Pinch Structures Research Articles

Development of novel rectal/uterine clamping device

We developed a novel clamping device for laparoscopic surgery, free from conventional pinch structure, capable of uniformly occluding any ductal organ. This study aimed to evaluate performance of the new clamper compared to the pinch-type clamper. The new clamper consists of two metal bars with ties at each end, which enables parallel clamping. A resected porcine stomach was used, with an infusion tube at the anal end to increase intra-luminal pressure. The oral side of the stomach was clamped with either the new clamper or the pinch-type clamper, and their performances were evaluated in qualitative and semi-quantitative manner. Qualitative evaluation involved imaging the clamping site at intra-gastric pressures from 0 to 15 mmHg using microfocus computed tomography. The new clamper showed no gap even under increased intra-luminal pressure, while the pinch-type clamper showed a gap on the distal side. Quantitative evaluation measured bursting pressure under continuous air insufflation. Air leakages were observed in the new clamper at higher intra-luminal pressures than in the pinch-type clamper (46.1 mmHg vs. 13.6 mmHg, P < 0.01). Our new clamping device showed superior performance in preclinical setting compared to the conventional pinch-type clamper. We are currently working on its design freezing and aiming for early commercialization.

Optimised coker unit design integrating heat exchange network and exergy analysis

Two approaches are applied for reducing energy consumption in an actual delayed coking plant converting vacuum residue into lighter and higher value hydrocarbon products. Pinch analysis is applied with a view to optimising the pinch temperature approach and structure of the existing seven heat exchangers' network. This resulted in about 27% reduction of the total annual cost corresponding to an annual saving of about US$1.9 million. Exergy analysis is also conducted on other main process plant equipment which revealed a possible annual saving of US$0.75 million through generation of medium pressure steam in the blowdown tower.

Does second phase content control the evolution of olivine CPO type and deformation mechanisms? A case study of paired harzburgite and dunite bands in the Red Hills Massif, Dun Mountain Ophiolite

We have examined the microstructures and crystallographic preferred orientations (CPOs) of six “paired” harzburgite and dunite samples from a small (~ 1 km2) area in the Ellis Stream Complex, Red Hills Massif, Dun Mountain ophiolite belt in New Zealand. Here, banded peridotites with isoclinal folds, E-W striking vertical foliations and vertical lineations are inferred to result from shear on vertical planes that overprint previous mantle structures. The samples contain five different olivine CPOs: typically known as A, C, D, E and AG-types. The co-located harzburgite and dunite of each pair show different CPOs (e.g., A vs E type). In each pair, dunite generally has larger grain size and stronger CPO. At two localities, the dunite has layers with different CPOs (A and D/E types) and grain sizes, corresponding to variations in spinel content. Paired samples were collected from nearby (a few cm maximum) parallel layers with no pinch and swell structures to suggest strain partitioning and dynamically recrystallized grain long axes parallel to lineation in both. Thus we infer that the deformation conditions (e.g., temperature, pressure) and kinematics were the same for the harzburgite and dunite in each pair. It is most feasible that second phase content (orthopyroxene and/or spinel) is the primary factor controlling the CPO type at a single locality. Additionally, we observed a change of the CPO types and a decrease in CPO strength from the eastern to the western part of the Ellis Stream Complex. We infer this relates to decreasing strain. The different CPOs of harzburgites and dunites suggest that the second phase content exerts a significant control on olivine CPO development.

Effect of insulator surface conditioning on the pinch dynamics and x-ray production of a Ne-filled dense plasma focus

