Japanese Orthopedic Association Scores (JOA scores) at the 1 week post operation and final follow-up were significantly better than those obtained preoperatively (all P<0.01). The JOA scores before operation and at the final follow-up was 10(7, 11) and 16(14, 17), respectively.Based on the recovery rate of JOA scores, the rate of cure was 28.3% (17 cases), the rate of significant efficiency was 60.0% (36 cases), the rate of efficiency was 8.3% (5 cases), the rate of inefficiency was 3.3% (2 cases). Among the patients showing cure, 5 were satisfied with the life function, however, the extent of their injury was still of Grade D owing to the incomplete recovery of muscle force.Further, when the 60 patients were divided into A and B groups according to whether they had congenital spinal stenosis or not, respectively, and no significant difference was found in ASIA scores, AIS grades and JOA scores between the groups (all P<0.01). Conclusion: Anterior cervical decompression, fusion and internal fixation is safe and effective for cervical hyperextension injury without continuous-type ossification of the posterior longitudinal ligament.

NMR structure of the HIV-1 nucleocapsid protein bound to stem-loop SL2 of the psi-RNA packaging signal. Implications for genome recognition.

The RNA genome of the human immunodeficiency virus type-1 (HIV-1) contains a approximately 120 nucleotide Psi-packaging signal that is recognized by the nucleocapsid (NC) domain of the Gag polyprotein during virus assembly. The Psi-site contains four stem-loops (SL1-SL4) that possess overlapping and possibly redundant functions. The present studies demonstrate that the 19 residue SL2 stem-loop binds NC with affinity (K(d)=110(+/-50) nM) similar to that observed for NC binding to SL3 (K(d)=170(+/-65) nM) and tighter than expected on the basis of earlier work, suggesting that NC-SL2 interactions probably play a direct role in the specific recognition and packaging of the full-length, unspliced genome. The structure of the NC-SL2 complex was determined by heteronuclear NMR methods using (15)N,(13)C-isotopically labeled NC protein and SL2 RNA. The N and C-terminal "zinc knuckles" (Cys-X(2)-Cys-X(4)-His-X(4)-Cys; X=variable amino acid) of HIV-1 NC bind to exposed guanosine bases G9 and G11, respectively, of the G8-G9-U10-G11 tetraloop, and residues Lys3-Lys11 of the N-terminal tail forms a 3(10) helix that packs against the proximal zinc knuckle and interacts with the RNA stem. These structural features are similar to those observed previously in the NMR structure of NC bound to SL3. Other features of the complex are substantially different. In particular, the N-terminal zinc knuckle interacts with an A-U-A base triple platform in the minor groove of the SL2 RNA stem, but binds to the major groove of SL3. In addition, the relative orientations of the N and C-terminal zinc knuckles differ in the NC-SL2 and NC-SL3 complexes, and the side-chain of Phe6 makes minor groove hydrophobic contacts with G11 in the NC-SL2 complex but does not interact with RNA in the NC-SL3 complex. Finally, the N-terminal helix of NC interacts with the phosphodiester backbone of the SL2 RNA stem mainly via electrostatic interactions, but does not bind in the major groove or make specific H-bonding contacts as observed in the NC-SL3 structure. These findings demonstrate that NC binds in an adaptive manner to SL2 and SL3 via different subsets of inter and intra-molecular interactions, and support a genome recognition/packaging mechanism that involves interactions of two or more NC domains of assembling HIV-1 Gag molecules with multiple Psi-site stem-loop packaging elements during the early stages of retrovirus assembly.

A mechanism for plus-strand transfer enhancement by the HIV-1 nucleocapsid protein during reverse transcription.

The HIV-1 nucleocapsid protein (NC) functions as a nucleic acid chaperone during the plus-strand transfer step in reverse transcription by facilitating annealing of the primer binding site (PBS) sequence in the short plus-strand strong-stop DNA fragment [(+) SSDNA] to a complementary site located near the 3' end of the minus-strand DNA [(-) PBS DNA]. To investigate the mechanism by which NC performs this function, we have prepared an 18-nucleotide (-) PBS DNA for nuclear magnetic resonance (NMR) based structural and NC binding studies. The (-) PBS DNA forms a stable hairpin (T(m) approximately 42 +/- 5 degrees C) that contains a five-residue loop and a bulged thymine in a guanosine-cytosine-rich stem. Addition of substoichiometric amounts of NC results in significant broadening and reductions in NMR signal intensities of the Watson-Crick base-paired imino protons and a reduction by 20 degrees C in the upper temperature at which the imino proton signals are detectable, consistent with destabilization of the structure. The results suggest that inefficient annealing in the absence of NC may be due to the intrinsic stability of an internal (-) PBS DNA hairpin and that NC facilitates strand transfer by destabilizing the hairpin and exposing stem nucleotides for base pairing with the PBS sequence in (+) SSDNA.

Mechanistic insights from the three-dimensional structure of 3-oxo-Delta(5)-steroid isomerase.

