bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal Thermal Management of IBM P-Server Large Format Multi-Chip Modules Utilizing Small Gap Technology
Authors: Coico Patrick A. , Messina Gaetano , Ostrander Steven , Zitz Jeffrey , Zou Wei
Published: April 2009

The large Multi-Chip Modules (MCM) used in the IBM p-Server computer systems, and their predecessors, have required rather unique cooling solutions and module hardware designs in order to meet the thermal, mechanical and reliability requirements placed on the package. The module internal thermal solution has evolved from a spring-loaded metal contact technology to a thermal compound based design using a novel gap adjustment technology employing a soldered conduction component. This current MCM makes use of a novel technology called Small Gap Technology (SGT). This technique makes it possible to control thermal compound interface thicknesses or gaps to a very tight tolerance from chip-to-chip and module-to-module. Heat flux values that have been handled vary from approximately 20 to 53 W/cm2 depending on the type of chip and the system performance level. Even higher heat fluxes have been projected for next generation products. The hardware and processing techniques employed to manufacture these modules are quite unique. These products are typically on the order of 100mm chip carrier size or 140mm overall module footprint on a side (approximately 90 cm2 of carrier area) and contain 8 chips and numerous discrete devices. The process fixturing and equipment must be able to handle the relatively large thermal mass of the components. The sequence of processing steps must take into account limitations on the material properties of the various module components. This paper will describe the SGT thermal management solution. The hardware and process employed to make the gap adjustments and the thermal interface material used in these high heat flux applications will be discussed. In addition, supporting thermal/mechanical modelling, thermal performance data and reliability data will be presented.
Mapping Potential Heatsink Conductance Across the Hydraulic Plane
Authors: Holahan Maurice F.
Published: April 2009

A systematic examination of parallel plate fin heat sink performance is carried out by means of a parametric study focussed on aluminum and copper fins in air. The objective is to find the maximum available fin conductance of fixed fin volumes as a function of hydraulic operating point. The fin pitch, height, flow length, and thickness/gap solidity are all varied. Peak volumetric conductance fin geometries are established using a search algorithm. The results are presented as a continuous mapping of peak-enabling fin geometry across the flow-pressure hydraulic operating plane. A correlation is presented showing how the peak conductance varies with pressure, fin volume, and material conductivity.
Leading Indicators of Failure for Prognostication of Leaded and Lead-Free Electronics in Harsh Environments
Authors: Lall Pradeep , Islam Nokibul , Choudhary Prakriti , Suhling Jeff
Published: April 2009

In this paper, a methodology for prognostication-of-electronics has been developed for accurate assessment of residual life in a deployed electronic components, and determination of damage-state in absence of macro-indicators of failure. Proxies for leading indicators-of-failure have been identified and correlated with damage progression under thermomechanical loads. Examples of proxies include — microstructural evolution characterized by average phase size and intermetallic growth rate in solder interconnects. Validity of damage proxies has been investigated for both 63Sn37Pb leaded and SnAgCu leadfree electronics. Structures examined include — plastic ball grid array format electronic and MEMS Packages and discrete devices assembled with FR4-06 laminates. Focus of the research presented in this paper is on interrogation of the aged material’s damage state and enhancing the understanding of damage progression. The research is aimed at development of damage relationships for determination of residual life of aged electronics and assessment of design margins instead of life prediction of new components. The prognostic indicators presented in this paper, can be used for health monitoring of electronic assemblies.
Development of a New Microscopic Four-Point AFM Probe for the Measurement of Local Electrical Conductivity
Authors: Ju Bing-Feng , Ju Yang , Saka Masumi
Published: April 2009

A microscopic four-point atomic force microscope (AFM) probe with concomitant experimental technique for local conductivity measurement is presented. A silicon nitride based AFM contact-mode probe with a V-shaped tip, which patterned by using the conventional photolithography method, is selected. The probe is then etched to four parallel isolated electrodes for the purpose of performing current input and electrical potential drop measurement. The new probe not only inherits the function of surface topography generating but also has the capability of characterizing the local conductivity simultaneously. The nanoresolution position control mechanism of AFM allows the probe scanning across micrometers sized area and creating high spatial resolution map of the in-plane conductivities. Experiments have shown the microscopic four-point probe to be mechanically flexible and robust. The repeatable conductivity measurements on the surface of aluminum and indium tin oxide (ITO) thin films indicate the technique has potential application for characterizing the devices and materials in microscale.
Surface Activated Flip-Chip Bonding of Laser Chips
Authors: Higurashi Eiji , Nakagawa Masao , Suga Tadatomo , Sawada Renshi
Published: April 2009

This paper reports the results of low-temperature flip-chip bonding of a vertical cavity surface emitting laser (VCSEL) on a micromachined Si substrate. Low temperature bonding was achieved by introducing the surface activation by plasma irradiation into the flip-chip bonding process. After the surfaces of the Au electrodes of the VCSEL and Si substrate were cleaned using an Ar radio frequency (RF) plasma, Au-Au bonding was carried out only by contact in ambient air with applied static pressure. At a bonding temperature of 100°C, the die-shear strength exceeded the failure criteria of MIL-STD-883.
Thermal Characterization and Modeling of Stacked Die Packages
Authors: Szabo P. , Rencz M. , Sze´kely V. , Poppe A. , Farkas G. , Courtois B.
Published: April 2009