The dense plasma focus (DPF) can be an intense source of x rays, wherein the insulator sleeve strongly dictates the electrical breakdown, which subsequently affects the formation of a plasma sheath and a collapse phase. Experiments on a 25 kJ DPF (operated at 4.4 kJ) are carried out to demonstrate the influence of insulator surface morphology on the pinch structure, dynamics, and x-ray yield using a Ne fill. Two borosilicate insulators are directly compared, one with a smooth finish and the other machined with four circumferential grooves traversing the perimeter of the exterior insulator surface. Comparisons are made through same-shot imaging diagnostics of the evolving plasma sheath during breakdown, rundown, and at the pinch in addition to the time-resolved measurements of emitted x rays via filtered photodiodes. The presence of structures on the insulator sleeve reduces x-ray production across all fill pressures by a factor of 2.8 ± 2.4 on average and reduces the highest x ray producing shots by a factor of 5.5 ± 1.8. Observations of sheath asymmetry and inhomogeneity at lift-off are observed and correlated with subsequent observations of off-axis radial collapse. Taken together, this suggests that local variations in the insulator surface decrease the spatial uniformity of the sheath, leading to an azimuthally asymmetric focus, reduced electron densities, and, ultimately, degraded x-ray production.

High Pressure in Boron Nitride Nanotubes for Kirigami Nanoribbon Elaboration

Cutting and folding 2D systems is one of the explored paths to tune physical and chemical properties in one-atom-thick matter. Contrary to graphene, boron nitride (BN) nanoribbons are difficult to obtain, and folded BN nanoribbon structures have not been reported yet. Here, we show that pressure application in multiwalled boron nitride nanotubes leads to different types of tube internal organizations including BN nanoribbon formation and folds. The new structures are associated with the breaking of a number of the internal tubes, leading to either nonorganized structures in the form of internal tube alveoli or an organized stacking of folded h-BN nanoribbons. Irreversible changes in the morphology of multiwalled BN nanotubes (MWBNNTs) take place from ∼7 GPa, and morphologically modified tubes could be observed up to pressures of at least 49 GPa. The experimental probes utilized included high-resolution transmission microscopy, electron tomography, and Raman spectroscopy. Atomistic modeling shows the formation of pinch structures along the tubes that favor pressure-induced bond-breaking and hybridization changes and confirm the folded structure. Both experiments and modeling show that tube polygonization is a prominent characteristic of MWBNNTs even at ambient pressure. Overall, the pressure evolution of MWBNNTs strongly differs from their carbon analogues. The high mechanical stability of BN tube geometry is of interest for composite-based structural materials. On the other side, the availability of h-BN nanoribbons and folded structures opens new prospects to produce physically modified BN properties.

ALE-MHD technique for modeling three-dimensional magnetic implosion of a liner

The article is devoted to the methodology for modeling current-carrying plasma in a Z-pinch studied in pulsed-power experiments. We discuss simulation performed via moving Lagrangian-Euler difference grid. The difference scheme approximating the hydrodynamic equations of a high-temperature medium possesses a “complete conservation” property and includes energy balances between the plasma components taking into account electromagnetic field – matter interaction and conductive (electronic, ionic) as well as radiative heat transfer. Numerical experiments provide quantitative estimates of physical effects which lead to essential distortions of a plasma shell during its magnetically-driven implosion. Performed simulations show the effect of instabilities on the final pinch structure, mainly, the hydrodynamic Rayleigh-Taylor instability and instability of a temperature-inhomogeneous plasma

Mineralogy, geochemistry, and genesis of the volcanic-hosted hydrothermal iron ore deposit in Somea, NW Iran

The Somea iron deposit is located ~ 22 km northwest of Ahar, NW Iran. The lenticular iron ores are formed as open space fillings within the pinch and swell structures of a curved fault in a highly brecciated zone within the host andesitic to dacitic rocks. Fe mineralization comprises magnetite and pyrite in the hypogene zone and hematite, limonite, and goethite in the supergene zone. According to the geochemical analysis results, the average grade of Fe ore is about 53 wt%. Magnetite ore is massive and lenticular in shape. Pyrite is formed as veins/veinlets in the crushed zones and fractures within the magnetite ore, following the continued tectonic movements along the fault. Goethite displays spongy and box-work, as well as botryoidal and colloform textures. Spongy and box-work textures indicate the very high acidity of the leaching fluids, which may be resulted from the oxidation of pyrite veins/veinlets. Banded and colloform textures are produced by colloidal precipitation from fluids. Hematite has formed either due to the alteration of magnetite or by dehydration of goethite at the oxidized zone. The very high Fe/Mn ratio of ore samples may indicate the hypogene genesis of the ore-bearing fluids, which were most likely originated from the neighboring Sheyvardagh granitic–granodioritic intrusion. Sulfur isotopic composition of the pyrite samples reveals a magmatic origin for the ore-bearing fluid and its sulfur content, which further advocates the hydrothermal genesis of the ore body. The δ34S values of the pyrite separates are ranging between − 1.4 and − 0.69‰ (V-CDT).

