Isotropic Region Research Articles

Energy and water vapor transport across a simplified cloud-clear air interface

We consider a simplified physics of the could interface where condensation, evaporation and radiation are neglected and momentum, thermal energy and water vapor transport is represented in terms of the Boussinesq model coupled to a passive scalar transport equation for the vapor. The interface is modeled as a layer separating two isotropic turbulent regions with different kinetic energy and vapor concentration. In particular, we focus on the small scale part of the inertial range of the atmospheric boundary layer as well as on the dissipative range of scales which are important to the micro-physics of warm clouds. We have numerically investigated stably stratified interfaces by locally perturbing at an initial instant the standard temperature lapse rate at the cloud interface and then observing the temporal evolution of the system. When the buoyancy term becomes of the same order of the inertial one, we observe a spatial redistribution of the kinetic energy which produce a concomitant pit of kinetic energy within the mixing layer. In this situation, the mixing layer contains two interfacial regions with opposite kinetic energy gradient, which in turn produces two intermittent sublayers in the velocity fluctuations field. This changes the structure of the field with respect to the corresponding non-stratified shearless mixing: the communication between the two turbulent region is weak, and the growth of the mixing layer stops. These results are discussed with respect to Large Eddy Simulations data for the Planetary Boundary Layers.

Physicochemical behaviors of cationic gemini surfactant (14-4-14) based microheterogeneous assemblies.

A comprehensive study of micellization and microemulsion formation of a cationic gemini surfactant (tetramethylene-1,4-bis(dimethyltetradecylammonium bromide; 14-4-14) in the absence or presence of hydrophobically modified polyelectrolyte, sodium carboxymethylcellulose (NaCMC), has been conducted by conductometry, tensiometry, microcalorimetry, and fluorimetry methods at different temperatures. Both critical micelle concentration and degree of ionization of the surfactant have been observed to increase with increasing temperature. The interfacial and thermodynamic parameters were evaluated. The standard Gibbs free energy of micellization (ΔGm°) is negative, which decreases with increase in temperature. Larger entropic contribution is observed compared to the enthalpy. The interaction of 14-4-14 with NaCMC produces coacervates which was determined from turbidimetry method. The pseudoternary phase behavior of the microemulsion systems comprising water (or NaCMC as additive), 14-4-14, isopropanol (IP) or n-butanol (Bu) as cosurfactant, and isopropyl myristate (IPM) were studied at 298 K. Phase diagrams reveal that IP derived microemulsions (in the absence of NaCMC) offer a large isotropic region compared to Bu-derived systems at comparable physicochemical conditions. Increasing the concentration of IP or Bu decreases the isotropic region in the phase diagram. NaCMC influences the microemulsion zone, depending upon its concentration, and type of cosurfactant and surfantant/cosurfactant ratio. Dynamic light scattering and conductometric measurements show the size of the droplet, threshold temperature of percolation, scaling parameters, and activation energy of the percolation process of 14-4-14/IP or Bu derived microemulsion systems without/with NaCMC at various physicochemical conditions. Bu exerts a greater effect to reduce θt than IP as a cosurfactant (in the absence of NaCMC) at comparable ω. On the other hand, IP showed better percolating effect than Bu in the presence of NaCMC. Bu and IP (as cosurfactant) and NaCMC (as additive) influenced the microemulsion droplet size (Dh) to different extents under comparable conditions. Temperature insensitive microemulsions have been reported at the studied temperature range (298–353 K). 14-4-14/IP (1:2)-derived microemulsion showed a fractured surface at fixed ω = 15, where ω is the water and surfactant molar ratio, and temperature (298 K); whereas, large scale mesospheres comprising multiple closely winded nanoslices and spheroid morphology were formed in 14-4-14/IP and 14-4-14/Bu microemulsions, respectively, in the presence of 0.01 g % NaCMC, at comparable conditions. These systems revealed good antimicrobial activity toward the strains of Gram-positive Bacillus subtilis and Gram-negative Escherichia coli bacteria at 298 K, and inhibitory effect was governed by ω, type of cosurfactant, and bacterial strains.

