A dynamic punch method to quantify the dynamic shear strength of brittle solids

Shear strength is an important material parameter for brittle solids. This parameter has been extensively used in material failure models. Although a few methods have been proposed to quantify this parameter under the static loading condition, there is no such a method available to measure it under dynamic loading conditions. This paper presents a punch shear device to measure the dynamic shear strength of brittle solids. In this method, a split Hopkinson pressure bar system (SHPB) is used to exert the dynamic load to a thin disc sample, which is placed in a specially designed holder to minimize the bending stress induced by punching. The sample holder also allows the punch head to load the sample directly and in combination with momentum-trap technique in SHPB, it enables soft recovery of the rock plug and rock ring produced by the punching test. The flexibility and applicability of this method is demonstrated by the application of an isotropic and fine-grained sandstone. Within the theoretical framework of the classical Mohr-Coulomb failure model, the obtained dynamic shear strengths are consistent with the dynamic tensile strengths for the same rock from the literature.

A modified Kolsky bar system for testing ultrasoft materials under intermediate strain rates

A 25 mm aluminum Kolsky bar is modified to test ultrasoft materials under intermediate strain rates (10-100 s(-1)). In this modified system, an ultralong loading pulse (5-50 ms) is generated using an 800 mm steel striker in combination with a pulse shaper made of 2.5 mm thick soft rubber. For such long loading pulses, the traditional data reduction scheme based on strain gauge measurements is not possible. We use a laser gap gauge to measure the deformation of the sample directly and monitor the low amplitude dynamic loading stresses on the sample with a pair of piezoelectric transducers that are embedded in the bars. A commercial foam rubber is tested to demonstrate the feasibility of our modified Kolsky bar system.

Mutation L437P in the 2B domain of keratin 1 causes diffuse palmoplantar keratoderma in a Chinese pedigree

Diffuse palmoplantar keratoderma (DPPK) is an autosomal dominant genodermatosis characterized by uniform hyperkeratosis of the palm and sole epidermis. This disorder can be caused by mutations in the genes keratin 1, keratin 9, keratin 16, desmoglein 1 and plakoglobin. Here we present a DPPK Chinese pedigree and identify the aetiology as a novel missense mutation, L437P, located in a highly conserved helix motif in domain 2B of KRT1. Functional analysis shows that overexpression of the L437P mutant in cultured cells leads to abnormal intermediate filament networks and filament aggregation. This gain-of-function mutation highlights the role of domain 2B in mediating filament assembly.

Semicircular bend testing with split Hopkinson pressure bar for measuring dynamic tensile strength of brittle solids

We propose and validate an indirect tensile testing method to measure the dynamic tensile strength of rocks and other brittle solids: semicircular bend (SCB) testing with a modified split Hopkinson pressure bar (SHPB) system. A strain gauge is mounted near the failure spot on the specimen to determine the rupture time. The momentum trap technique is utilized to ensure single pulse loading for postmortem examination. Tests without and with pulse shaping are conducted on rock specimens. The evolution of tensile stress at the failure spot is determined via dynamic and quasistatic finite element analyses with the dynamic loads measured from SHPB as inputs. Given properly shaped incident pulse, far-field dynamic force balance is achieved and the peak of the loading matches in time with the rupture onset of the specimen. In addition, the dynamic tensile stress history at the failure spot obtained from the full dynamic finite element analysis agrees with the quasistatic analysis. The opposite occurs for the test without pulse shaping. These results demonstrate that when the far-field dynamic force balance is satisfied, the inertial effects associated with stress wave loading are minimized and thus one can apply the simple quasistatic analysis to obtain the tensile strength in the SCB-SHPB testing. This method provides a useful and cost effective way to measure indirectly the dynamic tensile strength of rocks and other brittle materials.

Controlled multipulse loading with a stuffed striker in classical split Hopkinson pressure bar testing

Controlled multipulse loading in classical split Hopkinson pressure bar (SHPB) testing is highly desirable for investigating loading history dependent phenomena but rarely explored. Here, we present a novel technique to achieve controlled multipulse loading in SHPB testing with a stuffed striker. This stuffed striker consists of a striker tube, and a striker bar and a gap enclosed inside the tube; upon impact on the input bar, it can produce two separated loading pulses. The gap controls the delay of the second pulse with respect to the first pulse, and the pulse separation (dwell time) can be continuously tuned from zero to hundreds of microseconds. The combination of the stuffed striker and the Lindholm technique [J. Mech. Phys. Solids 12, 317 (1964)] allows for controlled multipulse loading with triple or more pulses. We have validated the working principle of this technique with experiments, and demonstrated its feasibility and flexibility for acquiring relevant dynamic data with double- and triple-pulse loading on polycrystalline Cu. This precisely controlled multipulse loading technique is readily implementable and can be applied to investigating the dynamic response of a wide range of materials.

