Twin Cores Research Articles

Formation of contact and multiple cyclic cassiterite twins in SnO2-based ceramics co-doped with cobalt and niobium oxides.

Contact and multiple cyclic twins of cassiterite commonly form in SnO2-based ceramics when SnO2 is sintered with small additions of cobalt and niobium oxides (dual doping). In this work, it is shown that the formation of twins is a two-stage process that starts with epitaxial growth of SnO2 on CoNb2O6 and Co4Nb2O9 seeds (twin nucleation stage) and continues with the fast growth of (101) twin contacts (twin growth stage). Both secondary phases form below the temperature of enhanced densification and SnO2 grain growth; CoNb2O6 forms at ∼700°C and Co4Nb2O9 at ∼900°C. They are structurally related to the rutile-type cassiterite and can thus trigger oriented (epitaxial) growth (local recrystallization) of SnO2 domains in different orientations on a single seed particle. While oriented growth of cassiterite on columbite-type CoNb2O6 grains can only result in the formation of contact twins, the Co4Nb2O9 grains with a structure comparable with that of corundum represent suitable sites for the nucleation of contact and multiple cyclic twins with coplanar or alternating morphology. The twin nucleation stage is followed by fast densification accompanied by significant SnO2 grain growth above 1300°C. The twin nuclei coarsen to large twinned grains as a result of the preferential and fast growth of the low-energy (101) twin contacts. The solid-state diffusion processes during densification and SnO2 grain growth are controlled by the formation of point defects and result in the dissolution of the twin nuclei and the incorporation of Nb5+ and Co2+ ions into the SnO2 matrix in the form of a solid solution. In this process, the twin nuclei are erased and their role in the formation of twins is shown only by irregular segregation of Co and Nb to the twin boundaries and inside the cassiterite grains, and Co,Nb-enrichment in the cyclic twin cores.

Spatio-Temporal Distribution of Tourism Flows and Network Analysis of Traditional Villages in Western Hunan

Traditional village tourism is an effective path to rural revitalization and an excellent way to preserve traditional sceneries and cultural heritage. However, research on the subject matter has been limited. To address some of the current research gaps, this study used 2372 online travelogues from popular travel websites to explore the spatio-temporal distribution and network structure of the tourism flow in traditional villages in western Hunan using ArcGIS and social network analysis. The main findings are as follows: (1) In terms of time distribution, the tourism flow in traditional villages in Western Hunan is dominated by short-term tourism and shows significant seasonal differences. (2) The spatial distribution forms a double-core and multipoint spatial pattern with “Fenghuang Ancient City—Zhangjiajie National Forest Park” as core. (3) The network of traditional villages in Western Hunan exhibits a “core-periphery” hierarchical structure, with a network density of 0.275. Aside from the attraction and appeal of the twin cores, Furong Town and Tianmen Mountain constitute the core points of the network structure, and the radiation drive of the core nodes is not pronounced.

High-Performance Bending Vector and Strain Sensor Using a Dual-Tapered Photonic Crystal Fiber Mach–Zehnder Interferometer

An in-line Mach–Zehnder interferometer based on a dual-tapered photonic crystal fiber (PCF) for bending vector and strain sensing is proposed and experimentally demonstrated. This sensor consists of a 25.7-cm homemade asymmetric twin-core PCF sandwiched between two tapers. Due to the asymmetry of twin cores, two opposite bending directions can be distinguished with the maximum bending sensitivities of 18.29 and −18.13 nm/ $\text{m}^{-1}$ , respectively. By applying axial strain to the sensor, the strain sensitivity reaches up to −10.65 pm/ $\mu \varepsilon $ . Because of the excellent linear response, the effect of temperature on strain and bending sensing can be eliminated by using a measurement matrix. The advantages of bending direction recognition, high strain and bending sensitivities, and compact structure make this sensor attractive for structural deformation monitoring.