Self-Assembly of Didodecyldimethylammonium Surfactants Modulated by Multivalent, Hydrolyzable Counterions

The self-assembly behavior of double-chained didodecyldimethylammonium (DDA(+)) surfactants with hydrolyzable phosphate (PO4(3-), HPO4(2-), and H2PO4(-)), oxalate (HC2O4(-) and C2O4(2-)), and carbonate (HCO3(-)/CO3(2-)) counterions was found to depend on both the counterion and its hydrolysis state, as determined by the pH of the system. Carbonate and phosphate ions at all hydrolysis states successfully stabilize an extended isotropic micellar solution region. These micelles are well-described as prolate ellipsoids which vary in size and aspect ratio depending on the surfactant concentration and hydrolysis state of the counterion. Both oxalate counterions form bilayer structures in dilute solution. The structures found with divalent oxalate, C2O4(2-), ions possessed very limited swelling capacity compared to the bilayer structures formed with monovalent oxalate, HC2O4(-), ions. The lamellar (Lα) phase was universally formed at sufficiently high surfactant concentrations for all hydrolyzable counterions. Two intermediate structures corresponding to a disordered mesh (Lα(D)) and tetragonal ordered mesh (T) phase were found to form with DDA2HPO4 prior to the Lα phase but not with other phosphate counterions.

Non-Negative Spherical Deconvolution (NNSD) for estimation of fiber Orientation Distribution Function in single-/multi-shell diffusion MRI

Spherical Deconvolution (SD) is commonly used for estimating fiber Orientation Distribution Functions (fODFs) from diffusion-weighted signals. Existing SD methods can be classified into two categories: 1) Continuous Representation based SD (CR-SD), where typically Spherical Harmonic (SH) representation is used for convenient analytical solutions, and 2) Discrete Representation based SD (DR-SD), where the signal profile is represented by a discrete set of basis functions uniformly oriented on the unit sphere. A feasible fODF should be non-negative and should integrate to unity throughout the unit sphere S2. However, to our knowledge, most existing SH-based SD methods enforce non-negativity only on discretized points and not the whole continuum of S2. Maximum Entropy SD (MESD) and Cartesian Tensor Fiber Orientation Distributions (CT-FOD) are the only SD methods that ensure non-negativity throughout the unit sphere. They are however computational intensive and are susceptible to errors caused by numerical spherical integration. Existing SD methods are also known to overestimate the number of fiber directions, especially in regions with low anisotropy. DR-SD introduces additional error in peak detection owing to the angular discretization of the unit sphere. This paper proposes a SD framework, called Non-Negative SD (NNSD), to overcome all the limitations above. NNSD is significantly less susceptible to the false-positive peaks, uses SH representation for efficient analytical spherical deconvolution, and allows accurate peak detection throughout the whole unit sphere. We further show that NNSD and most existing SD methods can be extended to work on multi-shell data by introducing a three-dimensional fiber response function. We evaluated NNSD in comparison with Constrained SD (CSD), a quadratic programming variant of CSD, MESD, and an L1-norm regularized non-negative least-squares DR-SD. Experiments on synthetic and real single-/multi-shell data indicate that NNSD improves estimation performance in terms of mean difference of angles, peak detection consistency, and anisotropy contrast between isotropic and anisotropic regions.

Design of Plasmonic Perfect Absorbers for Quantum-well Infrared Photodetection

Based on analytic formulas and numerical simu- lations, we propose a plasmonic cavity with a top Au grating and bottom Au film to enhance quantum-well infrared pho- todetectors (QWIPs) operating at wavelengths between 2 and 30 μm. By using plasmonic cavity modes, QWIPs can detect light even at normal incidence. With using optimal structural parameters, light can be almost perfectly absorbed by the cavity and over 54 % of the light is absorbed by the QW active region. Compared with the reference structure (without Au layers and with an isotropic active region), the absorption enhancement is over 30 times in the QW active region at normal incidence and remains high value (> 4.5) for p -polarized light in a broad range of incident angle (|θ| < 60 0 ).