The main issues in the thermal characterization and modeling of stacked die packages are the appropriate model generation, and the qualification of the die attach quality between the different layers of the stacked die structures. The first part of the paper gives a short introduction of stacked die packages. The next chapter describes the main issues of steady state and transient compact model generation for the thermal behavior of stacked die packages. The third large part of the paper gives an overview of the different methodologies applied today for the quality characterization of the different die attach layers, as a major indicator of the reliability of the package.
Development of a Hermetically Sealed Enclosure for MEMS in Chip-on-Flex Modules Using Liquid Crystalline Polymer (LCP)
Authors: Chen Morgan , Evers Nicole , Kapusta Chris , Iannotti Joe , Pham Anh-Vu , Kornrumpf William , Maciel John , Karabudak Nafiz
Published: April 2009

We present the development of a hermetic shield packaging enclosure for RF microelectromechanical system switches (MEMS) using Liquid Crystal Polymer (LCP). A cavity formed in LCP has been laminated, at low temperature, onto a Si MEMS switch to create a hermetically sealed package. The hermetically sealed enclosure is a stack-up layer of the multi-layer organic chip-on-flex system-on-a-package (SOP). The entire SOP hermetically sealed package has a total insertion loss of ∼0.5 dB at X-band. E595 outgas tests demonstrate that the LCP package is reliable and hermetically protects the MEMS switch.
Variable Focal Length Microlens by Low Voltage Electrowetting on Dielectric (EWOD) Actuation
Authors: Dash Raj K. , Borca-Tasciuc Theodorian
Published: April 2009

This work presents a design and proposed microfabrication steps for a two-liquid variable focal length capillary microlens. The capillary lens is actuated by electrowetting on dielectric effect. The microlens is made from a dielectric liquid whereas a conducting liquid serves as one of the electrodes for the actuation. The dependence of the microlens focal length on the properties of the dielectric materials is investigated using a model for electrowetting on dielectric effect. The model indicates that low voltage actuation (<20V) is possible by adjusting the dielectric layer thickness. The effect of the microlens size on the focal length is presented. The advantages of a two-liquid capillary microlens are briefly discussed.
Liquid Crystal Polymer for RF MEMS Packaging
Authors: Faheem Faheem F. , Lee Y. C.
Published: April 2009

We have developed a liquid crystal polymer (LCP) encapsulation technology for RF MEMS. The RF MEMS devices are flip-chip interconnected with other circuit elements on an alumina substrate. After flip-chip device transfer, LCP is used to encapsulate the device on the substrate. This approach is similar to glob-top encapsulation used for low-cost microelectronic packaging. The effectiveness of LCP (Vectra A950) sealing has been demonstrated by monitoring the moisture level inside the package under a 100% RH environment. In addition, the LCP’s permeabilities to helium and nitrogen were measured through a standard membrane characterization setup. These permeabilities were proven to be in the same level as those of glasses used for hermetic sealing. LCP is an excellent encapsulation material for hermetic or near-hermetic packaging of RF MEMS.
Testing the Thermal Resistance and Power Capacity of Production Heat Pipes
Authors: Kang Sukhvinder , Cook Randy , Gailus Dave
Published: April 2009

In recent years heat pipes have become widely use in high performance air-cooled heat sinks for cooling electronics equipment. Such heat sinks rely on the heat pipes to collect heat from small high heat flux sources, transport it over some distance, and spread the heat efficiently to a volume of fins where the heat is transferred to an air flow stream by convection. When used effectively, heat pipes enable heat sinks that have low thermal resistance and low mass. For the heat sink to be successful, the heat pipes must also have sufficient heat transport capacity. To deliver their design thermal resistance and heat transport capacity, heat pipes need to be manufactured with well-controlled wick characteristics, working fluid fill volume and minimal residual non-condensable gases. It is standard procedure for heat pipe manufacturing companies to test 100 percent of the heat pipes they manufacture. The most commonly used production test is designed to rapidly show whether or not a heat pipe functions as a heat pipe. On a sampling basis, manufacturers also test the heat transport capacity of their heat pipes. There is no rapid test that can verify that any specific heat pipe will achieve the desired operational life — this is achieved by validation of the manufacturing process and adequate manufacturing process controls. In this paper we describe a test method and apparatus that can be used to rapidly test whether a heat pipe has the required thermal resistance at the specified heat transport capacity. The apparatus is capable of testing heat pipes over a wide range of diameters and lengths in their end use configuration (with bends and flattened regions). The key design criteria for the test apparatus is described and test data for several application specific heat pipes is presented.
Thermal Management of Voids and Delamination in TIMs
Authors: Gektin Vadim
Published: April 2009