Titanium-Coated Dual-Core D-Shaped SPR-Based PCF for Hemoglobin Sensing

Two new dual-core D-shaped SPR (surface plasmon resonance) PCFs (photonic crystal fibers) (DCD-S-SPR PCF) with a splitting barrier between the twin cores are proposed for the detection and sensing of the different bio-samples of human blood. Moreover, each proposed model is displaying a promising performance for different optical parameters, such as refractive index (RI), confinement loss (αc) birefringence (Bi), coupling length (Lc), transmittance (Tx), wavelength sensitivity (Sw), amplitude sensitivity (Sa), resolution, and figure of merit (FOM). However, the observation is done by the finite element method (FEM) for the assumed wavelength range from 2.1 to 3 μm and provides the comparison between two DCD-S-SPR PCF models. The performance indicator measurements for model 1 and model 2 corresponding to the wavelength sensitivity, amplitude sensitivity, resolution, transmittance variance, FOM, and detection limit of each proposed DCD-S-SPR PCF are, respectively, as follows: 12,320.10 nm/RIU, − 230 RIU−1, 1.5 × 10−2 RIU, 4342.34 dB/RIU, 190, 0.21; and 18,550 nm/RIU, − 360 RIU−1, 1.0 × 10−1 RIU, 6071.42 dB/RIU, 250, 0.07. Also, the satisfactory results of those parameters of each hemoglobin sensor confirm the better sensing performance, and the hemoglobin sensor proves itself a tough competitor in the field of PCF-based bio-sensing application.

Novel nanocapsules with Co-TiC twin cores and regulable graphitic shells for superior electromagnetic wave absorption.

The synthesis of nanometer materials with unique structures and compositions has proven successful towards the attenuation of electromagnetic (EM) waves. However, it is still a challenge to form special nanostructures by integrating magnetic/dielectric loss materials into one particle due to the difficulties in coupling the heterogeneous components. Herein, we present the synthesis of novel nanocapsules (NCs) with Co–TiC twin cores encapsulated inside graphitic shells using an arc-discharge plasma method. The thickness of the graphitic shell could be controlled by quantitatively tuning the carbon source concentration. The optimal reflection loss (RL) values of the prepared NCs was −66.59 dB at 8.76 GHz with a low thickness of 2.56 mm. The bandwidth of RL ≤ −10 dB was up to 14.4 GHz, which almost covered the entire frequency band, namely, the S to Ku band (3.6 GHz to 18 GHz). This superior EM wave absorption was ascribed to the specific double-core shell nanostructures and effective impedance matching between the magnetic loss and dielectric loss originating from the combination of the magnetic Co and dielectric TiC/C.

Experimental study of the effect of aging on fluid distribution in Middle Bakken cores

Formation wettability is a critical parameter when designing enhanced oil recovery (EOR) for field applications both in conventional and unconventional reservoirs. In this study, we only focused on one unconventional resource—the Bakken. Specifically, we conducted laboratory experiments in five uncleaned Middle Bakken cores with different initial fluid saturations to determine (1) where the fluids reside within the pores, and (2) the effect of aging on wettability change.The experimental protocol included hydrocarbon-saturation of three uncleaned cores with Bakken oil. The cores were aged at 180 °F and 2500 psi pressure for four weeks, and stored in crude oil for 1 year at ambient laboratory conditions (about 12 psi and 66 °F). Synthetic brine was then used to produce oil from the aged cores by spontaneous imbibition in Amott cell. Additional oil was produced from the cores using a high-speed centrifuge.For the remaining two uncleaned cores, synthetic brine was used to saturate them, and brine was replaced with oil using a centrifuge. The cores were stored in crude oil at ambient laboratory conditions for four months; then, oil recovery from the cores was measured in Amott cell. NMR measurements were conducted on the cores after each fluid saturation/de-saturation experiment to determine the effect of aging time and temperature on the core wettability and fluid distribution in the pores. Also, porosity and permeability of cleaned twin cores were measured at several net confining stresses.The experimental results indicated that hydrocarbon-saturated cores become slightly more oil-wet than brine-saturated cores. NMR measurements indicated that brine resides in smaller pores and as a brine film on grains regardless of aging time, and the core fluids re-distributed with time indicating a strong rock-fluid interaction. Finally, the analysis of oil production indicated the preponderance of chemical osmosis over imbibition as the mechanism of oil displacement in formations with high brine salinity.