Non-viral ex vivo transduction of human hepatocyte cells to express factor VIII using a human ribosomal DNA-targeting vector

BACKGROUND

In gene therapy, one of the most important issues is the choice of the vectors. pHrneo is a human-derived vector previously constructed by our group, which can target a foreign gene into a human ribosomal DNA (hrDNA) locus.

METHODS AND RESULTS

In this study, we inserted an expression cassette of reconstructive hFVIII (hFVIII-BDDAK39) to pHrneo to construct a targeting vector: pHrneo-BDDAK39. Through electroporation of pHrneo-BDDAK39 into HL7702 cells (human hepatocyte), we identified the homologous recombinants using polymerase chain reaction, and tested the expression of hFVIII-BDDAK39 located at the hrDNA locus. The hFVIII-BDDAK39 was successfully targeted into the hrDNA locus of HL7702 by pHrneo-BDDAK39, and the efficiency of site-specific integration was 1.1 x 10(-5). The hFVIII-BDDAK39 at the hrDNA locus of HL7702 was found to be able to express efficiently (4.3 +/- 0.9 ng 10(-6) cells 24 h(-1)).

CONCLUSION

It has been indicated that the targeting vector pHrneo-BDDAK39 can be used in gene therapy for hemophilia A.

Orientation-dependent transparency of metallic interfaces

As devices are reduced in size, interfaces start to dominate electrical transport, making it essential to be able to describe reliably how they transmit and reflect electrons. For a number of nearly perfectly lattice-matched materials, we calculate from first principles the dependence of the interface transparency on the crystal orientation. Quite remarkably, the largest anisotropy is predicted for interfaces between the prototype free-electron materials silver and aluminum, for which a massive factor of 2 difference between (111) and (001) interfaces is found.

ADME evaluation in drug discovery. 5. Correlation of Caco-2 permeation with simple molecular properties

The correlations between Caco-2 permeability (logPapp) and molecular properties have been investigated. A training set of 77 structurally diverse organic molecules was used to construct significant QSAR models for Caco-2 cell permeation. Cellular permeation was found to depend primarily upon experimental distribution coefficient (logD) at pH = 7.4, high charged polar surface area (HCPSA), and radius of gyration (rgyr). Among these three descriptors, logD may have the largest impact on diffusion through Caco-2 cell because logD shows obvious linear correlation with logPapp (r=0.703) when logD is smaller than 2.0. High polar surface area will be unfavorable to achieve good Caco-2 permeability because higher polar surface area will introduce stronger H-bonding interactions between Caco-2 cells and drugs. The comparison among HCPSA, PSA (polar surface area), and TPSA (topological polar surface area) implies that high-charged atoms may be more important to the interactions between Caco-2 cell and drugs. Besides logD and HCPSA, rgyr is also closely connected with Caco-2 permeabilities. The molecules with larger rgyr are more difficult to cross Caco-2 monolayers than those with smaller rgyr. The descriptors included in the prediction models permit the interpretation in structural terms of the passive permeability process, evidencing the main role of lipholiphicity, H-bonding, and bulk properties. Besides these three molecular descriptors, the influence of other molecular descriptors was also investigated. From the calculated results, it can be found that introducing descriptors concerned with molecular flexibility can improve the linear correlation. The resulting model with four descriptors bears good statistical significance, n = 77, r = 0.82, q = 0.79, s = 0.45, F = 35.7. The actual predictive abilities of the QSAR model were validated through an external validation test set of 23 diverse compounds. The predictions for the tested compounds are as the same accuracy as the compounds of the training set and significantly better than those predicted by using the model reported. The good predictive ability suggests that the proposed model may be a good tool for fast screening of logPapp for compound libraries or large sets of new chemical entities via combinatorial chemistry synthesis.

An improved mechanical technique for assisted hatching

BACKGROUND

Varied clinical outcomes of assisted hatching (AH) have been reported. We attempt to investigate whether the size of the zona opening created by AH is adequate for blastocyst hatching, and, if not, set up a new method to improve it.

METHODS

A new AH technique, long zona dissection (LZD), was established, and experiments were performed to compare the effects of different sizes of zona opening on complete hatching of blastocysts in mouse and human embryos in vitro.

RESULTS

The LZD technique can create a long zona slit on early embryos, even blastocysts, with the slit size beyond two-thirds of zona diameter. Compared with three-dimensional partial zona dissection, LZD can significantly enhance the hatching speed and the rate of complete hatching of mouse blastocysts (93.9%). All (100%) human blastocysts completely hatched following LZD; however, when the slit size after AH was about two-fifths of zona diameter, more of the larger inner cell masses (ICM) became trapped by the zona opening during hatching than the smaller ICM (53.3 versus 12.5%, P = 0.01).