Tween-80–n-Butanol–Diesel–Water Microemulsion System—A Class of Alternative Diesel Fuel

Tween-80–n–butanol–diesel–water microemulsion systems with various surfactant:cosurfactant (S:C) ratio have been reported as a class of alternative diesel fuel from their phase behavior, clouding phenomena, conductivity, turbidity, and inflammation studies. Temperature induced clouding of microemulsion containing 2% brine at an S:C ratio of 1:1 from a suitable turbid zone has been examined to see the stability of the diesel–water microemulsion systems. Regression models have been proposed to understand the impact of various components of the microemulsion on their cloud point (CP) values. Conductivity of the microemulsions at various S:C ratio increases with the volume of brine having two cut points depicting the presence of three microheterogenous phases within the system, whereas turbidity shows a linear increase. Dye-probed investigation of water-rich and oil-rich zones of the microemulsions indicates the involvement of a dynamic mass transfer process within the various zones. The intensities of flames produced during burning of the microemulsions with various O:E:W weight percentages selected from the isotropic regions of the phase diagrams have been estimated using MATLAB image processing method and the impacts of various components on the fuel use of the microemulsions have been analyzed.

Long-range electronic reconstruction to a dxz,yz-dominated Fermi surface below the LaAlO₃/SrTiO₃ interface.

Low dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions - i.e. the interfacial “depth” - remains unclear. Examining LaAlO3/SrTiO3 heterostructures at previously unexplored carrier densities n2D ≥ 6.9 × 1014 cm−2, we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferential dxz,yz orbital occupancy extending over at least 100 nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO3 emerge simultaneously at higher n2D. We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.

Sign choice for the index of refraction for arbitrary complex values of permittivity and permeability: Formal analysis

It is shown that for an isotropic homogenous material region the expression for characteristic impedance Z=μc/n is more general than the usual expression Z=μ/ε. This alternative expression together with the condition Re(Z) ≥ 0 uniquely determines the sign of the index of refraction n=±cμε for all values of ε and μ. Thus, the celebrated Veselago's argument that n &amp;lt; 0 for real negative values of ε and μ is rigorously generalized. A discussion of physically realizable complex material parameters ensues by considering the prescribed sign choice of n together with energy conservation.

Anisotropic conductivity tensor imaging in MREIT using directional diffusion rate of water molecules

Magnetic resonance electrical impedance tomography (MREIT) is an emerging method to visualize electrical conductivity and/or current density images at low frequencies (below 1 KHz). Injecting currents into an imaging object, one component of the induced magnetic flux density is acquired using an MRI scanner for isotropic conductivity image reconstructions. Diffusion tensor MRI (DT-MRI) measures the intrinsic three-dimensional diffusion property of water molecules within a tissue. It characterizes the anisotropic water transport by the effective diffusion tensor. Combining the DT-MRI and MREIT techniques, we propose a novel direct method for absolute conductivity tensor image reconstructions based on a linear relationship between the water diffusion tensor and the electrical conductivity tensor. We first recover the projected current density, which is the best approximation of the internal current density one can obtain from the measured single component of the induced magnetic flux density. This enables us to estimate a scale factor between the diffusion tensor and the conductivity tensor. Combining these values at all pixels with the acquired diffusion tensor map, we can quantitatively recover the anisotropic conductivity tensor map. From numerical simulations and experimental verifications using a biological tissue phantom, we found that the new method overcomes the limitations of each method and successfully reconstructs both the direction and magnitude of the conductivity tensor for both the anisotropic and isotropic regions.

Antioxidant SkQ1 delays sarcopenia-associated damage of mitochondrial ultrastructure

A comparative electron-microscopic study of ultrastructure of mitochondria in skeletal muscles of the 3- and 24-month-old Wistar and OXYS rats revealed age-dependent changes in both general organization of the mitochondrial reticulum and ultrastructure of mitochondria. The most pronounced ultrastructure changes were detected in the OXYS rats suffering from permanent oxidative stress. In the OXYS rats, significant changes in mitochondrial ultrastructure were detected already at the age of 3 months. Among them, there were the appearance of megamitochondria and reduction of cristae resulting in formation of cristae-free regions inside mitochondria. In the 24-month-old OXYS rats, mitochondrial reticulum was completely destroyed. In the isotropic region of muscle fiber, only small solitary mitochondria were present. There appeared regions of lysed myofibrils as well as vast regions filled with autophagosomes. A mitochondrial antioxidant SkQ1 (given to rats with food daily in the dose of 250 nmol/kg of body weight for 5 months beginning from the age of 19 months) prevented development of age-dependent destructive changes in both the Wistar and OXYS rats.

