Crossover Connection Research Articles

A novel broadband 3 × 4 Butler matrix beamforming network without crossovers

AbstractA novel broadband three‐input four‐output (3 × 4) Butler matrix (BM) without crossover is presented for the wider band operation. The proposed 3 × 4 BM is composed of three 3 dB branch‐line directional couplers, one T‐splitter power divider, and two 90° phase shifters. Unlike the traditional BM, the proposed BM network has successfully eliminated the crossover connection for simplifying the network, which operates in a wide operating range. For the validation of the design, a planar single‐layer 3 × 4 BM working at the frequency band of 1.69–2.69 GHz is designed, fabricated, and measured. The measurement result gives bandwidth up to 46% with return loss better than 14.3 dB at the full operating frequency band.

Lap Joint Resistivity and Crossover Resistance of REBCO Conductors and Coils

During the NHMFL 32 T magnet project, a program to develop a reliable method for making soldered lap joints between REBCO tape conductors was initiated. A standard process was adopted during the program, and then applied during coil fabrication and for quality control (QC) of incoming conductor. For each unique REBCO conductor piece procured for the 32 T project, a lap solder joint was made using the standard process and tested for resistance in liquid nitrogen. A total of 211 lap joints were made and tested. For the NHMFL 40 T magnet project, a similar study was performed using the same standard process on conductors procured for test coils. A total of 38 lap joints were made and tested. Results from both data sets are reported, and compared with findings from the initial study and published findings by others. In the stacked double-pancake construction adopted by the NHMFL for REBCO coils, each double-pancake is connected in series to adjacent modules with a crossover connection, made from an assembly of several REBCO tapes placed in parallel and soldered across the terminal ends of each adjacent module. Resistances of the crossovers in a 32 T test coil and from test articles and test coils made during the 40 T project, are reported here. The resistivity of the crossovers is estimated and compared with the findings from the lap joint measurements.

High performance planar micro-transformer using novel crossover connection

In this paper a novel planar micro-transformer with high performance is presented. Non-uniform current density distribution, especially in inner turn, increases the effective metal resistance due to skin and proximity effect. In order to overcome this problem, a novel crossover connection between turns has been used to make equal current paths in the turns and uniform the current distribution. By reducing the current crowding effects, the effective resistance is minimized, thereby the transformer performance characteristics can be increased. Simulation has been taken using ADS Momentum and HFSS software. The results show that the quality factor, self-inductance, mutual inductance and coupling factor are about 42.6, 4.9, 3.3 nH, 0.747 respectively, at 3.5 GHz frequency. The footprint of proposed structure is 860 μm × 860 μm. Compare with conventional micro-transformer, 17% in quality factor, 5% in coupling coefficient and more than 20% in self and mutual inductance improvement has been achieved.

EXPERIMENTAL INVESTIGATIONS OF INTERACTION OF TRACK AND ROLLING STOCK ON CROSSOVERS

Purpose. Recently on the Ukrainian railways network more attention is paid to the cases of violations in the maintenance of crossovers, which may lead to deterioration of the train traffic safety conditions. As a rule, such violations occur as a result of inaccuracies during crossover pegging and laying, as well as are the consequence of impact of rolling stock and thermal forces. The appearance of geometrical irregularities can also be triggered by violation of the scheme of layout of concrete sleepers in the crossover turnout curve with intertrack spaces of less than 5.3 m. Therefore, we have decided to analyze the impact of the presence of deviations from the layout scheme of the sleepers and geometric irregularities on the conditions of track and rolling stock interaction based on the results of experimental investigations. It was also decided to establish a connection between the stress-strain states of the track and the presence of short sleepers. Methodology. The effect of deviations from the layout scheme of the sleepers and geometric irregularities on the interaction conditions of track and rolling stock was studied by means of theoretical calculations and experimental research. The experimental research covered the area on the non-public railway tracks that meets the required conditions for scientific and research work on the territory of «Transinvestservice» company. Findings. The distribution of stresses and forces acting on a railway track depending on speed movement of experienced rolling stock was obtained. In addition we obtained the data on the influence of the sleeper geometric parameters on its stress-strain state. Originality. For the first time the paper assessed the impact of rolling stock in the presence of geometrical irregularities and asymmetrically truncated sleepers within the crossover connection part on the stress-strain state of track in this zone. In addition, we compared the results for the area with common and shortened sleepers. Practical value. The obtained experimental data allowed determining that the stress-strain state of the track structure in the crossover turnout curve at rolling stock speeds of up to 40 km/h fulfills the conditions of strength and stability. These results can be used to test mathematical models and theoretical studies on the development of standards for the maintenance of crossovers. The level of the obtained vertical, lateral forces and stresses practically does not depend on the presence of the truncated part of the sleepers, which are stacked in crossovers.

