U-shaped Cavity Research Articles

A study of space charge measurement

Abstract At present, there is no appropriate measurement techniques for space charge. In this paper, a U-shaped cavity device is developed as the space charge measurement device, which can be applied to transmission lines. Its design principle and calculation techniques of design parameter are also introduced. To test the space charge measurement accuracy of the U-shaped cavity device, a space charge generator is developed specifically for this experiment. The test results are excellent and show that the U-shaped cavity device can meet the design requirements. This technique is suitable for space charge measurement under transmission line normally charged work condition.

Design of Conformal Helical Antenna with Selective Bands

The paper presents design of U-shaped partial cavity which backs a 11⁄2 turn helical antenna. The antenna is operating between C-Ku bands. Various selective resonant bands are achieved by varying the orientation of helix with respect to the walls inside the designed cavity and thus making the design reconfigurable in nature. The antenna has a highest bandwidth of 2.77 GHz and a peak gain of 10.8 dB.

Highly efficient single longitudinal mode-pulsed green laser

A novel design for a highly ecient 1-kHz single-frequency green laser is proposed. An ecient single-frequency laser pulse output at 532-nm wavelength may be obtained by combining the injection seeding with intracavity frequency doubling in a compact U-shaped cavity formed by two plano dichroic mirrors in an end-pumping arrangement. The laser is capable of producing green pulses with a total energy of 6.3 mJ at a pulse repetition rate of 1 kHz. The pulse width is about 10 ns and the optical-optical eciency from the 808-nm pump source to the 532-nm green output is around 12.7%.

Enhancement of natural convection heat transfer in a U-shaped cavity filled with Al2O3-water nanofluid

This paper investigates the natural convection heat transfer enhancement of Al2O3-water nanofluid in a U-shaped cavity. In performing the analysis, the governing equations are modeled using the Boussinesq approximation and are solved numerically using the finite-volume numerical method. The study examines the effects of the nanoparticle volume fraction, the Rayleigh number and the geometry parameters on the mean Nusselt number. The results show that for all values of the Rayleigh number, the mean Nusselt number increases as the volume fraction of nanoparticles increases. In addition, it is shown that for a given length of the heated wall, extending the length of the cooled wall can improve the heat transfer performance.

Fabrication of Metallic Split-Ring Arrays for Metamaterials Using Silica Particle Templates Anchored on a Silicon Substrate

In this paper, we rely on the formation of novel macroporous polystyrene (PS)/silica masks to prepare two-dimensional (2D) arrays of metallic split ring (SR) and full ring (FR) microstructures on silicon substrates. In these PS/silica porous templates, 2D silica particle arrays were made to anchor on silicon wafers on which PS membranes with 2D pore arrays are molded and made movable via a fluid flow perturbation after partial etching of the silica particles. By using the porous masks in combination with physical deposition, both metallic FRs and SRs on silicon substrates can be prepared. The obtained SRs have a nearly U-shaped cavity and a circular outer profile. The present method could open an alternative but low-cost and parallel approach for obtaining artificial magnetic metamaterials operating in near infrared.

Competing Electron-Transfer Pathways in Hydrocarbon Frameworks: Short-Circuiting Through-Bond Coupling by Nonbonded Contacts in Rigid U-Shaped Norbornylogous Systems Containing a Cavity-Bound Aromatic Pendant Group