Determining relative bulk viscosity of kilometre-scale crustal units using field observations and numerical modelling

Though the rheology of kilometre-scale polymineralic rock units is crucial for reliable large-scale, geotectonic models, this information is difficult to obtain. In geotectonic models, a layer is defined as an entity at the kilometre scale, even though it is heterogeneous at the millimetre to metre scale. Here, we use the shape characteristics of the boundaries between rock units to derive the relative bulk viscosity of those units at the kilometre scale. We examine the shape of a vertically oriented ultramafic, harzburgitic-lherzolitic unit, which developed a kilometre-scale pinch and swell structure at mid-crustal conditions (~600°C, ~8.5kbar), in the Anita Shear Zone, New Zealand. The ultramafic layer is embedded between a typical polymineralic paragneiss to the west, and a feldspar-quartz-hornblende orthogneiss, to the east. Notably, the boundaries on either side of the ultramafic layer give the ultramafics an asymmetric shape. Microstructural analysis shows that deformation was dominated by dislocation creep (n=3). Based on the inferred rheological behaviour from the field, a series of numerical simulations are performed. Relative and absolute values are derived for bulk viscosity of the rock units by comparing boundary tortuosity difference measured on the field example and the numerical series. Our analysis shows that during deformation at mid-crustal conditions, paragneisses can be ~30 times less viscous than an ultramafic unit, whereas orthogneisses have intermediate viscosity, ~3 times greater than the paragneisses. If we assume a strain rate of 10−14s−1 the ultramafic, orthogneiss and paragneiss have syn-deformational viscosities of 3×1022, 2.3×1021 and 9.4×1020Pas, respectively.Our study shows pinch and swell structures are useful as a gauge to assess relative bulk viscosity of rock units based on shape characteristics at the kilometre scale and in non-Newtonian flow regimes, even where heterogeneity occurs within the units at the outcrop scale.

Shape of pinch and swell structures as a viscosity indicator: Application to lower crustal polyphase rocks

Pinch and swell structures occur where a more competent layer in a weaker matrix is subjected to layer-parallel extension. In this contribution, we use numerical models to explore the use of pinch and swell structure shape symmetry and asymmetry as a determinant of relative viscosity between layers. Maximum asymmetry is attained when the matrix viscosity on one side is subtly weaker than the competent layer, while the other side is significantly weaker.Our numerical results are directly applied to asymmetrically developed pinch and swell structures in exposed lower continental crust. Here, shape geometries observed in a shear zone comprised of plagioclase-dominated, garnet-dominated and mixed amphibole-plagioclase-dominated bands, reveals that the plagioclase-dominated band is the most competent band and is marginally stronger (2×) and significantly stronger (10–40×) than the fine grained garnet-dominated and mixed amphibole-plagioclase-dominated band, respectively. Based on the experimentally determined viscosity of a plagioclase-dominated material and quantitative microstructural analysis, the viscosity range of the natural rock bands is 2.8 × 1015 to 1.1 × 1017 Pa s. Consequently, the assumption that the experimentally-derived plagioclase flow law is an appropriate proxy for the middle to lower continental crust may lead to a viscosity over-estimation by up to forty times.

