Unconfined States Research Articles

Diffusion barriers imposed by tissue topology shape Hedgehog morphogen gradients

Animals use a small number of morphogens to pattern tissues, but it is unclear how evolution modulates morphogen signaling range to match tissues of varying sizes. Here, we used single-molecule imaging in reconstituted morphogen gradients and in tissue explants to determine that Hedgehog diffused extracellularly as a monomer, and rapidly transitioned between membrane-confined and -unconfined states. Unexpectedly, the vertebrate-specific protein SCUBE1 expanded Hedgehog gradients by accelerating the transition rates between states without affecting the relative abundance of molecules in each state. This observation could not be explained under existing models of morphogen diffusion. Instead, we developed a topology-limited diffusion model in which cell-cell gaps create diffusion barriers, which morphogens can only overcome by passing through a membrane-unconfined state. Under this model, SCUBE1 promoted Hedgehog secretion and diffusion by allowing it to transiently overcome diffusion barriers. This multiscale understanding of morphogen gradient formation unified prior models and identified knobs that nature can use to tune morphogen gradient sizes across tissues and organisms.

A Fast Tunable 3D-Transmon Architecture for Superconducting Qubit-Based Hybrid Devices

Superconducting qubits utilize the strong non-linearity of the Josephson junctions. Control over the Josephson nonlinearity, either by a current bias or by the magnetic flux, can be a valuable resource that brings tunability in the hybrid system consisting of superconducting qubits. To enable such a control, here we incorporate a fast-flux line for a frequency tunable transmon qubit in 3D cavity architecture. We investigate the flux-dependent dynamic range, relaxation from unconfined states, and the bandwidth of the flux-line. Using time-domain measurements, we probe transmon's relaxation from higher energy levels after populating the cavity with $\approx 2.1\times10^4$ photons. For the device used in the experiment, we find a resurgence time corresponding to the recovery of coherence to be 4.8~$\mu$s. We use a fast-flux line to tune the qubit frequency and demonstrate the swap of a single excitation between cavity and qubit mode. By measuring the deviation in the transferred population from the theoretical prediction, we estimate the bandwidth of the flux line to be $\approx$~100~MHz, limited by the parasitic effect in the design. These results suggest that the approach taken here to implement a fast-flux line in a 3D cavity could be helpful for the hybrid devices based on the superconducting qubit.

Overcoming Limitations in Surface Geometry‐Driven Bubble Transport: Bidirectional and Unrestricted Movement of an Underwater Gas Bubble Using a Magnetocontrollable Nonwetting Surface

AbstractThe movement of underwater gas bubbles significantly affects the core processes of a variety of applications in water electrolysis, heat transfer, optofluidics, and other fields. To maneuver the motion of bubbles, surface geometry‐driven transport is widely applied by employing asymmetric nonwetting surfaces, which induce Laplace pressure based on the bubble radius differences in confined states. Although this method has successfully demonstrated bubble manipulations in various geometries, it has inevitably shown some critical limitations; gas bubbles move unidirectionally from tip to root direction and cease their movements upon reaching unconfined states. This unidirectional and local bubble transport restrains the method's applicability to many fields, and overcoming this obstacle still remains an enormous challenge. Herein, a magnetocontrollable lubricant‐infused surface (MCLIS) is introduced as a key solution to this issue. MCLISs manipulate the adhesion of gas bubbles by controlling magneto‐responsive microwire alignments and rendering two reversible adhesion states, sticky (upright) and slippery (laying wires). This unique characteristic of MCLISs enables the bidirectional and geometry‐unrestricted transportation of bubbles by the wire geometry‐gradient force (Fwgg) generated at sticky–slippery interfaces. Furthermore, this novel magnetic responsive surface supports anti‐buoyancy transport and presents promising applications in microreactors and optical laser shutters in aqueous media.

Stress - strain behaviour of confined nano silica-based concrete

In the present study, the stress-stain behaviour of confined concrete made with nano-silica (nano-SiO2) were taken up. The stress-strain behaviour was studied for the M30 and M50 grades nano-silica (nano-SiO2) concrete mixes confined with steel rebars. The confinement was given in the form of steel hoops in the cylinders, 3 hoops (0.8%), 4 hoops (1.1%), 5 hoops (1.3%) and 6 hoops (1.6%). The addition of nano-silica (nano-SiO2) along with confinement of concrete with steel hoops enhanced the compressive strength, indicating further confinement effect in the concrete. It is observed that the addition of nano-silica (nano-SiO2) is helpful in lower confinements only. Beyond 1.1% confinement, doesn’t show any effect on compressive strengths. From the stress-strain behaviour of all types of concrete mixes, it is concluded that the ultimate load-carrying capacity and strains at peak stresses are more in nano-silica (nano-SiO2) concrete with steel hoops for mixes up to 1.1% confinement. The addition of nano-silica (nano-SiO2) to concrete has increased the ductility in both confined and unconfined states

Studies on stress- strain behaviour of fibre reinforced self-compacting concrete in confined state

In the present study, the stress-stain behaviour of self-compacting concrete (SCC) and fibre reinforced self-compacting concrete (FRSCC) were taken up. The stress-strain behaviour was studied for the SCC and FRSCC mixes in unconfined and confined states. The confinement was given in the form of steel hoops in the cylinders, 3 hoops (0.8%), 4 hoops (1.1%), 5 hoops (1.3%) and 6 hoops (1.6%). The addition of fibres along with confinement of FRSCC with steel hoops enhanced the compressive strength, indicating further confinement effect in the FRSCC. It is observed that the addition of fibres is helpful in lower confinements only. Beyond 1.1% confinement, the addition of any type of fibres doesn’t show any effect on compressive strengths. From the stress-strain behaviour of all types of FRSCC, it is concluded that the ultimate load-carrying capacity and strains at peak stresses are more in SFRSCC and HFRSCC for mixes up to 1.1% confinement. The addition of fibres to SCC has increased the ductility in both confined and unconfined states

