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Results for “assembly operations”

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At least 73 records · Page 4Linked to original sources
PubMed1994

Construction of a 28-mm 1H/13C probe and actively shielded Z-gradient set for operation in a 9.4 T/89 mm magnet.

In this work, we present a new RF and gradient assembly for operation in a 9.4 Tesla/89 mm magnet. This assembly was designed in order to enable 1H-NMR perfusion studies that are based on proton-observed carbon-edited approaches or gradient selected double quantum coherence. The RF portion of this probe assembly is comprised of a modified Alderman-Grant coil and a saddle coil operating at 400 and 100 MHz, respectively. These coils are surrounded by an actively shielded Z gradient, which also allows for the use of gradient-based water suppression without the need for carbon selection. We demonstrate that this probe can be used to implement gradient selected double quantum coherence experiments resulting in a high degree of water suppression.

Carbon Isotopes↗
PubMed2006

Conformations of three heterocyclic perhydropyrrolobenzofurans and polymeric assembly via co-operative intermolecular C-H...O hydrogen bonds.

In 1-cyclohexyl-6,6,8a-trimethyl-3a,6,7,8a-tetrahydro-1H-1-benzofuro[2,3-b]pyrrole-2,4(3H,5H)-dione, C19H27NO3, (I), and the isomorphous compounds 6,6,8a-trimethyl-1-phenyl-3a,6,7,8a-tetrahydro-1H-1-benzofuro[2,3-b]pyrrole-2,4(3H,5H)-dione, C19H21NO3, (II), and 6,6,8a-trimethyl-1-(3-pyridyl)-3a,6,7,8a-tetrahydro-1H-1-benzofuro[2,3-b]pyrrole-2,4(3H,5H)-dione, C18H20N2O3, (III), the tetrahydrobenzo-dihydrofuro-pyrrolidine ring systems are folded at the cis junction of the five-membered rings, giving rise to a non-planar shape of the tricyclic cores. The dihydrofuran and pyrrolidine rings in (I) are puckered and adopt an envelope conformation. The cyclohexene rings adopt a half-chair conformation in all the molecules, while the substituent N-cyclohexyl ring in (I) assumes a chair form. Short intramolecular C-H...O contacts form S(5) and S(6) motifs. The isomorphous compounds (II) and (III) are effectively isostructural, and aggregate into chains via intermolecular C-H...O hydrogen bonds.

Benzofurans↗
PubMed1995

Workplace Design for Manual Assembly Tasks: Effect of Spatial Arrangement on Work-Cycle Time.

This article reports the results of an experimental study undertaken to investigate the effect of spatial arrangement of assembly board and parts bin in the normal work area on work-cycle time in manual assembly tasks. Operator performance was measured in terms of average work-cycle time taken to complete a laboratory-simulated manual assembly task. Results showed that both location and distance factors had significant effects on work-cycle time. Effect of the size of parts was also investigated in the study. Average observed work-cycle times were compared with the methods-time measurement (MTM) values. Repetitive manual assembly tasks are common in industry and are thought to lead to musculoskeletal disorders. The results of this research are important for ergonomic design of the workplace for assembly tasks, which would help to enhance operators' efficiency.

assembly tasks↗
PubMed1988

Roles of operator and non-operator RNA sequences in bacteriophage R17 capsid assembly.

In order to understand the role of sequences other than the translational operator on bacteriophage R17 assembly, in vitro capsid assembly was studied with R17 coat protein and a variety of RNAs. For a series of RNA oligomers of the same chain length, sequences that bind coat protein dimer with a lower affinity require higher concentrations of RNA and protein for assembly. Among a series of non-specific RNA molecules of differing lengths, lower protein and RNA concentrations are required for assembly of capsids containing longer RNAs. For RNA molecules of any length, the presence of a single high-affinity translational operator sequence lowered the concentration requirements for capsid assembly. However, the advantage for encapsidation provided by the operator sequence is small for large RNA molecules. The experiments indicate that in the overall assembly process the interaction of coat protein with non-specific sequences is at least as important as its interaction with the specific translational operator sequence. In light of the data, a mechanism of achieving selective packaging of the R17 genomic RNA in vivo is discussed.

