Assembly Of Arrays Research Articles

Synthesis and controlled assembly of α-FeOOH and α-Fe2O3 nanobelt arrays on hollow glass spheres

Novel systematically patterned 1D iron oxide nanostructure arrays assembled on hollow glass spheres (HGS) are successfully prepared, and thus low density core/shell composite hollow spheres are fabricated. Glass/α-FeOOH (akaganeite) composite spheres are synthesized firstly through a facile low-temperature hydrothermal process independent of surfactants or external forces. The α-FeOOH shells are assembled by nanobelts with a mean width of ca. 100nm and an average length of 700nm. After calcining at 400°C for 3.0h, α-Fe2O3 (hematite) nanostructure arrays grown on HGS can be obtained, preserving the same belt-like morphology. On the basis of a series of contrast experiments, the probable growth process of the akaganeite nanobelts on HGS is proposed. Magnetic measurements of the glass/α-Fe2O3 core/shell products are carried out, and the results show that the as-obtained products exhibit weakly ferromagnetic behaviors at room temperature, which are much enhanced at a lower temperature (5K).

CHD1 Contributes to Intestinal Resistance against Infection by P. aeruginosa in Drosophila melanogaster

Drosophila SNF2-type ATPase CHD1 catalyzes the assembly and remodeling of nucleosomal arrays in vitro and is involved in H3.3 incorporation in viin vivo during early embryo development. Evidence for a role as transcriptional regulator comes from its colocalization with elongating RNA polymerase II as well as from studies of fly Hsp70 transcription. Here we used microarray analysis to identify target genes of CHD1. We found a fraction of genes that were misregulated in Chd1 mutants to be functionally linked to Drosophila immune and stress response. Infection experiments using different microbial species revealed defects in host defense in Chd1-deficient adults upon oral infection with P. aeruginosa but not upon septic injury, suggesting a so far unrecognized role for CHD1 in intestinal immunity. Further molecular analysis showed that gut-specific transcription of antimicrobial peptide genes was overactivated in the absence of infection in Chd1 mutant flies. Moreover, microbial colonization of the intestine was elevated in Chd1 mutants and oral infection resulted in strong enrichment of bacteria in the body cavity indicating increased microbial passage across intestinal epithelia. However, we did not detect enhanced epithelial damage or alterations of the intestinal stem cell population. Collectively, our data provide evidence that intestinal resistance against infection by P. aeruginosa in Drosophila is linked to maintaining proper balance of gut-microbe interactions and that the chromatin remodeler CHD1 is involved in regulating this aspect.

Numerical Study of Thermal Performance of FC-PBGA Assembly with Extruded-fin Heatsink

The trend in microelectronics is toward increasingly higher input/output, higher component density and higher electrical performance, which makes thermal enhancement of package performance an increasingly important issue. In both natural and forced convection environments, three-dimensional finite element simulation is used to study thermal performance of a flip-chip plastic ball grid array (FCPBGA) assembly with an extruded-fin heatsink on top of the assembly. The finite element model is complete enough to include key elements such as bumps, solder balls, substrate, printed circuit board, vias and ground planes for both signal and power. Temperature fields are simulated and presented for several FC-PBGA assembly configurations. Thermal resistance is calculated to characterize and compare the thermal performance by considering alternative design parameters of the extruded-fin heatsink and the lid.

Two CheW coupling proteins are essential in a chemosensory pathway of Borrelia burgdorferi

In the model organism Escherichia coli, the coupling protein CheW, which bridges the chemoreceptors and histidine kinase CheA, is essential for chemotaxis. Unlike the situation in E. coli, Borrelia burgdorferi, the causative agent of Lyme disease, has three cheW homologues (cheW(1) , cheW(2) and cheW(3) ). Here, a comprehensive approach is utilized to investigate the roles of the three cheWs in chemotaxis of B. burgdorferi. First, genetic studies indicated that both the cheW(1) and cheW(3) genes are essential for chemotaxis, as the mutants had altered swimming behaviours and were non-chemotactic. Second, immunofluorescence and cryo-electron tomography studies suggested that both CheW(1) and CheW(3) are involved in the assembly of chemoreceptor arrays at the cell poles. In contrast to cheW(1) and cheW(3) , cheW(2) is dispensable for chemotaxis and assembly of the chemoreceptor arrays. Finally, immunoprecipitation studies demonstrated that the three CheWs interact with different CheAs: CheW(1) and CheW(3) interact with CheA(2) whereas CheW(2) binds to CheA(1) . Collectively, our results indicate that CheW(1) and CheW(3) are incorporated into one chemosensory pathway that is essential for B. burgdorferi chemotaxis. Although many bacteria have more than one homologue of CheW, to our knowledge, this report provides the first experimental evidence that two CheW proteins coexist in one chemosensory pathway and that both are essential for chemotaxis.