Role of the Barrier Dysfunction of the Intestines in the Development of Alimentary Allergy in Children

Intestinal epithelial barrier plays an important role in prevention of bacterial translocation and food allergens penetration. Article is dedicated to intestinal epithelial barrier disfunctions leading to sensitization. Special attention is paid to molecular mechanisms increasing the allergens penetration through intestinal wall. Phase of sensitization is characterized by antigen-induced crossover IgE connection with FcRI receptor on the surface of mast cell which leads to anaphylactic reaction. Key words : infants, food allergy, sensitization, intestinal epithelial barrier.

Where the Truth Lies (review)

Reviewed by: Where the Truth Lies Deborah Stevenson Warman, Jessica. Where the Truth Lies. Walker, 2010. [304p.] ISBN 978-0-8027-2078-8 $16.99 Reviewed from galleys R Gr. 8-12. Stonybrook Academy is all that Emily knows—her father has been headmaster at the posh boarding school in Connecticut as long as she can remember, and she loves dorm life in the quad with her friends. Her junior year marks a change, however, as she becomes smitten with bad boy Del, despite—or perhaps because of—her father's uncharacteristic warning about him. Her carelessness with Del leads to secret pregnancy and the birth of a baby who's immediately given up for adoption, and then Emily discovers that her beloved, seemingly staid parents have kept some deeply important secrets from her as well, secrets that reveal the truth about her lifelong night terrors and her own origins. Warman, author of the excellent Breathless (BCCB 11/09), returns here to the boarding-school milieu she continues to depict with finesse and tantalizing detail (though it's set at a different school, the book has some crossover connection to Breathless through one character); the hothouse intensity and ramped-up intimacy of life in Emily's dorm is yearningly credible. The book skillfully brings that same intensity to Emily's romance with Del, a relationship colored by disturbing undertones of control and projection. There's a soap-operatic generosity with dramatic plot elements and backstory here, especially in the multiple layers of family secrets that Emily must eventually penetrate, but Warman's fluid, sensitive writing flows past the contrivances; it's certainly plausible that Emily's own experiences end up informing her ultimate reaction to the revelations about her past. This is a smart, sensitive melodrama for readers who relished the hothouse world of Breathless. Copyright © 2010 The Board of Trustees of the University of Illinois

The Structure of the MAP2K MEK6 Reveals an Autoinhibitory Dimer

MAP2Ks are dual-specificity protein kinases functioning at the center of three-tiered MAP kinase modules. The structure of the kinase domain of the MAP2K MEK6 with phosphorylation site mimetic aspartic acid mutations (MEK6/DeltaN/DD) has been solved at 2.3 angstroms resolution. The structure reveals an autoinhibited elongated ellipsoidal dimer. The enzyme adopts an inactive conformation, based upon structural queues, despite the phosphomimetic mutations. Gel filtration and small-angle X-ray scattering analysis confirm that the crystallographically observed ellipsoidal dimer is a feature of MEK6/DeltaN/DD and full-length unphosphorylated wild-type MEK6 in solution. The interface includes the phosphate binding ribbon of each subunit, part of the activation loop, and a rare "arginine stack" between symmetry-related arginine residues in the N-terminal lobe. The autoinhibited structure likely confers specificity on active MAP2Ks. The dimer may also serve the function in unphosphorylated MEK6 of preventing activation loop phosphorylation by inappropriate kinases.