Bacteriophages↗
PubMed1975

A pneumatically operated femoral artery compressor.

A readily assembled, inexpensive pneumatically operated femoral artery compressor for use in transfemoral arteriography is described. This device is effective in controlling post-procedure bleeding and oozing around the catheter during the procedure.

Air↗
PubMed2004

In situ observations of water production and distribution in an operating H2/O2 PEM fuel cell assembly using 1H NMR microscopy.

Proton NMR imaging was used to investigate in situ the distribution of water in a polymer electrolyte membrane fuel cell operating on H2 and O2. In a single experiment, water was monitored in the gas flow channels, the membrane electrode assembly, and in the membrane surrounding the catalysts. Radial gradient diffusion removes water from the catalysts into the surrounding membrane. This research demonstrates the strength of 1H NMR microscopy as an aid for designing fuel cells to optimize water management.

Journal Article↗
PubMed2005

A new curriculum for hysteroscopy training as demonstrated by an objective structured assessment of technical skills (OSATS).

OBJECTIVE: The purpose of this study was to develop an effective curriculum to teach hysteroscopy, as well as to develop an objective assessment instrument (OSATS). STUDY DESIGN: All 24 residents in our training program attended a 3-hour hysteroscopy curriculum in each of 3 years. Each year after the curriculum, an OSATS was administered consisting of an assembly and operative task. Each task was evaluated with a task-specific checklist and a previously validated global assessment form. Twenty-four residents from an outside institution served as controls. All residents were examined by blinded and unblinded examiners. RESULTS: The reliability coefficient was .7857 for the checklist and .9763 for the global scale. Interrater reliability for the checklist was .7478 and ranged from .4222 to .9329 for the global instruments. Evaluation of construct validity revealed that the junior residents at both locations did significantly worse on the checklist and global scale than the senior residents for all 3 years of the study (P < .001). Those residents provided the curriculum did significantly better on both the checklist and the global scale than the resident controls with a mean of 45% versus 63% for the checklist and 18.3 versus 24.9 for the global score. (P = .001 checklist, P = .007 global scale). CONCLUSION: This curriculum is an effective way to impart knowledge and skill in the assembly and use of the operative hysteroscope. The checklist developed for this OSATS has excellent reliability and construct validity.

Clinical Competence↗
PubMed2005

The 274th Forward Surgical Team experience during Operation Enduring Freedom.

The 274th Forward Surgical Team (FST) was deployed in support of Operation Enduring Freedom from October 14, 2001 to May 8, 2002. During this period, the FST was asked to perform many nondoctrinal missions. The FST was tasked with functioning as a mini-combat support hospital during the earlier phases of Operation Enduring Freedom, performing in-flight surgical procedures and resuscitation of combat wounded, conducting split operations with surgical coverage of both Karshi and Khanabad, Uzbekistan, and Bagram, Afghanistan, and leading the multinational medical coalition assembled for Operation Anaconda and other combat operations staged from Bagram. Overall, the 274th FST took care of approximately 90% of U.S. combat casualties during this period and treated a total of 221 combat casualties. The FST treated 103 total surgical cases, including 73 with combat wounds. At the time, this experience with combat casualties and the surgical care of combat wounds was the largest since the Persian Gulf War. More importantly, this account describes the flow, frequency, and type of combat casualties seen in a low-intensity conflict like that being waged currently in Afghanistan. It is hoped that this depiction will aid in the preparation, equipping, and overall utilization of surgical assets in similar future conflicts.

Afghanistan↗
PubMed2004

Coordinating assembly and export of complex bacterial proteins.