Experimental and Theoretical Study of Water and Solute Transport in Organic-Rich Carbonate Mudrocks

Summary The objective of this research is to determine the physicochemical processes underlying water and solute transport in organic-rich source rocks. To achieve this goal, a custom-designed experimental apparatus was constructed to conduct flow tests, founded on a high-pressure triaxial assembly. The apparatus is capable of maintaining core samples at reservoir pressure, temperature, and confining stress. We conducted several 120-day low-salinity osmotic tests in low-clay, organic-rich Eagle Ford carbonate-shale samples. Test results showed gradual, slow increase of pressure within the samples. Because this pressure behavior could not be explained properly with classical models, we formulated a mass-transport mathematical model that relies on fundamental chemical osmosis principles driving low-salinity brine into high-salinity core samples. Our mathematical model was articulated to simulate flow into the core as a 3D porous medium rather than transport across a thin, molecule-selective membrane. The model is dependent on the following principles: The low-salinity brine selectively enters the pores by diffusion mass transport, and the pre-existing, ionized dissolved salt molecules within the core are restrained by internal electrostatic forces to counterdiffuse in the direction opposite to that of the low-salinity-brine molecules entering the pore network. Critical model input data, such as permeability, porosity, and rock compressibility, were obtained from flow experiments on twin cores, and the diffusion coefficient was chosen by history matching. The strengths of the numerical simulation include reliance on mass-transport fundamental principles; not requiring the use of an ambiguously defined membrane-efficiency term; and relying on chemical-potential gradient as the driving force for the low-salinity brine to enter the high-salinity core, generating osmotic pressure within the pore network. The latter implies that osmotic pressure is the consequence of water entering the cores, not the cause. Results of this research have provided a more plausible explanation of pore-scale mass transport in organic-rich shales, and provide useful insights for design of effective enhanced-oil-recovery (EOR) processes.

Effect of natural homointerfaces on the magnetic properties of pseudomorphic La0.7Sr0.3MnO3 thin film: Phase separation vs split domain structure

We studied the effect of naturally formed homointerfaces on the magnetic and electric transport behavior of a heavily twinned, 40nm thick, pseudomorphic epitaxial film of La0.7Sr0.3MnO3 deposited by molecular beam epitaxy on ferroelastic LaAlO3(001) substrate. As proved by high resolution X-ray diffraction analysis, the lamellar twin structure of the substrate is imprinted in La0.7Sr0.3MnO3. In spite of the pronounced thermomagnetic irreversibility in the DC low field magnetization, spin-glass-like character, possibly related to the structural complexity, was ruled out, on the base of AC susceptibility results. The magnetic characterization indicates anisotropic ferromagnetism, with a saturation magnetization Ms = 3.2μB/Mn, slightly reduced with respect to the fully polarized value of 3.7μB/Mn. The low field DC magnetization vs temperature is non bulklike, with a two step increase in the field cooled MFC(T) branch and a two peak structure in the zero field cooled MZFC(T) one. Correspondingly, two peaks are present in the resistivity vs temperature ρ(T) curve. With reference to the behavior of epitaxial manganites deposited on bicrystal substrates, results are discussed in terms of a two phase model, in which each couple of adjacent ferromagnetic twin cores, with bulklike TC = 370K, is separated by a twin boundary with lower Curie point TC = 150K, acting as barrier for spin polarized transport. The two phase scenario is compared with the alternative one based on a single ferromagnetic phase with the peculiar ferromagnetic domains structure inherent to twinned manganites films, reported to be split into interconnected and spatially separated regions with in-plane and out-of-plane magnetization, coinciding with twin cores and twin boundaries respectively.

Design, Fabrication, and Sensor Applications of Photonic Crystal Fibers

Photonic crystal fibers (PCFs) with regularly placed air holes running along the fiber oer flexible design and unique transmission characteristics, like unlimited single-mode operation, that are hard to obtain in conventional optical fibers. In this paper, we will discuss the design, fabrication and sensor applications of photonic crystal fibers, particularly twin-core photonic crystal fibers (TCPCFs) and highly birefringent photonic crystal fibers (HB-PCFs). A numerical analysis of PCFs with various design was performed using a computer code developed with finite element method (FEM). Fabrication of PCFs is mainly based on the well-known stack-and-draw method. Controlled gas pressurization was employed during the fiber drawing process, and the microstructure of PCFs was well preserved by pressurizing the core and cladding regions independently. We will also describe the sensor applications of the fabricated PCFs for measuring the strain, bending, and transverse loads, e.g., TC-PCF-based in-line interferometers and HB-PCF-based birefringent interferometers. In the case of a TC-PCF-based in-line sensor, the small dierence in the eective indices of the two core modes leads to interference fringes, and the birefringence due to the twin cores results in polarization-dependent fringe spacing. A novel intensity-based bend sensor is demonstrated utilizing the bend-induced spatial fringe shift. With a HB-PCF inserted between two linear polarizers, the resulting interference pattern can be used to obtain the transverse load sensitivity for dierent angles of the applied load.