The paper parametrically assesses the impact of the voids/delamination on the system thermal performance. Analysis are carried out numerically and validated against experimental data (thermal measurements and C-SAM images). Topics covered include the relationship between voids/delamination and TIMs’ and heat spreader’s effective thermal conductivity; sensitivity of the system thermal performance to void/delamination size and location; voids/delamination impact vs. on the chip power dissipation (uniform vs. non-uniform); comparison of TIM1 vs. TIM2 voids impact; and, finally, comparison of voids vs. delamination.
Multi-Layer Thermionic-Tunneling Structures for Power Generation
Authors: Zeng Taofang
Published: April 2009

A new method for power generation based on nano-engineered interface design with partially filled gap is proposed. The device combines electron thermionic emission and tunneling to enhance electron transport. Thermal radiation and tunneling contribute to heat transfer in the device, which can be minimized using selected materials. The largely reduced heat transfer coupled with use of multi-layer structures enable a substantial temperature difference between heat source and heat sink or two electrodes, thereby maximizing heat source utilization. Detailed analyses are provided for the solid device operating either as a power generator or as a cooler.
Modeling of Thermo-Mechanical Stresses in Copper Interconnect/Low-k Dielectric Systems
Authors: Shen Y.-L.
Published: April 2009

Systematic finite element analyses are carried out to model the thermomechanical stresses in on-chip copper interconnect systems. Constitutive behavior of encapsulated copper films, determined by experimentally measuring the stress-temperature response during thermal cycling, is used in the model for predicting stresses in copper interconnect/low-k dielectric structures. Various combinations of oxide and polymer-based low-k dielectric schemes are considered. The evolution of stresses and deformation pattern in the dual-damascene copper, barrier layers, and the dielectrics is seen to have direct connections to the structural integrity of contemporary and future-generation devices. In particular, stresses experienced by the thin barrier layers and the mechanically weak low-k dielectrics are critically assessed. A parametric analysis on the influence of low-k material properties is also conducted. Practical implications in reliability issues such as voiding, interface fracture, electromigration and dielectric failure are discussed.
Evaluation of Spiral Inductors Embedded in Low Temperature Co-Fired Ceramic Substrates
Authors: Choi Woon , Ono Shintaro , Yoshida Seiichiro , Tomokage Hajime
Published: April 2009

In order to obtain full information on the high frequency performance of embedded passive elements, we design test elements group (TEG) substrates and compare the simulation result with measured data. S-parameters of spiral inductors embedded in low temperature co-fired ceramic (LTCC) substrates are simulated using high frequency structure simulator (HFSS), microwave studio (MWS) and advanced design simulator (ADS). Then effective inductance and Q factors are calculated from S-parameters after de-embedding process. Measurements of S-parameters are performed using a vector network analyzer in the frequency range up to 15 GHz. The simulation result with dimensional data measured by laser microscope and X-lay microscope is in good agreement with the experimental result. It is suggested that the simulation results can be applied to the design of system-in-a-package (SiP) substrate directly without making TEG.
CO2 Laser Drilling of Microvias Using Diffractive Optics Techniques: I — Mathematical Modeling
Authors: Zhang Chong , Bet Sachin , Salama Islam A. , Quick Nathaniel R. , Kar Aravinda
Published: April 2009

This paper is the first of three parts summarizing the research to use diffractive optics at the CO2 laser wavelength to drill microvias in the 40–50 μm range for organic packaging applications. This first part mainly focuses on mathematical modeling of the drilling process, which is used to define the characteristics of the laser beam necessary to achieve the required geometry of the microvias. These laser characteristics and the properties of the incoming laser beam of the CO2 laser system are then used to provide a deterministic approach for obtaining performance data for the diffractive optics design. The targeted optics are designed based on the modeling result and are then integrated into a prototype system to execute the drilling operation. The model is based on the conversion of optical energy into thermal energy due to laser-substrate interaction, propagation of thermal energy in the substrate, thermal as well as radiation damage threshold of the substrate and other important laser drilling parameters (e.g., fluence, temporal and spatial characteristics of the beam, residue at the via bottom).
Characterization of Fine Pitch CSP Solder Joints Under Board-Level Free Fall Drop (BFFD)
Authors: Xie Dongji , Geiger David , Shangguan Dongkai , Rooney Daniel T. , Gullo Louis J.
Published: April 2009

This paper presented a board-level free fall drop (BFFD) to simulate product free fall drop (PFFD). In BFFD, the board structure is very close to the actual cellular phone boards with similar size. The board edges were reinforced by metal frame and screws similar to the cellular phone housing. The drop test was performed to characterize the solder joints of 0.4mm pitch chip scale package (CSP) packages. To charaterize the stress level, the acceleration was measured and the free drop test was performed for more than 140 boards with different CSP structures. The plastic strain of solder joints in different location was calculated using finite element analysis (FEA). It was found that the strain level is both location and component dependent. This strain level will determine the probability of drop test failure in terms of number of drops to failure. The impact of component type, body size and component location was investigated by both experimentally and FEA. Through drop test, the number of drop before failure (MDBF) were recorded and compared across various CSPs. Failure analysis was also performed to confirm the failure modes.
On Hermeticity Detection of Wafer Level Packages for MEMS Devices
Authors: Goswami A. , Han B. , Wade C. , Chien A.
Published: April 2009