Pinch and swell structures: evidence for strain localisation by brittle–viscous behaviour in the middle crust

Abstract. The flow properties of middle crustal rocks are commonly represented by viscous flow. Examples of pinch and swell structures found in a high strain zone at St. Anne Point (Fiordland, New Zealand) and Wongwibinda (N.S.W., Australia) suggest pinch and swell structures may be initiated by brittle failure of the more competent layer in conjunction with subsequent material softening. On this basis we develop a numerical model where Mohr–Coulomb constitutive strain localising behaviour is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow, provided the competent layer has sufficient viscosity contrast and can localise strain to form shear bands. The flow regime and strain localising characteristics of the surrounding country rock appear not to impact pinch and swell structure formation. The degree of material softening after the initial strain localising behaviour is shown to impact pinch and swell characteristics, while extensive material softening causes the formation of thick necks between swells by limiting the focused localisation of strain into shear bands. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr–Coulomb strain localising behaviour combined with viscous flow is a viable alternative representation of the heterogeneous rheological behaviour of rocks seen in the middle crust. This type of mid-crustal rheological behaviour can have significant influence on the localisation of strain at all scales. For example, inclusion of Mohr–Coulomb strain localising behaviour with viscous flow in just some mid-crustal layers within a crustal-scale model can result in significant strain localisation, extending from the upper crust into the middle crust. This localisation also influences the development of near-surface structures.

Soft x-ray studies of plasma-focus pinch structures in PF-1000U experiments

This work reports on recent experiments performed at the modernized PF-1000U plasma-focus facility. In contrast to earlier studies the main attention was focussed on measurements of the soft x-ray emission. Detailed time-integrated x-ray measurements, carried out using filtered pinhole cameras with sensitive x-ray films, are presented and analysed. The fine structure of the collapsing current sheath and dense pinch column is investigated. Observations of ‘plasma filaments’ are discussed and compared with those from the old POSEIDON facility. New results are time-integrated x-ray images of PF-1000U discharges with additional gas puffing, which in many cases show distinct plasma filaments and/or ‘hot spots’ formed inside the dense pinch column. The formation of such ‘hot-spots’ is explained by necking and breaking of the plasma filaments. Results of time-resolved x-ray measurements, performed outside the experimental chamber by means of scintillation probes, and inside with PIN-diodes placed behind pinholes and absorption filters, are also presented Time-resolved measurements, carried out using an old XUV framing-camera and a new soft x-ray four-frame camera (SXRFFC), are also presented and discussed. Correlations of the time-integrated x-ray images (of plasma filaments and hot spots) with time-resolved x-ray signals are discussed. The hypothesis that plasma-current filaments appear in almost all PF-type discharges is supported by pictures of radial erosion tracks on the anode front-plate after many discharges.

Influence of the external magnetic field on pinch evolution and neutron production in plasma-focus discharge

In this paper, the results of the study of the influence of the applied external axial magnetic field on the dynamics of pinch and neutron production are presented, following from measurements using x-ray, interferometry and neutron diagnostics performed on the plasma-focus PF-1000 device with deuterium as the filling gas at the current of 2 MA and neutron yield above 1010. The permanent magnets with a magnetic field of a few hundredths of tesla were used both inside the anode body and in front of the end of the dense column. This magnetic field decreases the neutron yield, depresses the implosion velocity and the velocity of the transformations of internal structures, stabilizes the pinch column, increases its axial symmetry and indirectly confirms the existence of internal closed currents inside the pinch structures.

Effect of anode shape on pinch structure and X-ray emission of plasma focus device

The effect of anode shapes on pinch structure and X-ray emission of plasma focus device operated with cylindrical, diverging, oval and converging anode tips is reported. The pinch structure in the radial compression phase has been investigated by employing a triple pinhole camera. It has been observed that pinch structure as well as the X-ray emission of PF device strongly depends upon anode tip designs. For the first time the studies were carried out in two new shapes of anode tips that is the oval and the divergent one. It has been observed that the oval and diverging anode tips are more conducive for the formation of instabilities and hotspot generation. The studies of X-ray emission were also carried out by employing three channels of a p-i-n diode X-ray spectrometer in entire anode designs to corroborate the results of a triple pinhole camera. Additionally, the effective hard X-ray photon energy was also estimated by the radiography method for all the anode tip designs, which indirectly provide a qualitative idea of the generation of induced accelerating field in the pinched column during compression.