This work explores electron transfer through nonbonded contacts in two U-shaped DBA molecules 1DBA and 2DBA by measuring electron-transfer rates in organic solvents of different polarities. These molecules have identical U-shaped norbornylogous frameworks, 12 bonds in length and with diphenyldimethoxynaphthalene (DPMN) donor and dicyanovinyl (DCV) acceptor groups fused at the ends. The U-shaped cavity of each molecule contains an aromatic pendant group of different electronic character, namely p-ethylphenyl, in 1DBA, and p-methoxyphenyl, in 2DBA. Electronic coupling matrix elements, Gibbs free energy, and reorganization energy were calculated from experimental photophysical data for these compounds, and the experimental results were compared with computational values. The magnitude of the electronic coupling for photoinduced charge separation, /V(CS)/, in 1DBA and 2DBA were found to be 147 and 274 cm(-1), respectively, and suggests that the origin of this difference lies in the electronic nature of the pendant aromatic group and charge separation occurs by tunneling through the pendant group, rather than through the bridge. 2DBA, but not 1DBA, displayed charge transfer (CT) fluorescence in nonpolar and weakly polar solvents, and this observation enabled the electronic coupling for charge recombination, /V(CR)/, in 2DBA to be made, the magnitude of which is approximately 500 cm(-1), significantly larger than that for charge separation. This difference is explained by changes in the geometry of the molecule in the relevant states; because of electrostatic effects, the donor and acceptor chromophores are about 1 A closer to the pendant group in the charge-separated state than in the locally excited state. Consequently the through-pendant-group electronic coupling is stronger in the charge-separated state--which controls the CT fluorescence process--than in the locally excited state--which controls the charge separation process. The magnitude of /V(CR)/ for 2DBA is almost 2 orders of magnitude greater than that in DMN-12-DCV, having the same length bridge as for the former molecule, but lacking a pendant group. This result unequivocally demonstrates the operation of the through-pendant-group mechanism of electron transfer in the pendant-containing U-shaped systems of the type 1DBA and 2DBA.

Numerical analysis of unsteady behavior of cloud cavitation around a NACA0015 foil

Three-dimensional unsteady cavitating flow around a NACA0015 hydrofoil fixed between the sidewalls was simulated and the mechanism of U-shaped cloud cavity formation was clarified. A local homogeneous model was used for the modeling of the vapor–liquid two-phase medium. The compressible two-phase Navier–Stokes equations as the governing equations were solved. To describe the phase change between water and vapor, the mass transfer model based on the theory of evaporation/condensation on a plane interface was introduced. The cell-centered finite volume method was employed to discretize the governing equations. Assuming turbulent flow, the turbulent eddy viscosity coefficient was computed by using the Baldwin–Lomax model with the Degani–Schiff modification. As a result, even in the case of cavitating flow without sidewalls, the shed cloud cavities has slightly 3D structure, which was not so much large as extending across the whole spanwise direction. On the other hand, in the case of cavitating flow with sidewalls, the end of sheet cavities bows in the spanwise direction because of the development of boundary layer near both sidewalls. After that, due to the occurring of the reentrant jet towards the mid-span region, the sheet cavities breaks off from mid-span region near the leading edge of the hydrofoil, and became the vortical cloud cavities, which have the large-scale U-shaped structure.

Probing the dimensions of semi-rigid inner functionalised U-shaped bis-porphyrin cavities

The synthesis of a series of open U-shaped bis-porphyrin cavity molecules is described, with bridged bicyclic backbones to confer rigidity, and a pendant substituted aromatic probe unit suspended on the inside of the cavity. The dimensions and flexibility of the bis-zincporphyrin cavity were probed using several different techniques. Initially the molecular ruler concept was employed, using flexible bidentate ligands as guests with a range of possible linear dimensions. Secondly, NMR methods were employed with rigid bidentate ligand guests of fixed lengths, and thirdly diffusion based NMR methods were utilised. The range of inter-porphyrin distances estimated by these methods suggests that these types of open-cavity systems have a surprising degree of flexibility.

The Design of Inner-Functionalised U-Shaped Cavity Molecules: Role of Phenyl Substituents at the 1,3-Position of Isobenzofurans and Oxa-Bridges in the Dienophile as Stereochemical Controlling Elements

1,3-Diphenylisobenzofuran reacts with fused mono- and bis-norbornenes, 7-oxanorbornenes and cyclobutene-1,2-diesters with high stereospecifity whereas the corresponding isobenzofuran cycloadditions produce mixtures; this provides a basis for regulating geometry in the construction of polyalicyclic nanostructures.