Twin core photonic crystal fiber for in-line Mach-Zehnder interferometric sensing applications

We will discuss fabrication of twin core photonic crystal fiber (TC-PCF) using the stack-and-draw method and its application for in-line Mach-Zehnder interferometers. The small difference in the effective indexes of the two core modes leads to interference fringes and the birefringence of the twin cores results in polarization-dependent fringe spacing. The strain sensitivity was negative and wavelength-dependent. A novel intensity-based bend sensor is also demonstrated with bend-induced spatial fringe shift. High air filling fraction of fabricated TC-PCF cladding provides immunity to bend-induced intensity fluctuation.

Pure ferromagnetism vs. re-entrant spin glass behaviour in epitaxial La0.7Sr0.3MnO3on SrTiO3(001) and LaAlO3(001): the role of the substrate structural transition

Thin films of La0.7Sr0.3MnO3 were grown by molecular beam epitaxy on ferroelastic SrTiO3(001) and LaAlO3(001) substrates, with ferroelastic transition at 105 K and 813 K respectively. High resolution X-ray diffraction analysis proves the presence of twins at room temperature in the films grown onto LaAlO3, while films on SrTiO3 are untwinned. Low field dc magnetization measurements of films onto LaAlO3 are discussed in terms of coexisting ferromagnetic and spin disordered regions, connected to twin cores and twin boundaries respectively; the freezing temperature of the spin glass subsystem scales as H2/3 in the de Almeida–Thouless relation. Spin-glass-like features are absent in films on SrTiO3, in which the ferroelastic transition of the substrate is only marked by a small bump in the low field dc magnetization. The different magnetic behaviour depends on being the ferroelastic transition above or below the film Curie point. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Is it possible to use "twin cores" as a unique sedimentary record? An experimental design based on sediment color

Sedimentary cores are widely used for studying Quaternary records. However, the amount of sediment that is available is proportional to the diameter of the core, which is rarely bigger than 15 cm. One way to obtain more sediment is to use two cores retrieved from almost the same location and use them as if they represent a unique sedimentary record. In the present work, an experimental design has been applied to verify if "twin cores" from an estuary can be considered as representing the same sedimentary record with twice the amount of sediment to study. Because sediment can be characterized based on its color, the variables used as replicates in the experimental design are the three Lab CIE colors acquired with a X-Rite Colortron spectrophotometer. Sediment cores were retrieved from the upper saltmarsh of Gilão River's estuary, southern Portugal. Twin cores, with in between distances of 50 cm, 100 cm and 200 cm, from two different sites were analysed. Results from a nested ANOVA show that even for the closest twin cores (50 cm apart) there is at least one color variable that shows significant variations between the profiles of both cores. These results clearly show that "twin cores" cannot be used as a unique sedimentary record without any previous testing, at least in such transitional regions.

ATCA 3 mm observations of NGC 6334I and I(N): dense cores, outflows, and an UCH II region

Aims. We investigate the dense gas, the outflows, and the continuum emission from the massive twin cores NGC 6334I and I(N) at high spatial resolution. Methods. We imaged the region with the Australia Telescope Compact Array (ATCA) at 3.4 mm wavelength in continuum, as well as CH3CN(5K −4K ) and HCN(1−0) spectral line emission. Results. While the continuum emission in NGC 6334I mainly traces the UCHii region, toward NGC 6334I(N) we detect continuum emission from four of the previously identified dust continuum condensations that are of protostellar or pre-stellar nature. The CH3CN(5K −4K ) lines are detected in all K-components up to energies of 128 K aboveground toward two protostellar condensations in both regions. We find line width increasing with increasing K for all sources, which indicates a higher degree of internal motions of the hotter gas probed by these high K-transitions. Toward the main mm and CH3CN source in NGC 6334I, we identify a velocity gradient approximately perpendicular to the large-scale molecular outflow. This may be interpreted as a signature of an accretion disk, although other scenarios, e.g., an unresolved double source, could produce a similar signature. No comparable signature is found toward any of the other sources. HCN does not trace the dense gas well in this region but it is dominated by the molecular outflows. While the outflow in NGC 6334I exhibits a normal Hubble-law like velocity structure, the data are consistent with a precessing outflow close to the plane of the sky for NGC 6334I(N). Furthermore, we observe a wide (∼15.4 km s −1 ) HCN absorption line, much broader than the previously observed CH3OH and NH3 absorption lines. Several explanations for the difference are discussed. The fits-files of the 3.4 mm continuum images and of the HCN(1−0) and CH3CN(5K−4K ) data-cubes are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat? J/481/169