Petrologic and Structural Features of Basement Rocks of Parts of Mukuru Area, Southeastern Nigeria

Field investigations in the western part of Mukuru area indicate intense structural imprints and high HT/HP metamorphism, and some magmatism. The rock units in the area include migmatitic gneisses, granulites, amphibolites, schists, charnockites, epidiorites and granites. The charnockites which are common in the shear zone and boundary areas appear to mark the end of magmatism. However, relicts of magmatic rocks mapped at Ubong Community in the study area suggest earlier magmatism. The metamorphic rocks are strongly deformed in a N-S to NE-SW direction with ghost structures, pinch and swell structures, ptygmatic veins, showing evidence of extensional tectonics. No visible contact relationship between the migmatitic gneisses and schists was observed. Diagnostic metamorphic structures like fine banding/layering of alternating dark- and light-coloured layers are conspicuous in gneisses and some amphibolites while schistosity and deep weathering are present in schists. The geodynamic features prevalent in Mukuru area are deformation and metamorphism. They indicate a possible petrogenetic link to southern Obudu Plateau in the north, western Cameroon in the east than Bansara in the west.

MAGNETIC FIELD STRUCTURE AROUND LOW-MASS CLASS 0 PROTOSTARS: B335, L1527, AND IC348-SMM2

We report new 350 μm polarization observations of the thermal dust emission from the cores surrounding the low-mass, Class 0 young stellar objects L1527, IC348-SMM2, and B335. We have inferred magnetic field directions from these observations and have used them together with results in the literature to determine whether magnetically regulated core-collapse and star formation models are consistent with the observations. These models predict a pseudo-disk with its symmetry axis aligned with the core magnetic field. The models also predict a magnetic field pinch structure on a scale less than or comparable to the infall radii for these sources. In addition, if the core magnetic field aligns (or nearly aligns) the core rotation axis with the magnetic field before core collapse, then the models predict the alignment (or near alignment) of the overall pinch field structure with the bipolar outflows in these sources. We show that if one includes the distorting effects of bipolar outflows on magnetic fields, then in general the observational results for L1527 and IC348-SMM2 are consistent with these magnetically regulated models. We can say the same for B335 only if we assume that the distorting effects of the bipolar outflow on the magnetic fields within the B335 core are much greater than for L1527 and IC348-SMM2. We show that the energy densities of the outflows in all three sources are large enough to distort the magnetic fields predicted by magnetically regulated models.

An Alternative Concept for the Structure of an X-Ray Emitting $Z$-Pinch

We propose a more nuanced view of the structure of the X-ray emitting plasma in a Z -pinch. There are four relevant observations. First, in K-shell emitting Z -pinches, K-shell pulsewidth and K-shell pinch diameter seem linearly correlated. Second, on a given generator, peak K-power is not strongly correlated with the K-yield. Third, we sometimes see very narrow ?filaments? (as small as 100-?m in diameter, using a camera based on digital imaging plates) of intense K-shell emission that can extend for over a centimeter axially. Yet, on most shots, the observed pinch structure is quite amorphous; pinches with large average diameter show the least structural detail. Fourth, power flow losses upstream of the pinch within 10 ns of the start of K emission correlate with reduced K-yield. These observations can be reconciled if apparent pinch ?diameter? is actually due to the transverse (radial) motion of the filaments. That is, the filaments are kink unstable, with transverse velocity on the order of ~ 40 cm/?s (in argon). Hence, a large pulsewidth pinch shows no filaments because time-integrated pinhole images are blurred by motion of the filament(s). Thus, the basic K radiating ?elements? of a pinch are a few thin (~ 0.1 mm), long (few millimeters), and high-density filaments that can propagate for many millimeters axially. Each filament radiates at a relatively fixed peak power. Implied ion densities in a filament are > 1020 /cm3 with actual temperatures that are well below values commonly reported (> 1.5 keV). Overall, yield will depend on the duration of the pinch which is due to the lifetime of the filament(s) rather than a transit time based on a ?sound speed.? The continued push from the magnetic field controls the filament lifetime. Hence, late time power flow losses can reduce the field and hence the filament lifetime and the K-yield. This interpretation of a pinch is in contrast to the notion of a many-millimeter-wide column of hot plasma that simply radiates away the energy that was accumulated during the implosion.