Acute complete nonpuerperal uterine inversion

Nonpuerperal uterine inversion is a rare entity. Diagnosis is difficult because of the rarity of the condition and is often made at the time of surgery (1). A case of acute complete nonpuerperal uterine inversion with successful operative management is presented. A 41-year-old woman was referred to our hospital for lower abdominal pain and profuse vaginal bleeding of 8 h duration, palpation of a vaginal mass and anemia [hemoglobin (Hb) = 6.1 mg/dL]. She had already been transfused with four units of blood. Her medical history consisted of two previous cesarean sections, 14 and 12 years ago, and a uterine leiomyoma of size approximately 5 cm diagnosed 9 months ago after an episode of menorrhagia, but she had had no symptoms or complaints since then. Initial examination confirmed these findings and we found an Hb concentration of 8.4 mg/dL. The patient was immediately transferred to the operating theatre, suspecting that the cause was an expelled leiomyoma. Attempts at vaginal excision of the mass protruding into the vagina were unsuccessful and bleeding was heavy. Furthermore, neither the cervix nor the uterus could not be palpated. An immediate laparotomy was performed, revealing a complete inversion of the uterus. The bladder fundus, the adnexal structures, such as the fallopian tubes and round ligaments, accompanied the inversion and the ovaries were barely visible in the opening produced by it. Numerous attempts at bimanual reversion of the uterus were unsuccessful and a Haultain procedure was performed, making a midline incision of the posterior uterine inversion ring between the uterosacral ligaments, and performing gradual reversion of the uterus with the fundal leiomyoma. A total hysterectomy was performed to stop the bleeding. The patient received another three units of whole blood and had an Hb concentration of 7.8 mg/dL by the end of the operation. The postoperative period was uneventful and she was discharged on the fifth postoperative day in good condition. Nonpuerperal uterine inversion is a rare entity and its incidence has not been estimated in the literature (2, 3). It is classified as acute or chronic and subclassified as incomplete (fundus protrudes into the uterine cavity but not through the external cervical os), complete (fundus protruding through the external cervical os) or total (inversion of the uterus and part of or the entire vagina) (4). A previous cesarean section has been implicated as a risk factor for puerperal uterine inversion (5). Nonpuerperal inversions occur due to a tumor or an idiopathic event. Most tumors are reported to be uterine leiomyomas and the mechanism involved is thought to be the distension of the cavity, weakening of the uterine walls and the expulsive contractions of the uterus and weight of the tumor itself (4). In idiopathic cases the condition is usually abrupt, accompanied by pain and shock, while in tumor-produced cases it is mostly associated with chronic vaginal discharge and irregular vaginal bleeding (4). This, however, was not the case in our patient in whom a tumor-produced inversion caused the acute onset of lower abdominal pain and profuse vaginal bleeding leading to significant blood loss. Diagnosis can be difficult and two criteria must be applied on clinical examination: 1) nonvisualization of the cervix after excision of the vaginal mass; and 2) nonpalpation of the uterine corpus in bimanual examination with an empty bladder (3). Sonographic characteristics for incomplete inversion are the poor delineation of the endometrial stripe with a Y-shaped configuration (3). Computed tomography diagnosis may be difficult, but nonvisualization of the uterus in the pelvis and visualization of edematous endometrium and myometrium in the middle pelvis are suggestive of the condition (3). Magnetic resonance imaging (MRI) has been used recently for the diagnosis of uterine inversion where the U-shaped cavity may be seen (1). Four surgical procedures (two vaginal and two abdominal) have been used for the treatment of this condition (1, 4). The abdominal Haultain procedure, which consists of incising the constriction ring posteriorly followed by reversion of the uterus, was used successfully in our case. This procedure seems to be safe and effective in reducing the risks of bladder and ureter injury, and is also the procedure of choice in the case of malignant tumors causing the uterine inversion (1).

Organometallic supramolecular chemistry with monosaccharides: triethylammonium mu-chloro-bis[chloro(eta5-cyclopentadienyl)-(methyl 4,6-o-benzylidene-beta-D-glucopyranosidato-1kappaO2,1:2kappaO3) zirconate

The reaction of [CpZrCl3(thf)2] with methyl 4,6-O-benzylidene-beta-D-glucopyranoside (beta-MeBGH2, 1) in the presence of Et3N results in the formation of the zirconate complex [Et3NH] [(CpZrCl)2(mu-Cl) (mu-(beta-MeBG)]2] (2). X-ray structure analyses were performed from the ligand precursor beta-MeBGH2 1 as well as from 2. Compound 1 crystallizes in the monoclinic chiral space group P2(1). The molecules show a flat arrangement including the benzylidene protecting group, and are packed in columns. The columns are held together in pairs by the formation of hydrogen bonds between the hydroxy functions in positions 2 and 3. Compound 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1). The beta-MeBG ligands are chelating the Zr atoms through the oxygen atoms in positions 2 and 3 of the glucopyranosidato ligand revealing a 1-zircona-2,5-dioxolane moiety each; the oxygen atom in position 3 is linked to both of the Zr atoms. Additionally one chloro ligand is bridging the two Zr centers. Two terminally bound chloro ligands stick out from the two Zr atoms into a chiral U-shaped cavity constructed by the two beta-MeBG ligands. The cavity incorporates the tertiary ammonium cation [Et3NH]+ which is bound to one of the terminal chloro ligands through a hydrogen bond. The inclusion of the [Et3NH]+ cation in the U-shaped cavity, even in solution, is demonstrated by NMR spectroscopic data.