Wafer level packaging has emerged as one of the promising solutions for hermetic packaging of MEMS devices. Detection of the level of hermeticity of the package is essential for reliability and design assessment of the devices. Traditionally, hermeticity has been tested using Helium based fine leak testing. However, there are limitations when this technique is used for the hermeticity detection of small volumes (< 10−3 cc) that are typical in wafer level packages. This paper reviews the helium fine leak test, its limitations and the influence of the different test parameters on leakage rate measurement are analyzed for wafer level packages with small cavity volumes. The results indicate a need for development of a new hermeticity measurement technique to achieve the measurement sensitivity required for wafer level packages.
Surface Micromachined Microfluidics: Example Microsystems, Challenges and Opportunities
Authors: Galambos Paul , James Conrad
Published: April 2009

A variety of fabrication techniques have been used to make microfluidic microsystems: bulk etching in silicon and glass, plastic molding and machining, and PDMS (silicone) casting. Surprisingly the most widely used method of integrated circuit (IC) fabrication (surface micromachining — SMM) has not been extensively utilized in microfluidics despite its wide use in MEMS. There are economic reasons that SMM is not often used in microfluidics; high infrastructure and start-up costs and relatively long fabrication times: and there are technical reasons; packaging difficulties, dominance of surface forces, and fluid volume scaling issues. However, there are also important technical and economic advantages for SMM microfluidics relating to large-scale batch, no-assembly fabrication, and intimate integration of mechanical, electrical, microfluidic, and nano-scale sub-systems on one chip. In our work at Sandia National Laboratories MDL (Microelectronics Development Lab) we have built on the existing MEMS SMM infrastructure to produce a variety of microfluidic microsystems. These example microsystems illustrate the challenges and opportunities associated with SMM microfluidics. In this paper we briefly discuss two SMM microfluidic microsystems (made in the SUMMiT™ and SwIFT™ processes — www.mdl.sandia.gov/micromachine) in terms of technical challenges and unique SMM microfluidics opportunities. The two example microsystems are a DEP (dielectrophoretic) trap, and a drop ejector patterning system.
A Fracture Mechanics Analysis of Underfill Delamination in Flip Chip Packages
Authors: Mahalingam Saketh , Tonapi Sandeep , Sitaraman Suresh K.
Published: April 2009

Flip chip technology offers a number of advantages over conventional packaging techniques such as smaller size and efficient high-speed signal transmission. However, when assembled on organic substrates, the flip chip needs to be underfilled with a suitable adhesive to enhance the thermo-mechanical reliability of its solder bumps. When such flip chip assemblies are subjected to thermal excursions, the underfill material may delaminate resulting in premature solder bump fatigue failure. Available open literature has extensively focused on underfill delamination propagation due to monotonic loading conditions. However, the information on underfill fatigue delamination propagation is limited. This paper presents an experimental and modeling study on the underfill delamination under monotonic as well as fatigue loading conditions. In this work, the fracture toughness of the passivation-underfill interface has been characterized using the single leg bending test. In addition, a fatigue delamination propagation experiment has been done, and a Paris law type model for delamination propagation has been developed. In parallel, numerical models have been developed to determine the available energy release rate under monotonic loading conditions as well as the range of energy release rate range under thermal cycling conditions. The mode mixity calculations have been carried out using Crack Surface Displacement (CSD) method. Using the models and the experimental data, guidelines against the delamination of the underfill material are developed.
Single-Strip Decohesion Test to Characterize Nano-Scale Thin Film Delamination
Authors: Zheng Jiantao , Sitaraman Suresh K.
Published: April 2009

A new test method, Single-Strip Decohesion Test (SSDT), has been developed and used to measure the interfacial fracture toughness of nano-scale thin film on substrate. This fixtureless test employs a stress-engineered superlayer deposited on patterned titanium (Ti) film strips to supply the energy for the delamination from a thick silicon (Si) substrate. The amount of energy available for delamination propagation is varied by fabricating an etchable thin release layer of varying width between the film strips and the substrate. By designing a decreasing area of the release layer, it is possible to arrest the delamination at a given location, and the interfacial fracture toughness or critical energy release rate can be found at the location where the delamination ceases to propagate. Common IC fabrication techniques are used to prepare the sample and execute the test, thereby making the test compatible with current microelectronic or MEMS facilities and suitable for in process measurement of thin film adhesion strength. The methodology presented in this paper is generic in nature, and can be used to measure the process-dependent interfacial fracture toughness of various micro-scale and nano-scale thin film interfaces. Ti thin film with thickness ranging from 5nm to 100nm can be studied using this method.
Multilayer Direct-Writing of Electrical Conductors With Gold Nanoinks Using the Fountain-Pen Principle
Authors: Dockendorf Ce´dric P. R. , Choi Tae-Youl , Poulikakos Dimos , Grigoropoulos C. P.
Published: April 2009