10.1007/s11450-008-3006-3

The results of experiments devoted to studying the generation of MeV photons and protons in picosecond laser plasmas at a laser beam intensity of 1018 W/cm2 on Be, Ta, LiF and H7Li targets are presented. Nuclear reactions (γ, n) and (p, n) were used to detect MeV photons and protons. The number of MeV photons and protons generated in laser plasmas was found from the measured neutron yield. Possibilities of particle acceleration due to the formation of pinch structures in laser plasmas are discussed. Calculated and experimental results are compared.

Uncommon Regioselectivity in the Thiacalix[4]arene Series: Gross Formylation of the Cone Conformer

Thiacalix[4]arene immobilized in the cone conformation undergoes a direct Gross formylation reaction (Cl(2)CH-O-CH(3)/SnCl(4)/CH(2)Cl(2)) to give the upper-rim formylated thiacalixarene. Albeit using excess of the formylation agent and various reaction temperatures, only one formyl group is introduced into the meta position of the thiacalixarene skeleton. The surprising regioselectivity indicates dramatically different reactivity of the thiacalix[4]arene system when compared with a classical calix[4]arene analogue, which yields exclusively para isomers. The introduction of functional groups into the meta position represents an exceptional substitution pattern in thiacalixarene chemistry, which imparts an interesting conformational behavior to these compounds. The systematic NMR study revealed that the pinched cone-pinched cone equilibrium is remarkably shifted toward one pinched cone structure depending on the substitution.

Low pressure migmatites from the Sanandaj-Sirjan Metamorphic Belt in the Hamedan region (Iran)

Low pressure migmatites from the Sanandaj-Sirjan Metamorphic Belt in the Hamedan region (Iran)Migmatites with evidence for low pressure metamorphism and partial melting occur adjacent to the Alvand Plutonic Complex in the Hamedan region of Iran. They show stromatic, schollen, diktyonitic and massive structure. Sillimanite/andalusite/(kyanite)-garnet- and cordierite-K-feldspar-andalusite-spinel-bearing migmatites are the most common rock types. Some of the granitic intrusions contain xenocrysts which resemble the porphyroblasts of nearby migmatites (e.g. sillimanite, andalusite, cordierite and garnet). Although migmatitic rocks of the region are located near the granitic intrusions, the degree of partial melting is not related to intrusions and is irregular. It appears that partial melting and migmatization pre-date the intrusion of major granitic bodies in the region. Leucosomes in stromatic migmatites are commonly parallel to bedding planes and are mostly formed by metamorphic segregation and/orin situpartial melting (showing mafic selvedges, pinch and swell structures). The melt fraction and migmatite type depend on the chemical composition of parent rocks and the distribution of high strain zones. The formation of thin leucosomes in the stromatic migmatites was controlled by short-range melt movement along the grain boundaries. Melt-rich layers are constrained by pre-existing compositional layering and foliation. Peak metamorphic conditions of ~650 °C and ~300 MPa are consistent with the observed mineral assemblages and the presence of melt in the investigated migmatites.

Generation of MeV photons and protons in laser picosecond plasmas

The results of experiments devoted to studying the generation of MeV photons and protons in picosecond laser plasmas at a laser beam intensity of 1018 W/cm2 on Be, Ta, LiF and H7Li targets are presented. Nuclear reactions (γ, n) and (p, n) were used to detect MeV photons and protons. The number of MeV photons and protons generated in laser plasmas was found from the measured neutron yield. Possibilities of particle acceleration due to the formation of pinch structures in laser plasmas are discussed. Calculated and experimental results are compared.