Multiscale modeling of residual stresses in isotropic conductive adhesives with nano-particles

Isotropic conductive adhesives (ICAs) are promising candidates for low temperature joining technologies in microelectronics, enabling ultra-fine pitch sizes. Especially in solar and automotive applications, long-term reliability is a prerequisite in new generation electronics. It is essential that reliability predictions take processing history into account in order to correctly address premature failures as well as to make sound long-term predictions. In this paper, residual stresses that develop in a nano-Ag ICA interconnect during the assembly of a flip-chip pin grid array are investigated. A multiscale modeling framework is adopted to link the nano-sized particles to the interconnect level. This is achieved by the numerical analysis of the mechanical response during the curing process through the computational homogenization approach, in which two boundary value problems, one at each scale are formulated and solved simultaneously, in a fully nested manner. The mechanical response of the interconnect is analyzed with respect to the particle volume fraction and distribution properties. It is shown that, although the overall residual stresses at the interconnect scale decrease with increasing the amount of conductive particles, at the particle scale local stress concentrations increase, indicating the possibility of damage and decohesion that might compromise mechanical integrity and interrupt the conductive path. Hence, the multiscale scheme proved crucial for the sound analysis of the nano-particle ICA interconnect problem, where consideration of only the interconnect level would lead to misleading conclusions.

Directed assembly of one-dimensional magic cluster arrays by domain boundaries

Directed assembly of one-dimensional magic cluster arrays by domain boundaries

Comparison approach on strain behavior of PBGA assembly by considering different thermal‐mechanical compound loading modes

PurposeThe purpose of this paper is to provide a systematic method to perform analysis and test for vibration‐thermal strain behavior of plastic ball grid array (PBGA) assembly by considering thermal and vibration loading mode. Also to investigate the dynamic behavior of PBGA assembly by considering loading modes for design and reliability evaluation of PBGA packaging.Design/methodology/approachA PBGA assembly prototype with different structure and material parameters is designed and manufactured. Based on investigation of the structural and physical parameters of PBGA sample, the vibration‐thermal strain test is developed to measure the strain distribution at the surface of the BT (bismaleimide triazine) substrates and PCB (printed circuit board) surface under vibration‐thermal cycling loading such as random vibration and the temperature is changed from 0°C to 100°C.FindingsThe test results show that the loading modes have different impact on PCB, EMC and substrate, respectively. In the meantime, it is shown that the characteristics of the compound mode is not the linear accumulative result by single vibration mode and single thermal loading mode as forecasted. The nonlinear mechanism for these modes application is the future work for progress.Research limitations/implicationsIt is very difficult to set up a numerical approach to illustrate the validity of the testing approach because the complex loading modes and the complex structure of PBGA assembly. The research on an accurate mathematical model of the PBGA assembly prototype is a future work.Practical implicationsIt implies a potential design characteristic for future application of PBGA assembly. It also builds a basis for future work for design and reliability evaluation of BGA package.Originality/valueThis paper fulfils useful information about the thermal‐vibration coupling dynamic behavior of PBGA assembly with different structure characteristics, materials parameters.

Molecular architecture of chemoreceptor arrays revealed by cryoelectron tomography of Escherichia coli minicells

The chemoreceptors of Escherichia coli localize to the cell poles and form a highly ordered array in concert with the CheA kinase and the CheW coupling factor. However, a high-resolution structure of the array has been lacking, and the molecular basis of array assembly has thus remained elusive. Here, we use cryoelectron tomography of flagellated E. coli minicells to derive a 3D map of the intact array. Docking of high-resolution structures into the 3D map provides a model of the core signaling complex, in which a CheA/CheW dimer bridges two adjacent receptor trimers via multiple hydrophobic interactions. A further, hitherto unknown, hydrophobic interaction between CheW and the homologous P5 domain of CheA in an adjacent core complex connects the complexes into an extended array. This architecture provides a structural basis for array formation and could explain the high sensitivity and cooperativity of chemotaxis signaling in E. coli.