Optical implementation of rearrangeable nonblocking double banyan interconnection network in free space

The banyan network plays an important role in optical interconnection networks. A smart and compact double banyan network with cascading banyan network and inverse banyan network is proposed by using a polarizing beam-splitter (PBS), a phase spatial light modulator (PSLM), a half-wave plate (HWP), a double-faced reflective mirror (DFRM), and mirrors. The PBS features that the s-component (perpendicular to the incident plane) of the incident light beam is reflected, and the p-component (parallel to the incident plane) passes through it. Simultaneously, the bipartition graph algorithm (BGA) is adopted to ascertain the state of the node switch in each node stage (straight or crossover connection). According to switching logic, under control of external electrical signals, the PSLM functions to control routing paths of the signal beams, i.e. the polarization of each optical signal is rotated or not rotated 90° by a programmable PSLM. Since the proposed optical setup consists of only optical polarization elements, it is compact in structure, and possesses a low energy loss, a high signal-to-noise ratio and an available large number of optical channels. Finally, the discussions and the experimental results show that the double banyan network proposed here, owing to without signal blocking and conflict, may be used in optical communication and optical information processing.

The Crystal Structure of Progesterone 5β-Reductase from Digitalis lanata Defines a Novel Class of Short Chain Dehydrogenases/Reductases

Progesterone 5beta-reductase (5beta-POR) catalyzes the stereospecific reduction of progesterone to 5beta-pregnane-3,20-dione and is a key enzyme in the biosynthetic pathway of cardenolides in Digitalis (foxglove) plants. Sequence considerations suggested that 5beta-POR is a member of the short chain dehydrogenase/reductase (SDR) family of proteins but at the same time revealed that the sequence motifs that in standard SDRs contain the catalytically important residues are missing. Here we present crystal structures of 5beta-POR from Digitalis lanata in complex with NADP(+) at 2.3A and without cofactor bound at 2.4A resolution together with a model of a ternary complex consisting of 5beta-POR, NADP(+), and progesterone. Indeed, 5beta-POR displays the fold of an extended SDR. The architecture of the active site is, however, unprecedented because none of the standard catalytic residues are structurally conserved. A tyrosine (Tyr-179) and a lysine residue (Lys-147) are present in the active site, but they are displayed from novel positions and are part of novel sequence motifs. Mutating Tyr-179 to either alanine or phenylalanine completely abolishes the enzymatic activity. We propose that the distinct topology reflects the fact that 5beta-POR reduces a conjugated double bond in a steroid substrate via a 1-4 addition mechanism and that this requires a repositioning of the catalytically important residues. Our observation that the sequence motifs that line the active site are conserved in a number of bacterial and plant enzymes of yet unknown function leads us to the proposition that 5beta-POR defines a novel class of SDRs.

A module design of rearrangeable nonblocking double omega optical network using binary optics elements

Omega network plays an important role in all optical communication and optical interconnection networks. In this paper, a novel technology, which binary optics element (micro-blazed grating array) can realize perfect shuffle transform including inverse perfect shuffle and left perfect shuffle, is proposed. Moreover, by a cascade of inverse perfect shuffle and left perfect shuffle, a multistage rearrangeable nonblocking omega network can be constructed. Simultaneously, the bipartition graph algorithm (BGA) is adopted to ascertain the state of node switch in each node stage (straight or crossover connection). At last, a module of the rearrangeable nonblocking omega network which is integrated with polarizing beam-splitter, half-wave plate, micro-blazed grating array, is presented. It can accomplish the functions of 8-channel signal beams’ sorting and switching without routing conflict and blocking, and has advantages of being compact in structure, easy to integrate, efficient in performance etc. Finally, both the theoretical analysis and the experimental result show that this module proposed here may be helpful in free-space optical interconnection network and optical information processing.