CONCLUSIONS

Zona opening of moderate size following AH is inadequate for the completion of blastocyst hatching in vitro; in some cases, however, it can be significantly improved by LZD.

Confirmation and refinement of a genetic locus for disseminated superficial actinic porokeratosis (DSAP1) at 12q23.2-24.1

BACKGROUND

Our previous study has identified two loci for disseminated superficial actinic porokeratosis (DSAP), but the genes responsible are still unknown.

OBJECTIVES

To narrow down the candidate regions and to assess candidate genes.

METHODS

A genome-wide scan and linkage analysis were carried out in a newly collected five-generation Chinese family with DSAP. In addition, six candidate genes were screened for possible DSAP-associated mutations.

RESULTS

DSAP in this family was associated with chromosome 12q. Fine mapping and haplotype construction refined the DSAP1 locus to a 4.4-cM interval. No disease-associated mutation was detected in CRY1, C4ST1, TXNRD1, HCF2, CMKLR1 or KIAA0789 genes.

CONCLUSIONS

The DSAP1 locus was localized to a 4.4-cM interval at chromosome 12q23.2-24.1. CRY1, C4ST1, TXNRD1, HCF2, CMKLR1 and KIAA0789 genes were not associated with DSAP1.

ADME Evaluation in Drug Discovery. 4. Prediction of Aqueous Solubility Based on Atom Contribution Approach

A novel method for the estimation of aqueous solubility was solely based on simple atom contribution. Each atom in a molecule has its own contribution to aqueous solubility and was developed. Altogether 76 atom types were used to classify atoms with different chemical environments. Moreover, two correction factors, including hydrophobic carbon and square of molecular weight, were used to account for the inter-/intramolecular hydrophobic interactions and bulkiness effect. The contribution coefficients of different atom types and correction factors were generated based on a multiple linear regression using a learning set consisting of 1290 organic compounds. The obtained linear regression model possesses good statistical significance with an overall correlation coefficient (r) of 0.96, a standard deviation (s) of 0.61, and an unsigned mean error (UME) of 0.48. The actual prediction potential of the model was validated through an external test set with 21 pharmaceutically and environmentally interesting compounds. For the test set, a predictive r=0.94, s=0.84, and UME=0.52 were achieved. Comparisons among eight procedures of solubility calculation for those 21 molecules demonstrate that our model bears very good accuracy and is comparable to or even better than most reported techniques based on molecular descriptors. Moreover, we compared the performance of our model to a test set of 120 molecules with a popular group contribution method developed by Klopman et al. For this test set, our model gives a very effective prediction (r=0.96, s=0.79, UME=0.57), which is obviously superior to the predicted results (r=0.96, s=0.84, UME=0.70) given by the Klopman's group contribution approach. Because of the adoption of atoms as the basic units, our addition model does not contain a "missing fragment" problem and thus may be more simple and universal than the group contribution models and can give predictions for any organic molecules. A program, drug-LOGS, had been developed to identify the occurrence of atom types and estimate the aqueous solubility of a molecule.

Spin-dependent transparency of ferromagnet/superconductor interfaces

We combine parameter-free calculations of the transmission and reflection matrices for clean and dirty interfaces with a scattering-theory formulation of Andreev reflection (AR) generalized to spin-polarized systems in order to critically evaluate the use of an extended Blonder-Tinkham-Klapwijk (BTK) model to extract values of the spin polarization for ferromagnetic metals from measurements of point-contact AR. Excellent agreement with the experimental conductance data is found for Pb/Cu but it is less good for Pb/Ni and poor for Pb/Co, indicating that the BTK formalism does not describe transport through superconducting/ferromagnetic interfaces correctly.

A novel locus (DSAP2) for disseminated superficial actinic porokeratosis maps to chromosome 15q25.1-26.1

BACKGROUND

Disseminated superficial actinic porokeratosis (DSAP) is a chronic cutaneous disorder characterized by multiple superficial keratotic lesions surrounded by a slightly raised keratotic border. It develops in teenagers in sun-exposed areas of skin and usually follows an autosomal dominant inheritance pattern. The first locus for DSAP was localized to chromosome 12q23.2-24.1, but no gene responsible for porokeratosis has been identified to date.

OBJECTIVES

To determine whether DSAP is a genetically heterogeneous disorder and to identify the disease gene locus in a three-generation Chinese family with DSAP.

METHODS

Genetic linkage analysis was carried out in this family using 15 microsatellite markers between D12S1671 and D12S369 on chromosome 12q, followed by a genome-wide scan with 382 microsatellite markers from the autosomes.