Highly cross-linked polyethylene in total hip and knee replacement: spatial distribution of molecular orientation and shape recovery behavior.

The present study investigated effects of processing procedures on morphology of highly cross-linked and re-melted UHMWPE (XLPE) in total hip and knee arthroplasty (THA, TKA). The shape recovery behavior was also monitored via uniaxial compression test at room temperature after non-destructive characterizations of the in-depth microstructure by confocal/polarized Raman spectroscopy. The goal of this study was to relate the manufacturing-induced morphology to the in vivo micromechanical performance, and ultimately to explore an optimal structure in each alternative joint bearing. It was clearly confirmed that the investigated XLPE hip and knee implants, which were produced from different orthopaedic grade resins (GUR 1050 and GUR 1020), consisted of two structural regions in the as-received states: the near-surface transitional anisotropic layer (≈100 μm thickness) and the bulk isotropic structural region. These XLPEs exhibited a different crystalline anisotropy and molecular texture within the near-surface layers. In addition, the knee insert showed a slightly higher efficiency of shape recovery against the applied strain over the hip liner owing to a markedly higher percentage of the bulk amorphous phase with intermolecular cross-linking. The quantitative data presented in this study might contribute to construct manufacturing strategies for further rationalized structures as alternative bearings in THA and TKA.

Homogeneity and isotropy in a laboratory turbulent flow

We present a new design for a stirred tank that is forced by two parallel planar arrays of randomly actuated synthetic jets. This arrangement creates turbulence at high Reynolds number with low mean flow. Most importantly, it exhibits a region of 3D homogeneous isotropic turbulence that is significantly larger than the integral lengthscale. These features are essential for enabling laboratory measurements of turbulent suspensions. We use quantitative imaging to confirm isotropy at large, small, and intermediate scales by examining one-- and two--point statistics at the tank center. We then repeat these same measurements to confirm that the values measured at the tank center are constant over a large homogeneous region. In the direction normal to the symmetry plane, our measurements demonstrate that the homogeneous region extends for at least twice the integral length scale $L=9.5$ cm. In the directions parallel to the symmetry plane, the region is at least four times the integral lengthscale, and the extent in this direction is limited only by the size of the tank. Within the homogeneous isotropic region, we measure a turbulent kinetic energy of $6.07 \times 10^{-4} $m$^2$s$^{-2}$, a dissipation rate of $4.65 \times 10^{-5} $m$^2$s$^{-3}$, and a Taylor--scale Reynolds number of $R_\lambda=334$. The tank's large homogeneous region, combined with its high Reynolds number and its very low mean flow, provides the best approximation of homogeneous isotropic turbulence realized in a laboratory flow to date. These characteristics make the stirred tank an optimal facility for studying the fundamental dynamics of turbulence and turbulent suspensions.

Highly conductive, completely amorphous polymer electrolyte membranes fabricated through photo-polymerization of poly(ethylene glycol diacrylate) in mixtures of solid plasticizer and lithium salt

Abstract Ternary phase diagram of prepolymer mixtures containing poly(ethylene glycol diacrylate) (PEGDA), succinonitrile (SCN) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) has been established in order to provide guidance for producing completely amorphous self-standing solid electrolyte membranes. The phase diagram of the precursor mixtures, thus obtained, consisted of a wide isotropic amorphous region, crystal + amorphous coexistence region at high lithium salt concentrations and plastic crystal + amorphous coexistence region at succinonitrile-rich compositions. Of particular interest is that upon photo-polymerization of isotropic compositions, the resulting networks remained completely amorphous without undergoing polymerization-induced phase separation or polymerization-induced crystallization. The ionic conductivity was mapped out as a function of composition within the isotropic region of the starting ternary phase diagram in conjunction with room temperature conductivities showing high ionic conductivities on the order of 10 − 3 S cm − 1 at several compositions. These solid state polymer electrolyte membranes are transparent, light weight, and flexible, which can be shaped in any forms with space saving attributes. More importantly, no solvent is required in the membrane fabrication as well as in the battery operation, thereby improving safety and cost effectiveness.