3-Oxo-Delta(5)-steroid isomerase (KSI) catalyzes the isomerization of beta,gamma-unsaturated 3-oxosteroids to their conjugated isomers through the formation of an intermediate dienolate. The three-dimensional structure of the enzyme from Pseudomonas testosteroni was solved by multidimensional heteronuclear magnetic resonance spectroscopy. This protein, a 28-kDa symmetric dimer, exhibits a three-dimensional fold with the two independently folded monomers packed together via extensive hydrophobic and electrostatic interactions. The previously identified catalytically important residues Tyr-14 (general acid) and Asp-38 (general base) are located near the bottom of a deep hydrophobic cavity and are positioned in a manner consistent with previous mechanistic hypotheses. The structure also revealed the presence of an unexpected acid group (Asp-99) located in the active site adjacent to Tyr-14. Mutagenesis and kinetic studies show that Asp-99 has an anomalously high pK(a) (>9), which allows it to contribute to catalysis by donating a hydrogen bond to the intermediate and to the transition states. In support of this hypothesis, effects on the kinetic parameters of the mutations Y14F and D99A are additive in the Y14F/D99A mutant.

Structure of the HIV-1 nucleocapsid protein bound to the SL3 psi-RNA recognition element.

The three-dimensional structure of the human immunodeficiency virus-type 1 (HIV-1) nucleocapsid protein (NC) bound to the SL3 stem-loop recognition element of the genomic Psi RNA packaging signal has been determined by heteronuclear magnetic resonance spectroscopy. Tight binding (dissociation constant, approximately 100 nM) is mediated by specific interactions between the amino- and carboxyl-terminal CCHC-type zinc knuckles of the NC protein and the G7 and G9 nucleotide bases, respectively, of the G6-G7-A8-G9 RNA tetraloop. A8 packs against the amino-terminal knuckle and forms a hydrogen bond with conserved Arg32, and residues Lys3 to Arg10 of NC form a 310 helix that binds to the major groove of the RNA stem and also packs against the amino-terminal zinc knuckle. The structure provides insights into the mechanism of viral genome recognition, explains extensive amino acid conservation within NC, and serves as a basis for the development of inhibitors designed to interfere with genome encapsidation.

Solution structure of 3-oxo-delta5-steroid isomerase.

The three-dimensional structure of the enzyme 3-oxo-delta5-steroid isomerase (E.C. 5.3.3.1), a 28-kilodalton symmetrical dimer, was solved by multidimensional heteronuclear magnetic resonance spectroscopy. The two independently folded monomers pack together by means of extensive hydrophobic and electrostatic interactions. Each monomer comprises three alpha helices and a six-strand mixed beta-pleated sheet arranged to form a deep hydrophobic cavity. Catalytically important residues Tyr14 (general acid) and Asp38 (general base) are located near the bottom of the cavity and positioned as expected from mechanistic hypotheses. An unexpected acid group (Asp99) is also located in the active site adjacent to Tyr14, and kinetic and binding studies of the Asp99 to Ala mutant demonstrate that Asp99 contributes to catalysis by stabilizing the intermediate.

[Preliminary experience of use of ultrasonic surgical aspirator for lung limited resection].

The authors reported 8 cases undergone lung limited resections (11 operations) by cavitron ultrasonic surgical aspirator (CUSA). There were 3 cases (6 operations) with multiple metastases in lung, 1 case with single metastasis in lung, 1 case with peripheric lung cancer, 1 case with nodule of tuberculosis in lung, 1 case with lung abscess and 1 case with lung cyst. All the patients recovered well postoperatively. Until now 4 cases with lung metastatic tumors have living well for 3.5, 1, 0.5, and 0.3 years. Ultrasonic Aspiration is very beneficial for lung limited resection: Less blood lose; Simple surgical techniques; and to be able to resect the deep lesions in lung and multiple lung lesions, and avoid lobectomy or pneumonectomy for more preserving lung tissue.

Development of a novel Bacillus subtilis cloning system employing its neutral protease as screen marker.

Part of the pUC19 polylinker sequence (33 bp) was inserted into the pro-peptide-coding region of the Bacillus subtilis neutral protease-encoding gene to replace a 93-bp FspI-HindIII fragment. This in-frame sequence replacement had little effect on the expression and secretion of the neutral protease. This plasmid can therefore be used as a cloning vector, and recombinant clones can be directly identified on skim milk indicator plates by the loss of a clear ring (or halo) around the colonies. This novel cloning system offers several advantages over existing B. subtilis cloning vectors: (i) convenient direct screening of recombinants; (ii) the use of inexpensive indicator; (iii) no restriction on the use of host strains; and (iv) the availability of seven frequently used unique cloning sites: BamHI, XbaI, SalI, PstI, SphI, HindIII, and EcoRI. This system also has the potential to be used as an expression/secretion vector.

Evidence for the covalent binding of aflatoxin B1-dichloride to cytosine in DNA.

