Klebsiella pneumoniae yggG Gene Product: A Zinc-Dependent Metalloprotease

Klebsiella pneumoniae causes neonatal sepsis and nosocomial infections. One of the strains, K. pneumoniae MGH 78578, shows high level of resistance to multiple microbial agents. In this study, domain family, amino acid sequence and topology analyses were performed on one of its hypothetical protein, YggG (KPN_03358). Structural bioinformatics approaches were used to predict the structure and functionality of YggG protein. The open reading frame (ORF) of yggG, which was a putative metalloprotease gene, was also cloned, expressed and characterized. The ORF was PCR amplified from K. pneumoniae MGH 78578 genomic DNA and cloned into a pET14-b vector for heterologous expression in Escherichia coli. The purified YggG protein was subsequently assayed for casein hydrolysis under different conditions. This protein was classified as peptidase M48 family and subclan gluzincin. It was predicted to contain one transmembrane domain by TMpred. Optimal protein expression was achieved by induction with 0.6 mM isopropyl thiogalactoside (IPTG) at 25 °C for six hours. YggG was purified as soluble protein and confirmed to be proteolytically active under the presence of 1.25 mM zinc acetate and showed optimum activity at 37 °C and pH 7.4. We confirmed for the first time that the yggG gene product is a zinc-dependent metalloprotease.     

Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes

Transparent, elastic conductors are essential components of electronic and optoelectronic devices that facilitate human interaction and biofeedback, such as interactive electronics, implantable medical devices and robotic systems with human-like sensing capabilities. The availability of conducting thin films with these properties could lead to the development of skin-like sensors that stretch reversibly, sense pressure (not just touch), bend into hairpin turns, integrate with collapsible, stretchable and mechanically robust displays and solar cells, and also wrap around non-planar and biological surfaces such as skin and organs, without wrinkling. We report transparent, conducting spray-deposited films of single-walled carbon nanotubes that can be rendered stretchable by applying strain along each axis, and then releasing this strain. This process produces spring-like structures in the nanotubes that accommodate strains of up to 150% and demonstrate conductivities as high as 2,200?S?cm(-1) in the stretched state. We also use the nanotube films as electrodes in arrays of transparent, stretchable capacitors, which behave as pressure and strain sensors.     

Silk fibroin-based films in food packaging applications: A review

Plastic pollution is a significant concern nowadays due to wastes generated from non-biodegradable and non-renewable synthetic materials. In particular, most plastic food packaging material ends up in landfills, creating mass wastes that clog the drainage system and pollute the ocean. Thus, studies on various biopolymers have been promoted to replace synthetic polymers in food packaging and consequently, the high number of research in biopolymers food packaging, especially in the characterization, properties and also the development of the biopolymer. For biopolymer-based food packaging, silk fibroin (SF) has been highlighted because of its biodegradability and low water vapor permeability properties. This review focuses on the different properties of SF films prepared through solution casting and electrospinning for food packaging. Discussions encompassed chemical properties, mechanical properties, permeability, and biodegradability. This review also discussed the studies that used SF as the biomaterial for food packaging.     

Determination of boric acid in foods: Comparative study of three methods

Three methods for the determination of boric acid in foods were studied in detail, namely the titrimetric method using mannitol, and two colorimetric procedures using carminic acid or curcumin. Agar-agar strips, pickled mango, noodles and prawns were analysed and the repeatability, sensitivity and recovery of the methods compared. The titrimetric and curcumin methods gave mean values for boric acid which were significantly (P < 0·05) higher than those of the carminic acid method. Results with the titrimetric method did not differ from those with the curcumin method; the latter method gave good recoveries (～ 100%) for all four foods at all levels of addition. Analyses carried out on NBS Standard Material showed that the curcumin method gave the most accurate results. This method was also found to show the least internal variation both in terms of mean boric acid content and recovery. Furthermore, the method possessed practical advantages over the other two techniques. Based on the results obtained from the comparative studies, the curcumin method was found to be the most reliable and hence would be the method of choice for boric acid determination in foods.     