Cep57, a NEDD1-binding pericentriolar material component, is essential for spindle pole integrity

Formation of a bipolar spindle is indispensable for faithful chromosome segregation and cell division. Spindle integrity is largely dependent on the centrosome and the microtubule network. Centrosome protein Cep57 can bundle microtubules in mammalian cells. Its related protein (Cep57R) in Xenopus was characterized as a stabilization factor for microtubule-kinetochore attachment. Here we show that Cep57 is a pericentriolar material (PCM) component. Its interaction with NEDD1 is necessary for the centrosome localization of Cep57. Depletion of Cep57 leads to unaligned chromosomes and a multipolar spindle, which is induced by PCM fragmentation. In the absence of Cep57, centrosome microtubule array assembly activity is weakened, and the spindle length and microtubule density decrease. As a spindle microtubule-binding protein, Cep57 is also responsible for the proper organization of the spindle microtubule and localization of spindle pole focusing proteins. Collectively, these results suggest that Cep57, as a NEDD1-binding centrosome component, could function as a spindle pole- and microtubule-stabilizing factor for establishing robust spindle architecture.

Computational fluid dynamic and thermal analysis for BGA assembly during forced convection reflow soldering process

Purpose – The purpose of this paper is to develop a thermal coupling method of a ball grid array (BGA) assembly during a forced convection reflow soldering process.

Characterization of the Arabidopsis Augmin Complex Uncovers Its Critical Function in the Assembly of the Acentrosomal Spindle and Phragmoplast Microtubule Arrays

Plant cells assemble the bipolar spindle and phragmoplast microtubule (MT) arrays in the absence of the centrosome structure. Our recent findings in Arabidopsis thaliana indicated that AUGMIN subunit3 (AUG3), a homolog of animal dim γ-tubulin 3, plays a critical role in γ-tubulin-dependent MT nucleation and amplification during mitosis. Here, we report the isolation of the entire plant augmin complex that contains eight subunits. Among them, AUG1 to AUG6 share low sequence similarity with their animal counterparts, but AUG7 and AUG8 share homology only with proteins of plant origin. Genetic analyses indicate that the AUG1, AUG2, AUG4, and AUG5 genes are essential, as stable mutations in these genes could only be transmitted to heterozygous plants. The sterile aug7-1 homozygous mutant in which AUG7 expression is significantly reduced exhibited pleiotropic phenotypes of seriously retarded vegetative and reproductive growth. The aug7-1 mutation caused delocalization of γ-tubulin in the mitotic spindle and phragmoplast. Consequently, spindles were abnormally elongated, and their poles failed to converge, as MTs were splayed to discrete positions rendering deformed arrays. In addition, the mutant phragmoplasts often had disorganized MT bundles with uneven edges. We conclude that assembly of MT arrays during plant mitosis depends on the augmin complex, which includes two plant-specific subunits.

Synthesis and Characterizations of Ternary InGaAs Nanowires by a Two-Step Growth Method for High-Performance Electronic Devices

InAs nanowires have been extensively studied for high-speed and high-frequency electronics due to the low effective electron mass and corresponding high carrier mobility. However, further applications still suffer from the significant leakage current in InAs nanowire devices arising from the small electronic band gap. Here, we demonstrate the successful synthesis of ternary InGaAs nanowires in order to tackle this leakage issue utilizing the larger band gap material but at the same time not sacrificing the high electron mobility. In this work, we adapt a two-step growth method on amorphous SiO(2)/Si substrates which significantly reduces the kinked morphology and surface coating along the nanowires. The grown nanowires exhibit excellent crystallinity and uniform stoichiometric composition along the entire length of the nanowires. More importantly, the electrical properties of those nanowires are found to be remarkably impressive with I(ON)/I(OFF) ratio >10(5), field-effect mobility of ∼2700 cm(2)/(V·s), and ON current density of ∼0.9 mA/μm. These nanowires are then employed in the contact printing and achieve large-scale assembly of nanowire parallel arrays which further illustrate the potential for utilizing these high-performance nanowires on substrates for the fabrication of future integrated circuits.

ChemInform Abstract: Recent Applications of the Suzuki—Miyaura Cross—Coupling to Complex Polycyclic Ether Synthesis

AbstractReview: ca. 100 refs.