RESULTS

Genetic linkage analysis with chromosome 12q markers suggested that the locus in this family is not linked to chromosome 12q. A genome-wide scan and fine mapping finally localized the locus for DSAP in this family to a 6.4-cM region between markers D15S1023 and D15S1030 at chromosome 15q25.1-26.1. This DSAP locus was named DSAP2.

CONCLUSIONS

The previous results and this study have shown that DSAP is a genetically heterogeneous disorder; a novel locus for DSAP, termed DSAP2, was mapped to a 6.4-cM region between markers D15S1023 and D15S1030.

Association of ethylene dibromide (EDB) with mature cranberry (Vaccinium macrocarpon) fruit

Ethylene dibromide (EDB), a potential carcinogen, has been used in gasoline mixtures to avoid the accumulation of metallic lead in engines. Ethylene dibromide is present in the environment and in groundwater. Previous analysis has shown that EDB levels have reached up to 16 microg L-1 in the groundwater at two fuel spill plumes in the vicinity of the Massachusetts Military Reservation (MMR) Base and up to 1.69 microg L-1 in the Coonamessett and Quashnet Rivers in Cape Cod, MA (U.S. Air Force IRP, Fact Sheet #98-10, 1998). Groundwater and river water from this area are used to flood some local cranberry bogs for irrigation and harvesting of cranberry fruits. The potential sorption of EDB by cranberry fruits during harvest has caused concern but information regarding its occurrence is not available. In this study, low levels of EDB (0.04-0.15 microg kg-1) were found to be associated with cranberry fruits that were exposed to EDB at levels ranging from 3 to 12 microg L-1 at 10, 20, and 30 degrees C for up to 7 days. Rinsing EDB-exposed cranberry fruits twice with deionized water or once with 0.01 M NaCl solution reduced the amount of EDB associated with the cranberry fruits by 65-72% to a level of 0.02 microg kg-1. Therefore, the EDB most likely is associated with the water residue on the surface of the cranberry fruit rather than being absorbed into the flesh of the fruit during the EDB exposure.

[Mutation characteristic of STK]

OBJECTIVE

To identify the mutation characteristic of STK(11) gene in Chinese with Peutz-Jeghers syndrome(PJS) and establish the base of the gene diagnosis of PJS.

METHODS

STK(11) germline mutation was analysed by DNA sequencing in 18 unrelation patients with PJS.

RESULTS

Six novel mutations of STK (11) gene were detected in six unrelation patients. These mutations will lead to production of truncated protein.

CONCLUSION

STK (11) gene mutation accounts for one third of the Chinese with PJS. The content of mutation includes single base substitution or deletion and one or two bases insertion. The mutations were widely found in different regions of the whole coding sequence, and 2/3 of those concentr ate in exon 1. Mutation frequency is 66.7% in the family suffering PJS in two or more generations, and 16.7% in the disseminated cases.

Identification of a locus for disseminated superficial actinic porokeratosis at chromosome 12q23.2-24.1

Disseminated superficial actinic porokeratosis is an autosomal dominant cutaneous disorder characterized by many uniformly small, minimal, annular, anhidrotic, and keratotic lesions. The genetic basis for this disease is unknown. Using a genomewide search in a large Chinese family, we identified a locus at chromosome 12q23.2-24. 1 responsible for disseminated superficial actinic porokeratosis. The fine mapping study indicates that the disseminated superficial actinic porokeratosis gene is located within a 9.6 cM region between markers D12S1727 and D12S1605, with a maximum two-point LOD score of 20.53 (theta = 0.00) at D12S78. This is the first locus identified for a genetic disease where the major phenotype is porokeratosis. The study provides a map location for isolation of a gene causing disseminated superficial actinic porokeratosis.

[The influence of some factors on DNA cycle sequencing]

OBJECTIVE

To study the influence of some factors on DNA cycle sequencing.

METHODS

The effects of DNA templates, primers, cycle sequencing reaction conditions as well as purification methods were comparatively analyzed.

RESULTS

When the DNA concentration was low, the nucleotide curve showed low ratio of signal to noise, even there were no fluorescent signal. While DNA concentration was too high, the readable length of nucleotides was short. Ions in the DNA template could result in bad sequencing reaction. The Tm value, length and G+C content of primers had no obvious influences on sequencing reaction. The alteration of the denaturing, annealing and extension temperature, or the addition of dimethl sulfoxide or glycerin facilitated sequencing some DNA templates. The fluorescent residues in the purified products of the sequence reaction could interfere the automatic reading of the sequencer, but did not influence the manually proofreading of the sequence.

CONCLUSION

The purity and concentration of DNA templates are closely related to sequence data quality. The modification of reaction parameters and usage of additives can help to obtain good result of sequencing some DNA with certain structure. The use of 70% ethanol is recommended to precipitate the extension product.