Removing impurities from steel scrap using air and chlorine mixtures

The presence of zinc in steel scrap causes difficulties in the production of steel and leads to environmental problems. This article describes a separation route using air and chlorine mixtures to remove zinc from steel scrap prior to melting in an electric arc furnace. Thermodynamics shows that zinc chloride is more stable than its oxide, while the reverse is true for iron. Through the use of an air and chlorine mixture (10:1), zinc is selectively removed from steel at 800°C in the laboratory. The reaction products characterized by various analytical techniques confirm the thermodynamic analysis. This process offers an attractive solution to obtain clean steel scrap and useful chemicals. Editor’s Note: A hypertext-enhanced version of this article appears on the JOM web site at www.tms.org/pubs/journals/JOM/9908/Tee-9908.html. For more information, contact J.K.S. Tee, University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ, United Kingdom; telephone 44 (0)1223 334360; fax 44 (0)1223 334567; e-mail ksjt2@hermes.cam.ac.uk.     

Reliability assessment and hygroswelling modeling of FCBGA with no-flow underfill

In the flip-chip ball grid array (FCBGA) assembly process, no-flow underfill has the advantage over traditional capillary-flow underfill on shorter cycle time. Reliability tests are performed on both unmolded and molded FCBGA with three different types of no-flow underfill materials. The JEDEC Level-3 (JL3) moisture preconditioning, followed by reflow and pressure cooker test (PCT) is found to be a critical test for failures of underbump metallization (UBM) opening and underfill/die delamination. In this paper, various types of modeling techniques are applied to analyze the FCBGA-8×8 mm on moisture distribution, hygroswelling behavior, and thermomechanical stress. For moisture diffusion modeling, thermal-moisture analogy is used to calculate the degree of moisture saturation in the multi-material system of FCBGA. The local moisture concentration along the critical interface, e.g. die/underfill, is critical for delamination, because the moisture weakens the interfacial adhesion strength, generates internal vapor pressure during reflow, and induces tensile hygroswelling stress on UBM during PCT. The results of moisture distribution can be used as loading input for the subsequent hygroswelling modeling. The magnitude of hygroswelling stress acting on UBM is found to be greater than the thermal stress induced during reflow, both in tensile mode which may cause the UBM-opening failure. Underfill with lower saturated moisture concentration (C_sat) and coefficient of moisture expansion (CME) are found to induce lower UBM stress and has better reliability results. Molded package generally has higher stress level than unmolded package. Parametric studies are performed to study the effects of no-flow underfill materials, package type (molded vs. unmolded), die thickness, and substrate size on the stresses of UBM during reflow and PCT.     

PalmHashing: a novel approach for dual-factor authentication

Many systems require a reliable personal authentication infrastructure to recognise the identity of a claimant before granting access to him/her. Conventional secure measures include the possession of an identity card or special knowledge like password and personal identification numbers (PINs). These methods are insecure as they can be lost, forgotten and potentially be shared among a group of co-workers for a long time without change. The fact that biometric authentication is convenient and non-refutable makes it a popular approach for a personal identification system. Nevertheless, biometric methods suffer from some inherent limitations and security threats. A more practical approach is to combine two-factor or more authenticators to achieve a higher level of security. This paper proposes a novel dual-factor authenticator based on the iterated inner product between tokenised pseudo-random numbers and user-specific palmprint features. This process generates a set of user-specific compact code called PalmHash, which is highly tolerant of data offset. There is no deterministic way to get the user-specific code without having both PalmHash and the user palmprint feature. This offers strong protection against biometric fabrication. Furthermore, the proposed PalmHashing technique is able to produce zero equal error rate (EER) and yields clean separation of the genuine and imposter populations. Hence, the false acceptance rate (FAR) can be eliminated without suffering from the increased occurrence of the false rejection rate (FRR).This revised version was published online in August 2004 with corrections to the section numbers.     