Effects of Corner/Edge Bonding and Underfill Properties on the Thermal Cycling Performance of Lead Free Ball Grid Array Assemblies

Underfilling will almost certainly improve the performance of an area array assembly in drop, vibration, etc. However, depending on the selection of materials, the thermal fatigue life may easily end up worse than without an underfill. This is even more true for lead free than for eutectic SnPb soldered assemblies. If reworkability is required, the bonding of the corners or a larger part of the component edges to the printed circuit board (PCB), without making contact with the solder joints, may offer a more attractive materials selection. A 30 mm flip chip ball grid array (FCBGA) component with SAC305 solder balls was attached to a PCB and tested in thermal cycling with underfills and corner/edge bonding reinforcements. Two corner bond materials and six reworkable and nonreworkable underfills with a variety of mechanical properties were considered. All of the present underfills reduced the thermal cycling performance, while edge bonding improved it by up to 50%. One set of the FCBGAs was assembled with a SnPb paste and underfilled with a soft reworkable underfill. Surprisingly, this improved the thermal cycling performance slightly beyond that of the nonunderfilled assemblies, providing up to three times better life than for those assembled with a SAC305 paste.

A Small Package With 46-dB Isolation Between Tx and Rx Antennas Suitable for 60-GHz WPAN Module

A small package suitable for the mobile terminals of the 60-GHz wireless personal area network is proposed. Two antennas for Tx and Rx are integrated in the package. The antenna provides the end-fire radiation from the side face of the substrate. The package is mounted on the edge of a printed circuit board by using the ball grid array assembly. The antenna is composed of a post-wall waveguide and a slab waveguide with metal sidewalls. The gain and beamwidth are determined by the size of the slab waveguide. The sidewalls are for the design of the beamwidth in the -plane and for realizing the high isolation between Tx and Rx antennas. The beamwidths of the fabricated antenna were measured to be 47° and 46° in the - and -plane at 60 GHz, respectively. The gain more than 7.8 dBi was measured in the frequency range from 59 to 66 GHz. The package was fabricated for the evaluation of the isolation. The measured average isolation level between Tx and Rx antenna was 46.0 dB in the frequency range above. The antenna characteristics and isolation level are sufficient for the 60-GHz WPAN system.

DNA-Linker-Induced Surface Assembly of Ultra Dense Parallel Single Walled Carbon Nanotube Arrays

Ultrathin film preparations of single-walled carbon nanotube (SWNT) allow economical utilization of nanotube properties in electronics applications. Recent advances have enabled production of micrometer scale SWNT transistors and sensors but scaling these devices down to the nanoscale, and improving the coupling of SWNTs to other nanoscale components, may require techniques that can generate a greater degree of nanoscale geometric order than has thus far been achieved. Here, we introduce linker-induced surface assembly, a new technique that uses small structured DNA linkers to assemble solution dispersed nanotubes into parallel arrays on charged surfaces. Parts of our linkers act as spacers to precisely control the internanotube separation distance down to <3 nm and can serve as scaffolds to position components such as proteins between adjacent parallel nanotubes. The resulting arrays can then be stamped onto other substrates. Our results demonstrate a new paradigm for the self-assembly of anisotropic colloidal nanomaterials into ordered structures and provide a potentially simple, low cost, and scalable route for preparation of exquisitely structured parallel SWNT films with applications in high-performance nanoscale switches, sensors, and meta-materials.

Small-molecule inhibitors of NMO-IgG binding to aquaporin-4 reduce astrocyte cytotoxicity in neuromyelitis optica.

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of spinal cord and optic nerve caused by pathogenic autoantibodies (NMO-IgG) against astrocyte aquaporin-4 (AQP4). We developed a high-throughput screen to identify blockers of NMO-IgG binding to human AQP4 using a human recombinant monoclonal NMO-IgG and transfected Fisher rat thyroid cells stably expressing human M23-AQP4. Screening of ∼60,000 compounds yielded the antiviral arbidol, the flavonoid tamarixetin, and several plant-derived berbamine alkaloids, each of which blocked NMO-IgG binding to AQP4 without affecting AQP4 expression, array assembly, or water permeability. The compounds inhibited NMO-IgG binding to AQP4 in NMO patient sera and blocked NMO-IgG-dependent complement- and cell-mediated cytotoxicity with IC(50) down to ∼5 μM. Docking computations identified putative sites of blocker binding at the extracellular surface of AQP4. The blockers did not affect complement-dependent cytotoxicity caused by anti-GD3 antibody binding to ganglioside GD3. The blockers reduced by >80% the severity of NMO lesions in an ex vivo spinal cord slice culture model of NMO and in mice in vivo. Our results provide proof of concept for a small-molecule blocker strategy to reduce NMO pathology. Small-molecule blockers may also be useful for other autoimmune diseases caused by binding of pathogenic autoantibodies to defined targets.