Two‐Dimensional Coupled Hydromechanical Modeling of Water Infiltration into a Transversely Isotropic Unsaturated Soil Region

The partial differential governing equation governing fluid infiltration into an unsaturated transversely isotropic porous medium was developed by considering mass conservation, Darcy's law, and the elastic deformability of the porous skeleton. Analytical solutions for two‐dimensional coupled infiltration in an unsaturated porous medium of finite extent were obtained using a Fourier transform technique. The analytical formulation was used to examine the two‐dimensional infiltration and evaporation problem for a transversely isotropic unsaturated porous medium. This study provides a comparison between the analytical solution and computational estimates for a two‐dimensional coupled infiltration problem in a transversely isotropic deformable porous region where there is recharge at the surface. The results indicate that the pressure head changes occur most rapidly when the unsaturated porous medium is hydraulically isotropic.

Design principle of Au grating couplers for quantum-well infrared photodetectors

Based on analytic formulas and numerical simulations, we investigate the enhancement effect of Au gratings with spoof plasmon resonances on quantum-well infrared photodetectors (QWIPs) operating between 2 and 30μm. It is found that a simple analytic formula can well estimate the resonant wavelengths of Au gratings. Using optimal grating parameters, the absorption in the QW active region can be enhanced by 4-5 times compared with that in the reference structure (without gratings and with an isotropic active region). For s-polarized light, a high enhancement (>1.4) can occur in a broad range of incident angle (|θ|<40°).

The influence of inorganic salts on the rheological properties of 1,3-propanediyl bis(dodecyl dimethylammonium bromide) and sodium dodecylsulfonate aqueous mixed system

The rheological properties of isotropic 12-3-12/AS/H2O mixed systems in the absence and in the presence of salt have been investigated. The addition of AS into 12-3-12 aqueous solution or vice versa, or the addition of salt into isotropic 12-3-12/AS/H2O mixed systems, leads to changes in microstructure, phase behavior, shear viscosity η, and rheological behavior. In the process of gradually adding AS (or salt) to 12-3-12 aqueous solution, the microstructural transitions are as follows: coexistence of spherical micelles and rodlike micelles→somewhat elongation of rodlike micelles→coexistence of rodlike micelles and vesicles→vesicles; and the rheological behaviors change as follows: antithixotropic and shear thickening→complex thixotropic→shear thinning and thixotropic. η increases initially to a peak, then decreases, and finally the further addition of AS or salt results in aqueous two-phase separation. The origin and the small value (∼510mPas) of the η peak for isotropic 12-3-12/AS/H2O mixed system with excess 12-3-12 are linked with the above microstructural transitions. The η peak becomes lower with the addition of salt. The salt effect on the η peak is related to the matching of water affinities between the counterions and ionic head groups of surfactant. The isotropic 12-3-12/AS/H2O mixed systems with excess AS are Newtonian fluids or near Newtonian fluids with η≈0.75mPas under the shear rate of 1500s−1 due to the coexistence of spherical micelles and short rodlike micelles. The addition of salt changes these Newtonian or near Newtonian fluids to antithixotropic fluids, or complex thixotropic fluids, or thixotropic fluids, and leads to somewhat increase of η (usually less than 25mPas). Two-parameter power-law is used to model the above mentioned fluids. Most of the fluids excepting a few shear thinning fluids located near the phase boundary between isotropic single-phase region and adjacent aqueous two-phase region obey the power-law model.

Non-equilibrium nature of two-dimensional isotropic and nematic coexistence in amyloid fibrils at liquid interfaces

Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic-nematic phase transition. Here we employ single-molecule atomic force microscopy, cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S(2D)(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic-nematic coexistence to non-equilibrium phenomena.