The Escherichia coli twin-arginine protein transport (Tat) system is a molecular machine dedicated to the translocation of fully folded substrate proteins across the energy-transducing inner membrane. Complex cofactor-containing Tat substrates, such as the model (NiFe) hydrogenase-2 and trimethylamine N-oxide reductase (TorA) systems, acquire their redox cofactors prior to export from the cell and require to be correctly assembled before transport can proceed. It is likely, therefore, that cellular mechanisms exist to prevent premature export of immature substrates. Using a combination of genetic and biochemical approaches including gene knockouts, signal peptide swapping, complementation, and site-directed mutagenesis, we highlight here this crucial 'proofreading' or 'quality control' activity in operation during assembly of complex endogenous Tat substrates. Our experiments successfully uncouple the Tat transport and cofactor-insertion activities of the TorA-specific chaperone TorD and demonstrate unequivocally that TorD recognises the TorA twin-arginine signal peptide. It is proposed that some Tat signal peptides operate in tandem with cognate binding chaperones to orchestrate the assembly and transport of complex enzymes.

Bacteria↗
PubMed1992

Flagella in prokaryotes and lower eukaryotes.

During the past year, significant advances have been made in the understanding of both prokaryotic and eukaryotic flagella. About 50 genes are dedicated to the assembly and operation of bacterial flagella. Recent discoveries have advanced our understanding of how these genes are regulated and how their products assemble into a functional, rotating organelle. The dynein arms of eukaryotic flagella are now also better understood. Several genes that are found in the mechanochemical macroassemblies have been cloned, and other loci have been identified, suggesting that there is even greater complexity than first expected.

Animals↗
PubMed2000

Coupled energetics of lambda cro repressor self-assembly and site-specific DNA operator binding II: cooperative interactions of cro dimers.

The bacteriophage lambda relies on interactions of the cI and cro repressors which self assemble and bind the two operators (O(R) and O(L)) of the phage genome to control the lysogenic to lytic switch. While the self assembly and O(R) binding of cI have been investigated in detail, a more complete understanding of gene regulation by phage lambda also requires detailed knowledge of the role of cro repressor as it dimerizes and binds at O(R) sites. Since dimerization and operator binding are coupled processes, a full elucidation of the regulatory energetics in this system requires that the equilibrium constants for dimerization and cooperative binding be determined. The dimerization constant for cro has been measured as a prelude to these binding studies. Here, the energetics of cro binding to O(R) are evaluated using quantitative DNaseI footprint titration techniques. Binding data for wild-type and modified O(R) site combinations have been simultaneously analyzed in concert with the dimerization energetics to obtain both the intrinsic and cooperative DNA binding energies for cro with the three O(R) sites. Binding of cro dimers is strongest to O(R)3, then O(R)1 and lastly, O(R)2. Adjacently bound repressors exhibit positive cooperativity ranging from -0.6 to -1.0 kcal/mol. Implications of these, newly resolved, energetics are discussed in the framework of a dynamic model for gene regulation. This characterization of the DNA-binding properties of cro repressor establishes the foundation on which the system can be explored for other, more complex, regulatory elements such as cI-cro cooperativity.

Allosteric Site↗
PubMed1991

Phonological assembly in reading: lexical contribution leads to violation of graphophonological rules.

According to current models of reading, the phonological representation of a letter string could be generated by means of two different procedures. The first consists in the looking up or addressing of the phonological representation of the appropriate word in the mental lexicon. The second consists in the assignment of a phonological code to the various orthographic units that occur in the letter string and the assembly of them into a unitary phonological representation. However, the various models of phonological assembly differ in the nature of the knowledge that such assembly requires. On the one hand, dual-route theories assert that the assembly process operates by means of extralexical graphophonological rules and, therefore, without reference to lexical knowledge. On the other hand, in analogy theories and interactive models of phonological assembly, the lexical phonological representations of words orthographically close to the letter string (the orthographic neighborhood) are supposed to contribute to the translation process. The aim of the experiments reported here was to empirically distinguish between these two categories of models. In Experiment 1, subjects were asked to pronounce pseudowords containing the letter g. Results indicate that the phonological representation assigned to the letter g depends on the pronunciation favored by the lexical neighbors. Experiment 2 shows that lexical contribution to phonological assembly also takes place in lexical decision.

Adult↗
PubMed1997

Identification and status of design improvements to the NASA Shuttle EMU for International Space Station application.