Previous publications showed the potential of gold nanoparticle inks in microelectronic manufacturing. The main advantage of using nanoparticles for the production of microelectronic conductors is their low melting point. Indeed the melting point of gold nanoparticles decreases dramatically with decreasing size. This interesting property presents us with an uncomplicated way in which to produce electronic conductors on plastics, thus manufacture flexible electronics. Microelectronic applications which make use of materials other than silicon make their appearance ever more often. In this paper we present a method of manufacturing multilayered electronic circuits using a scanning-probe-inspired technology to deposit and anneal a gold nanoink on various substrates. We then tested the quality of this technology by applying it to a real complete electronic circuit.
Experimental Investigation of the Miniature Loop Heat Pipe With Flat Evaporator
Authors: Singh Randeep , Akbarzadeh Aliakbar , Mochizuki Masataka , Nguyen Thang , Wuttijumnong Vijit
Published: April 2009

Loop heat pipe (LHP) is a very versatile heat transfer device that uses capillary forces developed in the wick structure and latent heat of evaporation of the working fluid to carry high heat loads over considerable distances. Robust behaviour and temperature control capabilities of this device has enable it to score an edge over the traditional heat pipes. In the past, LHPs has been invariably assessed for electronic cooling at large scale. As the size of the thermal footprint and available space is going down drastically, miniature size of the LHP has to be developed. In this paper, results of the investigation on the miniature LHP (mLHP) for thermal control of electronic devices with heat dissipation capacity of up to 70 W have been discussed. Copper mLHP with disk-shaped flat evaporator 30 mm in diameter and 10 mm thickness was developed. Flat evaporators are easy to attach to the heat source without any need of cylinder-plane-reducer saddle that creates additional thermal resistance in the case of cylindrical evaporators. Wick structure made from sintered nickel powder with pore size of 3–5 μm was able to provide adequate capillary forces for the continuos circulation of the working fluid, and successfully transport heat load at the required distance of 60 mm. Heat was transferred using 3 mm ID copper tube with vapour and liquid lines of 60 mm and 200 mm length respectively. mLHP showed very reliable start up at different heat loads and was able to achieve steady state without any symptoms of wick dry-out. Tests were conducted on the mLHP with evaporator and condenser at the same level. Total thermal resistance, R total of the mLHP came out to be in the range of 1–4°C/W. It is concluded from the outcomes of the investigation that mLHP with flat evaporator can be effectively used for the thermal control of the electronic equipments with restricted space and high heat flux chipsets.
Integrated Passives for Commercial Wireless Applications (Invited Paper)
Authors: Henderson Rashaunda M. , Petras Michael F.
Published: April 2009

This paper discusses the modeling, design and performance of inductors and capacitors fabricated in high density interconnect (HDI), low temperature co-fired ceramic (LTCC) and silicon (Si) integrated circuit technologies. Scalable models demonstrate the capability of designing LC-based resonators and filters for use in cellular front-end modules. The performance of the circuits is presented along with size comparisons.
SOP Embedded Thin Film Resistors on High and Low Loss Thin Film Dielectrics
Authors: Bhattacharya Swapan , Varadarajan Mahesh , Chahal Premjeet , Lee K. J. , Bhattacharjee Ajanta , Tummala Rao R. , Sitaraman Suresh , Papapolymerou John , Tentzeris Manos , Laskar Joy
Published: April 2009

This paper describes low-cost materials and processes for embedded thin film resistors that can be integrated into printed wiring board using sequential build-up processes. Realization of embedded resistors on conventional board level high loss epoxy (∼0.015 at 1 GHz) and proposed low loss BCB dielectric (∼0.0008 at > 40 GHz) has been explored in this study. Foil transfer and electroless plating have been attempted for embedding thin film resistors. Ni-P alloys were plated using conventional electroless plating, and NiCr and NiCrAlSi foils were used for the foil transfer process. A test vehicle consisting of various geometry and values of resistors was designed and fabricated to evaluate electrical and mechanical reliability of embedded thin film resistors. For the first time, Benzocyclobutene (BCB) has been proposed as a board level dielectric for advanced System-on-Package (SOP) module primarily due to its attractive low-loss (for RF application) and thin film (for high density wiring) properties. To realize embedded resistors on multi-layer BCB, a low-cost large format electroless process for deposition of NiP and NiWP thin film resistors using both low- (25°C) and high-temperature (90°C) baths has been developed. The electroless process exhibits uniform resistor thickness in the sub-micron range and offers low profile and excellent adhesion to BCB dielectric. These films also act as a seed layer for the subsequent direct electroplating of copper traces. NiP alloys can also be tailored to variable temperature coefficient of resistance (TCR) with different alloy compositions. The electroless process can be adopted in the PCB manufacturing industries with no additional investment.
Extinction-Reconsolidation Boundaries: Key to Persistent Attenuation of Fear Memories
Authors: Monfils Marie-H. , Cowansage Kiriana K. , Klann Eric , LeDoux Joseph E.
Published: April 2009

Reversing Pavlov

Memories of fearful associations, such as hearing a tone before receiving a low-voltage shock, are labile when they are retrieved, such that the association can be extinguished or reconsolidated.

Monfils
et al.