L'âne de Buridan, le principe de Curie et l'effet-cheminée. Courant d'air dans les cavités en forme de U

The Buridan's donkey ; the principle of curie and the chimney effect (air flow in u-shaped cavity). In a U shaped cave there is an air flow in winter. This phenomenon is a beautiful exemple of physical broken symmetry. In summer, it is possible to observe a pendulum oscillation of cold air in a U-shaped cavity.

An Adduct Between Tetraammine(1,10-phenanthroline)ruthenium(II) and Dibenzo-42-crown-14

The crystal structure of the adduct dibenzo-42-crown-14 (OC-6-22)-tetraammine(1,10-phenanthroline-N,N')-ruthenium(II) bis(hexafluorophosphate) dichloromethane solvate, [Ru(C 12 H 8 N 2 )(NH 3 ) 4 ] (PF 6 ) 2 .C 36 H 56 O 14 .CH 2 Cl 2 , is reported. The guest Ru complex is located deep within the U-shaped cavity formed by folding of the flexible crown host. The ammine ligands of the Ru complex participate in an extensive network of hydrogen bonds with the ether O atoms of the crown. Weak π stacking appears to occur between the aromatic rings of the phenanthroline ligand and the benzene groups of the crown ether.

Fundamental Principles of BLOCK Design and Assembly in the Production of Large, Rigid Molecules with Functional Units (Effectors) Precisely Located on a Carbocyclic Framework

New cycloaddition reactions have been developed to regiospecifically couple together alicyclic reagents (blocks) containing the same or different functional units (effectors). Dipolar cycloadditions (alkenes plus cyclobutene epoxides and the related aziridines), Diels-Alder cycloadditions (alkenes plus dienes formed from s-tetrazine, 1,2,4-triazine and 1,3,4-oxadiazole) and condensations of α-diones with vic-diamines have been used as the coupling procedures. This new approach is based on a building block strategy where small blocks already containing an attached effector are joined in a simple convergent step to produce large rigid structures (ribbon molecules) containing one or more effector groups precisely positioned both in distance and relative orientation onto an inert carbocyclic frame (a molrac). These effector groups include porphyrins, crown ethers, fluorophores, nucleic acid bases, β-lactams, redox-active components, bidentate ligands of various type, amino acids, intercalators, and metal complexes. All these classes can be joined together either as homo or mixed pairs into rods, spacers or U-shaped cavity structures, whose shapes can be evaluated using molecular modelling (AM1, Sybyl, PM3 etc.).

The synthesis of U-shaped cavity molecules with “inner-surface” functionality

Abstract New U-shaped cavity molecules with inner-surface functionalisation, eg 19 and 20 , have been prepared by stereoselective reaction of cyclopentadiene onto linear bis -(7-oxanorbornenes) 18 and 17 respectively. The norbornene π-centres of cavity molecules 19, 20 are reacted with DMAD/Ru to yield rigid bis -cyclobutenes 21 and 22 which serve as a common entry point to advanced cavity systems with further inner-surface functionalisation (CO, O, alkene). This is achieved by reaction of 21 or 22 with appropriate cyclic dienes (cyclopentadienones, isobenzofurans, furan and 6,6-dimethylfulvene) in highly specific cycloaddition reactions.

Coupling strength dependence of phase locking of Ar-ion lasers

An experiment was performed using two cw Ar-ion lasers in Fabry-Perot resonators configured in a U-shaped cavity and coupled through a common end mirror to examine the effect of coupling strength on phase locking. The near field fringe visibilities were measured while varying the reflectivity of the common end mirror from 10 to 90%. The total multiline and single line visibilities during multiline coupling along with the visibility during single line coupling were measured. The optimal coupling strength for phase-locked operation for the Ar-ion lasers used in this experiment was found to be ~25%.