Integrated vapor pressure, hygroswelling, and thermo-mechanical stress modeling of QFN package during reflow with interfacial fracture mechanics analysis

In this paper, a comprehensive and integrated package stress model is established for quad flat non-lead package with detailed considerations of effects of moisture diffusion, heat transfer, thermo-mechanical stress, hygro-mechanical stress and vapor pressure induced during reflow. The critical plastic materials, i.e., moldcompound and die attach are characterized for hygroswelling and moisture properties, which are not easily available from material suppliers. The moisture absorption during preconditioning at JEDEC Level 1, and moisture desorption at various high temperatures are characterized. The moisture diffusivity is a few orders higher at reflow temperature than moisture preconditioning temperature. Due to coefficient of moisture expansion mismatch among various materials, hygro-mechanical stress is induced. The concept is analogous to coefficient of thermal expansion mismatch which results in thermo-mechanical stress. Thermal diffusivity is much faster than the moisture diffusivity. During reflow, the internal package reaches uniform temperature within a few seconds. The vapor pressure can be calculated based on the local moisture concentration after preconditioning. Results show that the vapor pressure saturates much faster than the moisture diffusion, and a near uniform vapor pressure is reached in the package. The vapor pressure introduces additional strain of the same order as the thermal strain and hygrostrain to the package. Subsequently, the interfacial fracture mechanics model is applied to study the effect of crack length on die/mold compound and die/die attach delamination.     

Chemical and engineering approaches to enable organic field-effect transistors for electronic skin applications

Skin is the body's largest organ and is responsible for the transduction of a vast amount of information. This conformable material simultaneously collects signals from external stimuli that translate into information such as pressure, pain, and temperature. The development of an electronic material, inspired by the complexity of this organ is a tremendous, unrealized engineering challenge. However, the advent of carbon-based electronics may offer a potential solution to this long-standing problem. In this Account, we describe the use of an organic field-effect transistor (OFET) architecture to transduce mechanical and chemical stimuli into electrical signals. In developing this mimic of human skin, we thought of the sensory elements of the OFET as analogous to the various layers and constituents of skin. In this fashion, each layer of the OFET can be optimized to carry out a specific recognition function. The separation of multimodal sensing among the components of the OFET may be considered a "divide and conquer" approach, where the electronic skin (e-skin) can take advantage of the optimized chemistry and materials properties of each layer. This design of a novel microstructured gate dielectric has led to unprecedented sensitivity for tactile pressure events. Typically, pressure-sensitive components within electronic configurations have suffered from a lack of sensitivity or long mechanical relaxation times often associated with elastomeric materials. Within our method, these components are directly compatible with OFETs and have achieved the highest reported sensitivity to date. Moreover, the tactile sensors operate on a time scale comparable with human skin, making them ideal candidates for integration as synthetic skin devices. The methodology is compatible with large-scale fabrication and employs simple, commercially available elastomers. The design of materials within the semiconductor layer has led to the incorporation of selectivity and sensitivity within gas-sensing devices and has enabled stable sensor operation within aqueous media. Furthermore, careful tuning of the chemical composition of the dielectric layer has provided a means to operate the sensor in real time within an aqueous environment and without the need for encapsulation layers. The integration of such devices as electronic mimics of skin will require the incorporation of biocompatible or biodegradable components. Toward this goal, OFETs may be fabricated with >99% biodegradable components by weight, and the devices are robust and stable, even in aqueous environments. Collectively, progress to date suggests that OFETs may be integrated within a single substrate to function as an electronic mimic of human skin, which could enable a large range of sensing-related applications from novel prosthetics to robotic surgery.     

Effects of montmorillonite on the electron beam irradiated alumina trihydrate added polyethylene and ethylene vinyl acetate nanocomposite

This study aims at investigating the effects of montmorillonite (MMT) nanocomposite on the electron beam irradiated alumina trihydrate flame retardant added polyethylene and ethylene vinyl acetate blends (FRLE). The addition of MMT into FRLE blends has increased the limiting oxygen index (LOI%), which corresponds the improvement of flame resistivity, whereas increasing amount of MMT and irradiation dosage were found moderately influenced LOI% of the blends. However, incorporation of MMT has shown reinforcing effect to the FRLE, where the tensile strength for the samples subjected to 150 and 250 kGy irradiation have increased for 10.7 and 27%, respectively. In addition, increasing loading level of MMT and irradiation dosage caused inferior effects to the surface and volume resistivity of FRLE as high as four folds. This is due to the enhancement of transportability of MMT ionic in polymer matrix that caused the reduction of resistivity of FRLE. POLYM. COMPOS., 33:1883–1892, 2012. © 2012 Society of Plastics Engineers