(p.
951
, published online 2 April) demonstrate that applying a standard extinction treatment (sounding the tone multiple times in the absence of any shocks) within a window of time during which reconsolidation would normally occur has the effect of overwriting the original memory. Rats treated in this fashion display much lower levels of renewal (fear induced by sounding the tone once by itself), reinstatement (fear induced by giving the shock once by itself), and spontaneous recovery.
Size and Shape of Saturn's Moon Titan
Authors: Zebker Howard A. , Stiles Bryan , Hensley Scott , Lorenz Ralph , Kirk Randolph L. , Lunine Jonathan
Published: April 2009

Global Analysis of Titan

In its orbit around Saturn, the Cassini spacecraft passes regularly by the planet's largest moon, Titan. Using a radar instrument to peer through the moon's thick atmosphere,

Zebker
et al.

(p.
921
, published online 2 April) developed a global model of Titan. Titan is slightly oblate, so that its poles have lower elevations than the equator, which may explain why the moon's hydrocarbon lakes are located at high latitudes.
Fabricating Genetically Engineered High-Power Lithium-Ion Batteries Using Multiple Virus Genes
Authors: Lee Yun Jung , Yi Hyunjung , Kim Woo-Jae , Kang Kisuk , Yun Dong Soo , Strano Michael S. , Ceder Gerbrand , Belcher Angela M.
Published: April 2009

Viral Battery

In developing materials for batteries, there is a trade-off between charge capacity, conductivity, and chemical stability. Nanostructured materials improve the conductivity for some resistive materials, but fabricating stable materials at nanometer-length scales is difficult. Harnessing their knowledge of viruses as toolkits for materials fabrication,

Lee
et al.

(p. 1051; published online 2 April) modified two genes in the filamentous bacteriophage M13 to produce a virus with an affinity for nucleating amorphous iron phosphate along its length and for attaching carbon nanotubes at one of the ends. In nanostructured form, the amorphous iron phosphate produced a useful cathode material, while the carbon nanotubes formed a percolating network that significantly enhanced conductivity.
Human- and Plant-Pathogenic
Pseudomonas
Species Produce Bacteriocins Exhibiting Colicin M-Like Hydrolase Activity towards Peptidoglycan Precursors
Authors: Barreteau Hélène , Bouhss Ahmed , Fourgeaud Martine , Mainardi Jean-Luc , Touzé Thierry , Gérard Fabien , Blanot Didier , Arthur Michel , Mengin-Lecreulx Dominique
Published: April 2009

Genes encoding proteins that exhibit similarity to the C-terminal domain of
Escherichia coli
colicin M were identified in the genomes of some
Pseudomonas
species, namely,
P. aeruginosa, P. syringae
, and
P. fluorescens
. These genes were detected only in a restricted number of strains. In
P. aeruginosa
, for instance, the colicin M homologue gene was located within the ExoU-containing genomic island A, a large horizontally acquired genetic element and virulence determinant. Here we report the cloning of these genes from the three
Pseudomonas
species and the purification and biochemical characterization of the different colicin M homologues. All of them were shown to exhibit Mg
2+
-dependent diphosphoric diester hydrolase activity toward the two undecaprenyl phosphate-linked peptidoglycan precursors (lipids I and II) in vitro. In all cases, the site of cleavage was localized between the undecaprenyl and pyrophospho-MurNAc moieties of these precursors. These enzymes were not active on the cytoplasmic precursor UDP-MurNAc-pentapeptide or (or only very poorly) on undecaprenyl pyrophosphate. These colicin M homologues have a narrow range of antibacterial activity. The
P. aeruginosa
protein at low concentrations was shown to inhibit growth of sensitive
P. aeruginosa
strains. These proteins thus represent a new class of bacteriocins (pyocins), the first ones reported thus far in the genus
Pseudomonas
that target peptidoglycan metabolism.
If you build it, will they come? Using a mobile safety centre to disseminate safety information and products to low-income urban families
Authors: Gielen A C , McDonald E , Frattaroli S , McKenzie L B , Backes B , Glenshaw M , Shields W , Bulzacchelli M T ,   for the CareS (Children are Safe) Mobile Safety Center Partnership
Published: April 2009

Objective:

To examine the utilisation-related outcomes associated with visiting the Johns Hopkins CareS (ChildrenareSafe) Mobile Safety Center (MSC), a 40-foot vehicle designed to deliver effective injury prevention interventions and education to low-income urban families.

Design and setting:

Utilisation-related data were collected when the MSC was accessible at a community health centre and at community events from August 2004 to July 2006 in Baltimore City.

Subjects:

Adults bringing their child for well child care at a community health centre and MSC visitors at community events.

Interventions:

Low-cost safety products and free personalised educational services are provided on the MSC, which replicates a home environment and contains interactive exhibits.

Main outcome measures:

Perceived benefits of visiting the MSC; products and services received.

Results:

MSC visitors (n = 83) and non-visitors (n = 127) did not differ in sociodemographic and injury-related characteristics; 96% of visitors reported learning something new as a result of their visit and 98% would recommend the MSC. During the first 2 years of operation, the MSC made 273 appearances, serving 6086 people. Home child safety products accounted for 71% of the 559 products distributed; educational materials made up 87% of the 7982 services received. Car safety seats accounted for 23% of the products distributed; installations made up 4% of the services received.