To meet the significant increase in EVA demand to support assembly and operations of the International Space Station (ISS), NASA and industry have improved the current Shuttle Extravehicular Mobility Unit (EMU), or "space suit", configuration to meet the unique and specific requirements of an orbital-based system. The current Shuttle EMU was designed to be maintained and serviced on the ground between frequent Shuttle flights. ISS will require the EMUs to meet increased EVAs out of the Shuttle Orbiter and to remain on orbit for up to 180 days without need for regular return to Earth for scheduled maintenance or refurbishment. Ongoing Shuttle EMU improvements have increased reliability, operational life and performance while minimizing ground and on-orbit maintenance cost and expendable inventory. Modifications to both the anthropomorphic mobility elements of the Space Suit Assembly (SSA) as well as to the Primary Life Support System (PLSS) are identified and discussed. This paper also addresses the status of on-going Shuttle EMU improvements and summarizes the approach for increasing interoperability of the U.S. and Russian space suits to be utilized aboard the ISS.

Environment, Controlled↗
PubMedDate not supplied

A compact cryosurgical apparatus for minimally invasive procedures.

A new liquid-nitrogen-based apparatus for minimally invasive cryosurgery is presented. The cryoprobe was designed for application to breast tumors; however, it can be used for the treatment of other tumors. The cryoprobe has three major components, a cryoneedle, a thermal insulation shell, and a protective tube, which may be assembled as part of the operation. This special assembly keeps destruction to surrounding tissues due to cryoprobe penetration minimal, and allows accurate localization of the cryoprobe tip by means of stereotactic or needle-localization techniques. An alternative cryoprobe consists of a cryoneedle and a thermal insulation shell, which are rigidly connected. The liquid nitrogen supply system has two major components, an air-pressure source and a liquid nitrogen container, which are physically separated. This special configuration allows placement of the liquid nitrogen container adjacent to the cryotreated tissue and decreases the length of the cryoprobe feeding tube. In turn, heat losses to the surroundings are reduced, and therefore coolant consumption is reduced. The short feeding tube allows safe operation at low pressures. The small size of the apparatus makes it attractive for cryosurgical operations. It has been evaluated in gelatin solutions and in porcine skeletal muscle and liver. In-vivo results do not differ significantly from those obtained in gelatin solutions with regard to the dimensions of frozen regions. Using a three cryoprobe configuration, a frozen region with an average diameter of 50 mm and a length of 75 mm was obtained within 11 minutes. The thermal efficiency of that procedure was found to be 43%.

Air↗
PubMed2002

Chromatin assembly. Cooperation between histone chaperones and ATP-dependent nucleosome remodeling machines.

Chromatin is a highly dynamic structure that plays an essential role in regulating all nuclear processes that utilize the DNA template including DNA repair, replication, transcription and recombination. Thus, the mechanisms by which chromatin structures are assembled and modified are questions of broad interest. This minireview will focus on two groups of proteins: (a) histone chaperones and (b) ATP-dependent chromatin remodeling machines, that co-operate to assemble DNA and histone proteins into chromatin. The current understanding of how histone chaperones and ATP-dependent remodeling machines coordinately assemble chromatin in vitro will be discussed, together with the growing body of genetic evidence that supports the role of histone chaperones in the cell.

Adenosine Triphosphate↗
PubMed1989

Highly preferential nucleation of histone H1 assembly on scaffold-associated regions.

Scaffold-associated regions (SARs) are A + T-rich DNA regions of several hundred base-pairs that are known to bind specifically to nuclear or metaphase scaffolds. Surprisingly, histone H1 specifically associates with SARs. Under conditions of high co-operativity, at input ratios of H1 to DNA up to 15% (w/w), histone H1 binds preferentially to those DNA molecules harboring a SAR, leaving the non-SAR fragments free. Our experiments identify SARs as cis-acting sequences that nucleate co-operative H1 assembly along the SAR into the flanking non-SAR DNA. Experiments with simple DNA polymers implicate homopolymeric oligo(dA).oligo(dT) tracts in preferential histone H1 assembly. The homopolymer oligo(dA).oligo(dT) is, above a critical length of 130 base-pairs, a highly specific nucleator of H1 assembly. SARs may control the conformation of chromatin domains via a regulated H1 assembly and set up the potential transcriptional repertoire of the cell.

Animals↗