In vitro studies of the effect of aflatoxin B1-dichloride (AFB1-Cl2) on the template function for RNA synthesis of several single- and double-stranded synthetic DNAs containing cytosine and/or hypoxanthine bases are reported. The results indicate: (i) AFB1-Cl2 strongly inhibits the template function of the single-stranded homopolymer polydC and has no effect on polydI, (ii) the inhibition is stronger when cytosine is in the double-stranded alternating copolymer poly[d(I-C)], and (iii) polydI directed RNA synthesis can be inhibited if it is in the double-stranded homopolymer polydI.polydC, although the template function of the polydC strand is still inhibited to a greater extent. The evidence that the selective inhibition of the DNA template function is a direct reflection of the binding specificities of AFB1-Cl2 is provided by the binding studies of [3H]AFB1-Cl2 to these DNAs. The binding of AFB1-Cl2 to polydC is substantiated by the dose-response template inhibition and by the dose-response template binding studies. Additionally, these results show that AFB1 per se has neither inhibitory nor binding activity. Auto radiography of [alpha-32P]GTP labeled RNAs suggests that the mechanism of inhibition of polydC template function by AFB1-Cl2 is mainly due to the inhibition of the elongation of RNA synthesis. Spectrum measurement of the products of enzyme digestion of the AFB1-Cl2 modified polydC reveals that the deoxycytidine fraction gives a typical cytosine absorption peak at 275 nm followed by a broad peak between 300 and 400 nm with a maximum at 390 nm. High performance liquid chromatography confirms the existence of a cytosine-AFB1 adduct which absorbs strongly in the regions between 250 and 400 nm with peaks identifiable at 260, 350 and 390 nm. These results strongly suggest that AFB1 in the activated form of AFB1-Cl2 is able to covalently bind to cytosine in DNA.

[The coagulogram in patients with nephrotic syndrome].

The coagulogram done in half of the 100 cases of nephrotic patients admitted into our hospital from 1986 to 1988 was studied. It is shown that the patients of either the renal vein thrombosis (RVT) positive or negative group were in hypercoagulability state. 46 patients in this series had RVT proved by renography. The mechanism of RVT and the clinical significance of the changes of these hemostatic data are discussed.

[A study on estimating the natural TB infection prevalence in BCG vaccinated regions].

The authors analysed the distribution of the sizes of tuberculin reaction of those who have not been BCG vaccinated. The result shows that the proportions of persons with certain tuberculin reactors, greater than or equal to 6mm to greater than or equal to 15mm, greater than or equal to 6mm to greater than or equal to 20mm and greater than or equal to 15mm to greater than or equal to 20mm are relatively stable. Comparing the tuberculin inoculation size in BCG vaccinated group with those of non vaccinated, it shows that the size of tuberculin reactions greater than or equal to 15mm might not be influenced by BCG vaccination. It seems that the number of reactors of greater than or equal to 15mm are able to be used to estimate the prevalence of natural TB infection in BCG vaccinated regions.

Characterization of a CO-dependent O-demethylating enzyme system from the acetogen Clostridium thermoaceticum.

An inducible O-demethylating enzyme system was characterized from Clostridium thermoaceticum cultivated at the expense of syringate. Glucose and methanol, but not CO, partially repressed its expression. Induced whole cells catalyzed the carbon monoxide (CO)-dependent O demethylation of methoxylated aromatic compounds with the concomitant formation of acetate. Pyruvate and, to a lesser extent, H2-CO2 could replace CO in these reactions. KCN inhibited pyruvate-dependent activity but not the CO-dependent activity. The ATPase inhibitor N,N'-dicyclohexylcarbodiimide, the protonophore carbonyl cyanide m-chlorophenylhydrazone, and methyl viologen did not appreciably inhibit O demethylation by induced cells, whereas Triton X-100 was inhibitory. The enzyme system appeared to convert syringate sequentially to 5-hydroxyvanillate and gallate. The proposed overall reaction stoichiometry was as follows: syringate + 2CO + 2H2O----gallate + 2 acetates. Growth-supportive methoxylated aromatic compounds were O demethylated by syringate-cultivated cells and inhibitory to syringate O demethylation.

[Epidemiologic investigation of carcinoma of the esophagus and gastric cardia carcinoma in Nanao County, Guangdong province].

Nanao county, Guangdong province is a high incidence area of carcinoma of esophagus and gastric cardia carcinoma. By retrospective investigation of data in the past 14 years (1970 to 1983), the annual average crude mortality of carcinoma of esophagus and gastric cardia carcinoma was found to be 88.65/100,000, the age adjusted mortality of Chinese population was 82.91/100,000 and that of the world population was 113.09/100,000. The mortality of the male was 100.65/100,000 and of the female was 67.24/100,000 with the ratio of 1.38:1. As regards the relationship between the age and mortality, the highest rate occurs from 50 to 74. A higher mortality was also observed in the population engaged in salt production and fishing. The mortality was higher in the lower elevation areas than in the elevated regions.