STUDY ON LEAD-FREE SOLDER JOINT RELIABILITY BASED ON GRAIN ORIENTATION

During service, coefficient of thermal expansion (CTE) mismatch between different materials in electronic devices can lead to stress and strain concentration, and the creep and fatigue damage will accumulate, leading to final failure of solder joints. The main constituent of Pb-free solder joint is β-Sn, which is body-centered tetragonal metal. There is big difference in CTE and elastic modulus along different directions of β-Sn, showing strong anisotropy. Therefore, solder joints with different orientations show quite different thermo-mechanical responses. In this study, ball grid array (BGA) assemblies were subjected to thermal cycling, and the orientation of the solder joints was characterized by EBSD to track the orientation evolution in different solder joints. Surface Evolver was adopted to simulate the three-dimensional shape of the solder joint. Based on the shape and grain structure of real lead-free solder joints, the thermal stress and strain distribution in BGA assemblies under thermal loading were computed. Sub-model based on grain numbers and orientation distribution is solved to get the strain distribution of the three typical solder joints. The experimental and simulated results show that grain orientation significantly influences the solder joint reliability and failure mode. For single-grained solder joints, stress and strain concentration is located in the solder bulk near the interface, where recrystallization accompanied with initiation and propagation of cracks. However, for

1,1’-Bis(diphenylphosphino)ferrocene in functional molecular materials

The bidentate ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf) is a widely used component in catalytic systems and its role in this capacity has been expertly reviewed elsewhere. The focus of this Perspective is the increasing use of dppf in the synthesis and matrix of 21st century materials. The ferrocene core imparts fine control to catalytic C-C and C-X coupling reactions used to manufacture a range of functional macromolecules from tailored dyes and OLED components to precisely engineered conducting polymers and thermoplastics. This ligand's limited flexibility resembles a ball and socket joint with simultaneous rotation and constrained perpendicular freedom. This uniquely restricted range of movement stabilizes a diverse array of ground and transition states for these important transition metal catalysed coupling reactions. It may also contribute desirable mechanical or electronic functionality as a bridging or chelating component in a coordination array, metallocycle or larger supramolecular assembly. The ferrocene offers steric bulk and crystallinity to these materials aiding chemical stability and ease of handing. It's oxidizability assists characterization and may be tailored to provide or complement photo- or electroactivity. Dppf containing materials have been designed with diverse functions from cooperative luminescence to host-guest complexation. It is likely that this ubiquitous lab companion will increasingly find its way into the fabric or processing of future functional molecular materials.

WIRED AND WIRELESS REMOTELY CONTROLLED ULTRASONIC TRANSDUCER AND IMAGING APPARATUS

A remotely manipulatable ultrasound transducer element or transducer array permits an operator of an ultrasound system to be remotely located from a patient and yet remotely control the location of the element or array on a patient's body such as on the skin surface or within a body cavity. The transducer element or transducer array associated with motors and control circuits comprises an assembly within a housing for fixation to or within a human body and is intended to be placed one time and then remotely manipulated in directions of rotation, twist, and linearly in first and second perpendicular directions within a plane parallel to the surface of the human body and remotely controlled to provide therapeutic or diagnostic treatment or imaging of an internal body region of interest under study. In one embodiment, the housing comprises at least one motor and one of a transducer element and a transducer array which is mounted to a rotor of the motor via an optional gear assembly for rotation, for example, in a range of 180 degrees so that multiple planes of imaging can be obtained, for example, of a heart or other body organ from the skin surface. The remotely manipulatable ultrasound transducer or transducer array assembly may comprise a wireless transceiver having a unique identifier for communication with one or more remote workstations, each having a unique identifier. Motors may provide linear, longitudinal axis movement, perpendicular movement to a longitudinal axis, rotation, twist and focus. Control information may comprise pulsing frequency, delay between elements, beamforming, time of day, direction, frequency, amplitude and the like to control one or more transducer elements or transducer arrays for therapeutic, diagnostic or imaging purposes.