High-altitude varve records of abrupt environmental changes and mining activity over the last 4000 years in the Western French Alps (Lake Bramant, Grandes Rousses Massif)

Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial Lake Bramant (Grandes Rousses Massif, French Alps), under and overlying a large slump identified by high-resolution seismic profile, allow the investigation of Holocene natural hazards and interactions between human activity and climatic changes at high-altitude. Annual sedimentation throughout the cores (glacial varves) is identified on photographs, ITRAX (high-resolution continuous microfluorescence-X) and CAT-Scan (computerized axial tomography) analyses and is supported by (1) the number of dark and light laminations between dates obtained by radionuclide measurements ( 137Cs, 241Am), (2) the correlation of a slump triggered by the nearby AD 1881 Allemond earthquake (MSK intensity VII) and of a turbidite triggered by the AD 1822 Chautagne regional earthquake (MSK intensity VIII), (3) the number of laminations between two accelerator mass spectrometry (AMS) 14C dates, and (4) archaeological data. In Lake Bramant, dark layers are coarser, contain less detrital elements, but more neoformed elements and organic matter content. These darker laminations result from calm background sedimentation, whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt. Traces of mining activity during the Roman civilization apogee (AD 115–330) and during the Early Bronze Age (3770–3870 cal BP) are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the NW Alps. Warmer climate during the Bronze Age in this part of the Alps is suggested by (1) two organic deposits (4160–3600 cal BP and 3300–2850 cal BP) likely reflecting a lower lake level and smaller glaciers and (2) evidence of a different vegetation cover around 2500 m a.s.l. The onset of clastic proglacial sedimentation between 3600–3300 cal BP and since 2850 cal BP is synchronous with periods of glacier advances documented in the Alps and high-lake levels in west-central Europe. This major change in proglacial sedimentation highlights the development of a larger St. Sorlin glacier in the catchment area of Lake Bramant.

Hot ammonia in NGC 6334I & I(N)

Aims. The massive twin cores NGC 6334I and I(N) are in different evolutionary stages and hence ideal targets to study evolutionary variations within the same larger-scale environment. Here, we study the warm, compact gas components. Methods. We imaged the two regions with the Australia Telescope Compact Array (ATCA) at high angular resolution in the NH3(3, 3) to (6, 6) inversion lines. Results. Compact emission is detected toward both regions in all observed inversion lines with energy levels up to 407 K above ground. This is particularly surprising for NGC 6334I(N) since it lacks bright infrared emission and is considered a massive cold core at an early evolutionary stage. High optical depth and multiply-peaked line profiles complicate rotation temperature estimates, and we can only conclude that gas components with temperatures >100K are present in both regions. Toward NGC 6334I, we confirm previous reports of NH3(3, 3) maser emission toward the outflow bow-shocks. Furthermore, we report the first detection of an NH3(6, 6) maser toward the central region of NGC 6334I. This maser is centered on the second millimeter (mm) peak and elongated along the outflow axis, indicating that this mm continuum core harbors the driving source of the molecular outflow. Toward the main mm peak in NGC 6334I(N), we detect a double-horn line profile in the NH3(6, 6) transition. The current data do not allow us to differentiate whether this double-horn profile is produced by multiple gas components along the line of sight, or whether it may trace a potential underlying massive accretion disk.

Visualization of elastic strain fields by the spatial distribution of the blue luminescence in a twinned microcline crystal