Mechanism of the Kinetically-Controlled Folding Reaction of Subtilisin

Like many secreted proteases, subtilisin is kinetically stable in the mature form but unable to fold without assistance from its prodomain. The existence of high kinetic barriers to folding challenges many widely accepted ideas, namely, the thermodynamic determination of native structure and the sufficiency of thermodynamic stability to determine a pathway. The purpose of this article is to elucidate the physical nature of the kinetic barriers to subtilisin folding and to show how the prodomain overcomes these barriers. To address these questions, we have studied the bimolecular folding reaction of the subtilisin prodomain and a series of subtilisin mutants, which were designed to explore the steps in the folding reaction. Our analysis shows that inordinately slow folding of the mature form of subtilisin results from the accrued effects of two slow and sequential processes: (1) the formation of an unstable and topologically challenged intermediate and (2) the proline-limited isomerization of the intermediate to the native state. The low stability of nascent folding intermediates results in part from subtilisin's high dependence on metal binding for stability. Native subtilisin is thermodynamically unstable in the absence of bound metals. Because the two metal binding sites are formed late in folding, however, they contribute little to the stability of folding intermediates. The formation of productive folding intermediates is further hindered by the topological challenge of forming a left-handed crossover connection between beta-strands S2 and S3. This connection is critical to propagate the folding reaction. In the presence of the prodomain, folding proceeds through one major intermediate, which is stabilized by prodomain binding, independent of metal concentration and proline isomerization state. The prodomain also catalyzes the late proline isomerizations needed to form metal site B. Rate-limiting proline isomerization is common in protein folding, but its effect in slowing subtilisin folding is amplified because of the instability of the intermediate and an apparent need for simultaneous isomerization of multiple prolines in order to create metal site B. Thus, the kinetically controlled folding reaction of subtilisin, although unusual, is explained by the accrued effects of events found in other proteins.

Hydrogen−Deuterium Exchange in Free and Prodomain-Complexed Subtilisin

Residue-specific exchange rates of 223 amide protons in free and prodomain-complexed subtilisin were determined in order to understand how the prodomain binding affects the energetics of subtilisin folding. In free subtilisin, amide protons can be categorized according to exchange rate: 74 fast exchangers (rates > or = 1 h(-1)); 52 medium exchangers (rates between 1 h(-1) and 1 day(-1)); 31 slow exchangers (rates between 1 day(-1) and 0.001 day(-1)). The remaining 66 amide proteins did not exchange detectibly over 9 months (k(obs) < year(-1)) and were denoted as core protons. Core residues occur throughout the main structural elements of subtilisin. Prodomain binding results in high protection factors (100-1000) in the central beta-sheet, particularly in the vicinity of beta-strands S5, S6, and S7 and the connecting loops between them. These connecting loops provide the ligands to the cation at metal site B. Overall, prodomain binding seems to facilitate the organization of the entire central beta-sheet and alpha-helix C in the left-handed crossover connection between beta-strands two and three. It also appears to facilitate the isomerization of multiple prolines late in folding, allowing the formation of metal site B. The gain of stability region around site B comes at the cost of stability in regions more distal to prodomain binding: the C-terminal alpha-helix H and the N-terminal alpha-helices A and B. The acceleration of exchange in these regions by prodomain binding reveals an antagonism between the folding intermediate and the full native structure. This antagonism helps to explain why the prodomain is needed to stabilize the folding intermediate as well as why the unfolding of free subtilisin seldom occurs via this intermediate.

Docking Interactions Induce Exposure of Activation Loop in the MAP Kinase ERK2

MAP kinases bind activating kinases, phosphatases, and substrates through docking interactions. Here, we report a 1.9 A crystallographic analysis of inactive ERK2 bound to a "D motif" docking peptide (pepHePTP) derived from hematopoietic tyrosine phosphatase, a negative regulator of ERK2. In this complex, the complete D motif interaction defined by mutagenic analysis is observed, including extensive electrostatic interactions with the "CD" site of the kinase. Large conformational changes occur in the activation loop where the dual phosphorylation sites, which are buried in the inactive form of ERK2, become exposed to solvent in the complex. Similar conformational changes occur in a complex between ERK2 and a MEK2 (MAP/ERK kinase-2)-derived D motif peptide (pepMEK2). D motif peptides are known to bind homologous loci in the MAP kinases p38alpha and JNK1, also inducing conformational changes in these enzymes. However, the binding interactions and conformational changes are unique to each, thus contributing to specificity among MAP kinases.