Conclusions:

This approach to disseminating injury prevention interventions holds promise for enhancing the appeal of safety information and increasing the protection of children.
Working conditions of bus drivers in the private sector and bus crashes in Kandy district, Sri Lanka: a case–control study
Authors: Jayatilleke A U , Nakahara S , Dharmaratne S D , Jayatilleke A C , Poudel K C , Jimba M
Published: April 2009

Objective:

To explore the effects of working conditions of private-bus drivers on bus crashes in Kandy district, Sri Lanka.

Methods:

A case–control study was carried out from August to September 2006. All private-bus drivers registered in Kandy district and involved in crashes reported to the police between November 2005 and April 2006 (n = 63) were selected as cases. Two control groups were included: private-bus drivers working on the same routes as the case drivers (n = 90) and private-bus drivers selected randomly from other routes of the district (n = 111). Data were collected using an anonymous self-administered questionnaire. Associations between working conditions and crashes were analysed using logistic regression.

Results:

A strong association was observed between drivers’ disagreements about working hours and bus crashes (matched controls, adjusted odds ratio (AOR) 5.98, 95% CI 1.02 to 34.90; unmatched controls, AOR 18.74, 95% CI 2.00 to 175.84). A significant association was also observed between low salaries (<US$100) and private-bus crashes (matched controls, AOR 1.01, 95% CI 0.40 to 2.54; unmatched controls, AOR 3.09, 95% CI 1.26 to 7.57).

Conclusions:

Drivers’ disagreements about working hours and low salaries were significant risk factors for private-bus crashes in Kandy district, Sri Lanka. Therefore, new legislation for private-bus owners on the working hours and salaries of their drivers to prevent private-bus crashes is recommended.
Methodological approaches used to assess the relationship between parental supervision and child injury risk
Authors: Petrass L A , Finch C F , Blitvich J D
Published: April 2009

Objective:

To describe and rate the quality of methodological approaches used to measure parental supervision in relation to injury risk in children aged 0–14 years.

Design:

A systematic review of the literature related to supervision and injury risk.

Methods:

A comprehensive search of electronic databases from the earliest records available to the end of 2007, and supplemental hand-searching of relevant journals, reference lists of studies identified through database searches, and bibliographies of systematic and non-systematic reviews. A classification scale was used to rate the methodological quality of studies.

Results:

30 papers met the inclusion criteria. They varied substantially in quality, and no meta-analyses or randomised controlled trials were identified. Fifteen studies used self-report approaches, asking parents or care givers to report through recording diaries, interviews and questionnaires and were considered of low quality; 11 studies reconstructed injury outcomes retrospectively. Observational studies were conducted in both laboratory and natural settings (n = 6), and these studies were generally of higher quality than self-report methods.

Conclusions:

The quality of many supervision and child injury risk studies is low to moderate. Further development of methodological approaches is needed to improve studies of the relationship between supervision and child injury risk.
Analysis of the childhood fatal drowning situation in Bangladesh: exploring prevention measures for low-income countries
Authors: Rahman A , Mashreky S R , Chowdhury S M , Giashuddin M S , Uhaa I J , Shafinaz S , Hossain M , Linnan M , Rahman F
Published: April 2009

Objective:

To determine the epidemiology of child drowning in order to propose possible interventions for Bangladesh and other similar low-income countries.

Design:

Population-based cross-sectional study.

Setting:

Rural and urban communities in Bangladesh.

Subjects:

About 352 000 children 0–17 years were selected from over 171 000 households, using multistage cluster sampling.

Main outcome measures:

Incidence of fatal drowning.

Results:

Drowning was the leading cause of death (28.6 per 100 000 child-years) in children aged 1–17 years. The highest incidence (86.3 per 100 000 child-years) was in children aged 1–4 years. More than two-thirds of drownings occurred in ponds and ditches. Most drownings (85%) happened in daylight. In more than one-third of cases of drowning, the child was alone. In the two-thirds of cases in which the child was accompanied, almost half were with children who were 10 years or below. Only 7% of drowned children over 4 years of age knew how to swim.

Conclusions:

Drowning is a major cause of childhood mortality in Bangladesh. Creating drowning-safe homes, improving supervision of children, modifying the environment, and developing water safety skills for children and the community may be effective interventions for drowning prevention.
Structural analysis of the Velardeña mining district, Mexico: a faulted Au–Ag-rich hydrothermal system
Authors: Pinet Nicolas , Tremblay Alain
Published: April 2009

Epithermal Au–Ag veins of the Velardeña mining district (north-central Mexico) correspond to narrow, fault-controlled, high-grade structures that are continuous along strike for several kilometres. The veins converge toward the Guardarraya intrusion where carbonate-hosted deposits are found at the contact with surrounding limestones. The mineralized structures are cut by Basin and Range normal faults showing apparent vertical displacement up to 320 m. Paleostress reconstructions in the Velardeña mining district suggest that mineralized structures formed during a NNE-directed extensional event that predated the Basin and Range faulting event (ENE-directed). Basin and Range normal faulting is responsible for surface exposures of various Au–Ag mineralizations formed at different crustal depths, thus enabling studies of the entire hydrothermal system—from low-grade breccia zones in the volcanic cover rocks to deeper base-metal-rich deposits.
The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?
Authors: Shi Zheng , Hsieh Yih-huang , Weinberg Noham , Wolfe Saul
Published: April 2009