This paper correlates the mineralogical characteristics of twinning and exsolutions of a microcline giant crystal with macroscopic twin-domains and perthitic texture, taken from the Golconda III granitic pegmatite (Minas Gerais, Brazil), with the spatial distribution of the blue luminescence from radiation-induced O− defects. The twinning macrostructure and the Na distribution of the microcline have been studied by optical microscopy, backscattered electron scanning electron microscopy (SEM), chemical mapping and quantitative chemical analyses with electron microprobe. Spectra luminescence data were recorded by high sensitivity thermoluminescence, X-ray radioluminescence, cathodoluminescence (CL) and also CL-imaging under optical microscope at room temperature, and under SEM at liquid nitrogen temperature. The crystal recorded three different stages of re-equilibration during the geological cooling: (1) building up of regular macrostructures, formed mainly by only two Albite-twin law orientation variants, by solid-state domain self-assembly; (2) coarsening of one orientation variant at the expenses of the other by dissolution–reprecipitation reactions and (3) later degradation of regular twins into irregular domains. The spatial distribution of the blue luminescence in microcline can be used for two practical applications: (1) to mark water-rich fluid-flow channelways at low temperatures in which these light emissions are absent and (2) to visualize elastic strain fields across twin patterns, with maxima emission from the Na-rich (0 1 0) boundaries and remnants Pericline twin cores and minima from the Na-poor (0 1 0) twin cores and residual Pericline boundaries. Elastic strain must be the physical factor determining the radiation sensitivity of the lattice, i.e. radiation damage is not random in twinned lattices and defect formation occurs preferentially at the sites with high local elastic strain. Environmental ionizing radiation could involve a twofold effect during subsolidus microcline re-equilibration, i.e. Si/Al re-ordering, mainly acting on coherent twin boundaries, and also producing reactive \({\rm H}\raise0.145em\hbox{${\scriptscriptstyle \bullet}$} \) and \({\rm OH}\raise0.145em\hbox{${\scriptscriptstyle \bullet}$} \) radicals as radiolytic products of water.

High Spatial Resolution Observations of NH3and CH3OH toward the Massive Twin Cores NGC 6334I and NGC 6334I(N)

Molecular line observations of NH3 (J ; K) ¼ (1; 1) and (2, 2) and CH3OH at 24.93 GHz taken with the Australian Telescope Compact Array (ATCA) toward the massive twin cores NGC 6334I and NGC 6334I(N) reveal significant variations in the line emission between the two massive cores. The UC H ii region/hot core NGC 6334I exhibits strong thermal NH3 and CH3OH emission adjacent to the UC H ii region and coincident with two millimeter continuum peaks observed by T. R. Hunter et al. In contrast, we find neither compact NH3 nor thermal CH3OH line emission toward NGC 6334I(N). There the NH3 emission is distributed over a broad region (>10) without a clear peak, and we find Class I CH3OH maser emission with peak brightness temperatures up to 7000 K. The maser emission peaks appear to be spatially associated with the interfaces between the molecular outflows and the ambient dense gas. Peak NH3 (1, 1) line brightness temperatures 70 K in both regions indicate gas temperatures on the same order. NH3 emission is also detected toward the outflow in NGC 6334I, resulting in an estimated rotational temperature of Trot 19 K. Furthermore, we observe CH3OH and NH3 absorption toward the UC H ii region; the velocity structure is consistent with expanding molecular gas around the UC H ii region. Thermal and kinematic effects possibly imposed from the UC H ii region on the molecular core are also discussed.

Condition Assessment of a Deteriorated Cement Works

This paper describes the condition assessment of a 30 year old cement works, where some of the structures were clearly deteriorated. It was carried out for the purpose of obtaining material properties needed for evaluating strength and integrity, and for establishing durability. This was done by sampling the structures using the nondestructive techniques of visual inspection, perusal of drawings, ultrasonic pulse velocity measurements, covermeter surveys, and core testing. Core testing gave information not only about strength but also about sorptivity, carbonation, chlorides, and sulfates, and about the variation of some of these properties with depth from the concrete surface. Some new approaches were used to estimate the grade of concrete and the partial safety factor for reinforcement. The use of “twin cores” (surface and internal) indicated that the surface quality of the concrete was actually better than the internal quality. Recommendations for repair and maintenance dealt with (1) accumulated cemen...

Variable demultiplexing using a twin-core fiber Mach-Zehnder interferometer

A novel form of demultiplexer is demonstrated using a single untapered length of twin-core fiber. The degree of demultiplexing can be varied so that an arbitrary amount of power at a given wavelength (e.g., 1.3 mu m) can be removed from a multiplex to two wavelengths (e.g., 1.3/1.55 mu m). The variation is achieved by locally bending the fiber in the plane of the twin cores. Channel spacings of 30 nm have been achieved experimentally.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Grating-assisted couplers

A simple closed-form description of grating-assisted coupling between twin cores is presented. It is exact in the limit of weakly coupled cores and weak grating perturbations.