Activation of the Hetero-octameric ATP Phosphoribosyl Transferase through Subunit Interface Rearrangement by a tRNA Synthetase Paralog

ATP phosphoribosyl transferase (ATP-PRT) joins ATP and 5-phosphoribosyl-1-pyrophosphate (PRPP) in a highly regulated reaction that initiates histidine biosynthesis. The unusual hetero-octameric version of ATP-PRT includes four HisG(S) catalytic subunits based on the periplasmic binding protein fold and four HisZ regulatory subunits that resemble histidyl-tRNA synthetases. Here, we present the first structure of a PRPP-bound ATP-PRT at 2.9 A and provide a structural model for allosteric activation based on comparisons with other inhibited and activated ATP-PRTs from both the hetero-octameric and hexameric families. The activated state of the octameric enzyme is characterized by an interstitial phosphate ion in the HisZ-HisG interface and new contacts between the HisZ motif 2 loop and the HisG(S) dimer interface. These contacts restructure the interface to recruit conserved residues to the active site, where they activate pyrophosphate to promote catalysis. Additionally, mutational analysis identifies the histidine binding sites within a region highly conserved between HisZ and the functional HisRS. Through the oligomerization and functional re-assignment of protein domains associated with aminoacylation and phosphate binding, the HisZ-HisG octameric ATP-PRT acquired the ability to initiate the synthesis of a key metabolic intermediate in an allosterically regulated fashion.

Theoretical and Experimental Design of Atypical Kinase Inhibitors: Application to p38 MAP Kinase

Mimics of the benzimidazolone nucleus found in inhibitors of p38 kinase are proposed, and their theoretical potential as bioisosteres is described. A set of calculated descriptors relevant to the anticipated binding interaction for the fragments 1-methyl-1H-benzotriazole 5, 3-methyl-benzo[d]isoxazole 3, and 3-methyl-[1,2,4]triazolo[4,3-a]pyridine 4, pyridine 1, and 1,3-dimethyl-1,3-dihydro-benzoimidazol-2-one 2 are reported. The design considerations and synthesis of p38 inhibitors based on these H-bond acceptor fragments is detailed. Comparative evaluation of the pyridine-, benzimidazolone-, benzotriazole-, and triazolopyridine-based inhibitors shows the triazoles 20 and 25 to be significantly more potent experimentally than the benzimidazolone after which they were modeled. An X-ray crystal structure of 25 bound to the active site shows that the triazole group serves as the H-bond acceptor but unexpectedly as a dual acceptor, inducing movement of the crossover connection of p38alpha. The computed descriptors for the hydrophobic and pi-pi interaction capacities were the most useful in ranking potency.

Ribonuclease P protein structure: evolutionary origins in the translational apparatus.

The crystal structure of Bacillus subtilis ribonuclease P protein is reported at 2.6 angstroms resolution. This protein binds to ribonuclease P RNA to form a ribonucleoprotein holoenzyme with optimal catalytic activity. Mutagenesis and biochemical data indicate that an unusual left-handed betaalphabeta crossover connection and a large central cleft in the protein form conserved RNA binding sites; a metal binding loop may comprise a third RNA binding site. The unusual topology is partly shared with ribosomal protein S5 and the ribosomal translocase elongation factor G, which suggests evolution from a common RNA binding ancestor in the primordial translational apparatus.

1.9 A crystal structure of interleukin 6: implications for a novel mode of receptor dimerization and signaling.

Interleukin 6 (IL-6) has many biological activities in vivo, and deregulation has been implicated in many disease processes. IL-6, a 185 amino acid polypeptide was refolded, purified and crystallized. The crystals diffracted to beyond 1.9 A and the structure was solved using single isomorphous replacement. The X-ray structure of IL-6 is composed of a four helix bundle linked by loops and an additional mini-helix. 157 out of 185 residues are well defined in the final structure, with 18 N-terminal and 8 A-B loop amino acids displaying no interpretable electron density. The three-dimensional structure has been used to construct a model of IL-6 interacting with the IL-6 receptor (alpha-chain) and gp130 (beta-chain) that gives new insight into the process of molecular recognition and signaling. Based on this model, we predict a fourth binding site on IL-6, a low affinity IL-6-IL-6 interaction, which may be necessary for the sequential assembly of a functional hexameric IL-6 receptor complex.