A computational strategy that reproduces the experimental rates of hydration of formaldehyde, acetaldehyde, acetone, and cyclohexanone and the rates of acetic acid and 2-hydroxypyridine-catalyzed hydration of acetone has been extended to the results of the neutral hydrolysis of methyl acetate reported in Part 1. Calculations have been performed for one-step and two-step mechanisms, with cooperative assistance from one to three additional water molecules in the presence and absence of the acetic acid product. The calculations predict that, for the neutral reaction, a one-step mechanism will be favoured if tetrahedral intermediates have a short lifetime and do not interconvert prior to breakdown (case A), and a two-step mechanism will be operative if tetrahedral intermediates are allowed to interconvert prior to breakdown (case B). The experimental results are consistent with the predictions of case A. In the presence of acetic acid, case A predicts that the acid will contribute only 1.6% to the overall rate, a negligible acceleration over the noncatalytic process, and case B predicts general acid catalysis to be an order of magnitude greater than the experimental result. It is concluded that the neutral hydrolysis of methyl acetate is mainly a cooperative one-step process, and that general acid catalysis by the acetic acid product does not occur.
Measurement and calculation of 13C and 15N NMR chemical-shift tensors of a push–pull ethylene
Authors: Amini Saeed K. , Tafazzoli Mohsen , Jenkins Hilary A. , Goward Gillian R. , Bain Alex D.
Published: April 2009

Methyl 3-dimethylamino-2-cyanocrotonate (MDACC) has a remarkably weak carbon–carbon double bond. It has strong electron-withdrawing groups on one end and electron-donating groups on the other: a so-called push–pull ethylene. To investigate this unusual electronic structure, we have determined the crystal structure and measured both the 13C and 15N NMR chemical-shift tensors. These measurements are supplemented by shielding-tensor calculations done with density functional methods. The large difference (approximately 100 ppm) between isotropic chemical shifts of the two alkenyl carbons reflects a large charge release from the electron-donating side of C=C double bond to the electron-withdrawing groups. Comparison of the calculated orientations of the principal components of the alkenyl carbons obtained from ab initio calculations shows that the primary changes in charge density occur in the molecular plane. On the other hand, smaller charge density changes above and below the plane of the C=C double bond establish the conjugation of donor and acceptor groups with π* and π molecular orbitals of the central double bond, respectively, which lowers the barrier to rotation about this bond.
Mapping the sirodesmin PL biosynthetic pathway — A remarkable intrinsic steric deuterium isotope effect on a 1H NMR chemical shift determines β-proton exchange in tyrosine
Authors: Pedras M. Soledade C. , Yu Yang
Published: April 2009

Sirodesmin PL is both an antibiotic and a phytotoxin produced by a fungal plant pathogen ( Leptosphaeria maculans, asexual stage Phoma lingam ) that causes blackleg disease on crucifers. To determine potential biosynthetic precursors of sirodesmin PL, deuterated compounds were synthesized and incubated with cultures of L. maculans. Incorporations of deuterium into sirodesmin PL (7) and its precursor phomamide (4) were determined using 1H and 13C NMR spectroscopy, LC-HRMS-ESI and HRMS-EI spectrometry. Spectroscopic analyses established that [3,3-2H2]l-tyrosine (1a), [3,3-2H2]O-prenyl-l-tyrosine (9a), [3,3,5′,5′,5′-2H5]O-prenyl-l-tyrosine (9b), and [5,5-2H2]phomamide (4a) were incorporated efficiently into sirodesmin PL (7). Interestingly, an unexpected “twist” revealed that one of the β-deuteria (pro-R) of [3,3-2H2]l-tyrosine (1a) was exchanged stereospecifically before incorporation into sirodesmin PL (7). As well, our studies revealed that O-prenyl-l-tyrosine is likely to be the first committed precursor en route to sirodesmin PL (7).
THE CONTINUOUS STOP LOCATION PROBLEM IN PUBLIC TRANSPORTATION NETWORKS
Authors: SCHöBEL ANITA , HAMACHER HORST W. , LIEBERS ANNEGRET , WAGNER DOROTHEA
Published: April 2009

In this paper we consider the location of stops along the edges of an already existing public transportation network. This can be the introduction of bus stops along some given bus routes, or of railway stations along the tracks in a railway network.

The positive effect of new stops is given by the better access of the potential customers to public transportation, while the travel time increases due to the additional stopping activities of the trains. The latter leads to a negative effect for the customers. The goal is to cover all given demand points with a minimal amount of additional traveling time, where covering may be defined with respect to an arbitrary norm or gauge. This problem is NP-hard, even in the special case of Euclidean distances. In this paper, we derive a finite candidate set leading to a discrete set covering problem. Moreover, we identify network structures in which the coefficient matrix of the resulting set covering problem is totally unimodular, such that the problem can be solved efficiently in this case. Extensions of the problem are also discussed.