Phase Behavior and Formation of Oleyl Ester Nanoemulsions System

Oleylesters (OEs) are newly synthesized esters from different fatty acids of different chain length and oleyl alcohol using Novozyme 435 as catalyst. The phase behavior of these esters were determined by constructing the pseudoternaryphase diagrams of OEs/Tween 80/water at 25.0 ± 0.5°C. Compositions from the isotropic and homogeneous region were selected for characterization. The shortest OEs chain represents the most stable nanoemusions system with the smallest droplet for both isotropic and homogeneous regions. The results from simulation study showed that the shape of emulsion droplet was in spherical shape with the values of eccentricity (e) 0.11 to 0.17.

CT-scan images preprocessing and segmentation to improve bioprosthesis leaflets morphological analysis

The visualization of bioprosthesis leaflet morphology might help to better understand the underlying mechanism of dysfunction in degenerated aortic bioprosthesis. Because today such visualization of bioprosthesis leaflet morphology is intricate to impossible with other imaging techniques, we hypothesized that the processing of multi-detector CT images would allow better visualization of the prosthetic valve leaflets after biological aortic valve replacement. The purpose of our study was to prospectively evaluate patients with a degenerated aortic bioprosthesis, waiting for reoperation, by using 64-slice CT to evaluate prosthetic leaflets morphology. A semi-automatic segmentation of pre-operative tomodensitometric images was conducted, using 2 different implementations of the region growing algorithm. Here we report all segmentation steps (selection of the region of interest, filtering, segmentation). Studied degenerated aortic bioprostheses were represented by two Carpentier-Edwards Supra Annular Valve (porcine leaflets), one Edwards Perimount (pericardial leaflets) and one Medtronic Mosaic (porcine leaflets). Both segmentation methods (Isotropic Region Growing and Stick Region Growing) allowed a semi-automatic segmentation with 3D reconstruction of all bioprosthetic components (stent, leaflets, degeneration/calcifications). Explanted bioprosthesis CT images were also processed and used as reference. Segmentation results were compared by means of quantitative criteria. Semi-automatic segmentation using region growing algorithm seems to provide an interesting approach for the morphological characterization of degenerated aortic bioprostheses. We believe that in the next future CT scan images segmentation may play an important role to better understand the mechanism of dysfunction in failing aortic bioprostheses. Moreover, bioprostheses 3D reconstructions could be integrated into preoperative planning tools to optimize valve-in-valve procedure.

Ground states of spin-12triangular antiferromagnets in a magnetic field

We use a combination of numerical density matrix renormalization group calculations and several analytical approaches to comprehensively study a simplified model for a spatially anisotropic spin-$\frac{1}{2}$ triangular lattice Heisenberg antiferromagnet: the three-leg triangular spin tube (TST). The model is described by three Heisenberg chains, with exchange constant $J$, coupled antiferromagnetically with exchange constant ${J}^{\ensuremath{'}}$ along the diagonals of the ladder system, with periodic boundary conditions in the shorter direction. Here, we determine the full phase diagram of this model as a function of both spatial anisotropy (between the isotropic and decoupled chain limits) and magnetic field. We find a rich phase diagram, which is remarkably dominated by quantum states: the phase corresponding to the classical ground state appears only in an exceedingly small region. Among the dominant phases generated by quantum effects are commensurate and incommensurate coplanar quasiordered states, which appear in the vicinity of the isotropic region for most fields, and in the high-field region for most anisotropies. The coplanar states, while not classical ground states, can at least be understood semiclassically. Even more strikingly, the largest region of phase space is occupied by a spin density wave phase, which has incommensurate collinear correlations along the field. This phase has no semiclassical analog, and may be ascribed to enhanced one-dimensional fluctuations due to frustration. Cutting across the phase diagram is a magnetization plateau, with a gap to all excitations and ``up-up-down'' spin order, with a quantized magnetization equal to $\frac{1}{3}$ of the saturation value. In the TST, this plateau extends almost but not quite to the decoupled chains limit. Most of the above features are expected to carry over to the two-dimensional system, which we also discuss. At low field, a dimerized phase appears, which is particular to the one-dimensional nature of the TST, and which can be understood from quantum Berry phase arguments.