Three-dimensional Structure of Myelin Basic Protein: II. MOLECULAR MODELING AND CONSIDERATIONS OF PREDICTED STRUCTURES IN MULTIPLE SCLEROSIS

A computational model of myelin basic protein (MBP) has been constructed based on the premise of a phylogenetically conserved beta-sheet backbone and on electron microscopical three-dimensional reconstructions. Many residues subject to post-translational modification (phosphorylation, methylation, or conversion of arginines to citrullines) were located in loop regions and thus accessible to modifying enzymes. The triproline segment (residues 99-101) is fully exposed on the back surface of the protein in a long crossover connection between two parallel beta-strands. The proximity of this region to the underlying beta-sheet suggests that post-translational modifications here might have potential synergistic effects on the entire structure. Post-translational modifications that lead to a reduced surface charge could result first in a weakened attachment to the myelin membrane rather than in a gross conformational change of the protein itself. Such mechanisms could be operative in demyelinating diseases such as multiple sclerosis.

Energetic approach to the folding of α/β barrels

The folding of a polypeptide into a parallel (alpha/beta)8 barrel (which is also called a circularly permuted beta 8 alpha 8 barrel) has been investigated in terms of energy minimization. According to the arrangement of hydrogen bonds between two neighboring beta-strands of the central barrel therein, such an alpha/beta barrel structure can be folded into six different types: (1) left-tilted, left-handed crossover; (2) left-tilted, right-handed crossover; (3) nontilted, left-handed crossover; (4) nontilted, right-handed crossover; (5) right-tilted, left-handed crossover; and (6) right-tilted, right-handed crossover. Here "tilt" refers to the orientational relation of the beta-strands to the axis of the central beta-barrel, and "crossover" to the beta alpha beta folding connection feature of the parallel beta-barrel. It has been found that the right-tilted, right-handed crossover alpha/beta barrel possesses much lower energy than the other five types of alpha/beta barrels, elucidating why the observed alpha/beta barrels in proteins always assume the form of right tilt and right-handed crossover connection. As observed, the beta-strands in the energy-minimized right-tilted, right-handed crossover (alpha/beta)8-barrel are of strong right-handed twist. The value of root-mean-square fits also indicates that the central barrel contained in the lowest energy (alpha/beta)8 structure thus found coincides very well with the observed 8-stranded parallel beta-barrel in triose phosphate isomerase (TIM). Furthermore, an energetic analysis has been made demonstrating why the right-tilt, right-handed crossover barrel is the most stable structure. Our calculations and analysis support the principle that it is possible to account for the main features of frequently occurring folding patterns in proteins by means of conformational energy calculations even for very complicated structures such as (alpha/beta)8 barrels.

Energy of stabilization of the right-handed βαβ crossover in proteins

An explanation in terms of conformational energies is provided for the observed nearly exclusive preference of the βαβ structure for forming a right-handed, rather than a left-handed, crossover connection. Conformational energy computations have been carried out on a model βαβ structure, consisting of two six-residue Val β-strands and of a 12-residue Ala α-helix, connected by two flexible four-residue Ala links to the strands. The energy of the most favorable right-handed crossover is 15.51 kcal/mol lower than that of the corresponding left-handed cross-over. The right-handed crossover is a strain-free structure. Its energy of stabilization arises largely from the interactions of the two β-strands with one another and with the α-helix. On the other hand, the left-handed crossover is either disrupted after energy minimization or it remains conformationally strained, as indicated by an energetically unfavorable left twisting of the β-sheet and by the presence of high-energy local residue conformations. In the energetically most favorable right-handed crossover, the right twisting of the β-sheet and its manner of interacting with the α-helix are identical with those computed earlier for isolated β-sheets and for packed α β structures. This result supports a proposed principle that it is possible to account for the main features of frequently occurring structural arrangements in globular proteins in terms of the properties of their component structural elements.