Studies on stress-strain behaviour of concrete mixes confined with BFRP rebars

In the present study, the stress-stain behaviour of confined concrete made with basalt fibre reinforced polymer bars (BFRP) were taken up. The stress-strain behaviour was studied for the concrete mixes confined with steel rebars and BFRP rebars. The confinement was given in the form of steel hoops in the cylinders, 3 hoops (0.8%), 4 hoops (1.1%), 5 hoops (1.3%) and 6 hoops (1.6%). The addition of basalt fibres along with confinement of concrete with steel and BFRP hoops enhanced the compressive strength, indicating further confinement effect in the concrete. It is observed that the addition of fibres is helpful in lower confinements only. Beyond 1.1% confinement, the addition of any type of basalt fibres doesn’t show any effect on compressive strengths. From the stress-strain behaviour of all types of concrete mixes, it is concluded that the ultimate load-carrying capacity and strains at peak stresses are more in concrete with BFRP hoops for mixes up to 1.1% confinement. The addition of basalt fibres to concrete has increased the ductility in both confined and unconfined states

Insight into the Electrical Double Layer of Ionic Liquids Revealed through Its Temporal Evolution

AbstractIonic liquids (ILs) are proposed as potentially ideal electrolytes for use in electrical double layer capacitors. However, recent discoveries of long‐range electrostatic screening in ILs have revealed that this understanding of the electrical double layer in highly concentrated solutions is still incomplete. Through precise time‐dependent measurements of wide‐angle X‐ray scattering and surface forces, novel molecular insight into their electrical double layer is provided. An ultraslow evolution of the nanostructure of three imidazolium ILs is observed, which reflects the reorganization of the ions in confined and unconfined (bulk) states. The observed phase transformation in the bulk consists of the ILs ordering over at least 20 h, reflected in an expansion or contraction of the spacing between the ions organized in domains of ≈10 nm. This transformation justifies the evolution of the electrical double layer measured in force measurements. Subtle differences between the ILs arise from the intricate balance between electrostatic and non‐electrostatic interactions. This work reveals a new time scale of the evolution of the IL structure and offers a new perspective for understanding the electrical double layer in ILs, with implications on diverse areas of inquiry, such as energy storage, lubrication, as well as micro‐ and nanoelectronics devices.

In situ high-energy X-ray diffraction study of thermally-activated martensitic transformation far below room temperature in CuZr-based bulk metallic glass composites

Abstract The martensitic transformation within B2 phase plays a critical role for the ductility of CuZr-based bulk metallic glass (BMG) composites, yet the underlying mechanism for the martensitic transformation process needs further investigations. Here, we found that the onset temperature of the thermally-activated martensitic transformation for CuZr-based BMG composites was reduced to 162.7 ± 2.5 K, which is far lower than those of polycrystalline samples, due to the stabilization of the austenitic phase induced by crystalline-amorphous interfaces. In situ high-energy X-ray diffraction measurements (HEXRD) further demonstrate that the thermally-activated martensitic transformation is governed by an extremely incomplete martensitic transformation from B2 to B19’ and B33 phases without the decomposition of B2 phase which generally appears in polycrystalline samples. Due to unconfined stress states during the thermally-activated martensitic transformation, B33 phase forms more early during thermal process than deformation process. The present study provides a further understanding on the martensitic transformation behaviors of shape memory type CuZr-based BMG composites.

Effects of freeze-thaw cycles on the unconfined compressive strength of straw fiber-reinforced soil

Although natural fibers can improve the strength behavior of frozen-thawed soil, the reinforcing mechanism is still not fully understood. To investigate the effects of freeze-thaw cycles on the strength of natural fiber-reinforced soil, unconfined compression tests, single-fiber pull-out tests and scanning electron microscopy (SEM) tests under 0, 3, 5, 10, 15, and 20 freeze-thaw cycles were conducted on cotton straw fiber-reinforced soil. It was found that the unconfined compressive strength (UCS) of fiber-reinforced soil decreases exponentially with the number of freeze-thaw cycles. In addition, fiber reinforcement weakens the softening degree of frozen-thawed soil under unconfined states. The UCS reduction in fiber-reinforced soil under freeze-thaw conditions is smaller than the strength reduction at the fiber-soil interface because fiber reinforcement is mainly governed not only by the fiber-soil interface but also by the spatial stress network established by discrete fibers. The complex spatial stress network, which improves the reinforcement of the fibers, is monitored by SEM after freeze-thaw cycles.

Escape of a Driven Quantum Josephson Circuit into Unconfined States

Josephson circuits have been ideal systems to study complex non-linear dynamics which can lead to chaotic behavior and instabilities. More recently, Josephson circuits in the quantum regime, particularly in the presence of microwave drives, have demonstrated their ability to emulate a variety of Hamiltonians that are useful for the processing of quantum information. In this paper we show that these drives lead to an instability which results in the escape of the circuit mode into states that are not confined by the Josephson cosine potential. We observe this escape in a ubiquitous circuit: a transmon embedded in a 3D cavity. When the transmon occupies these free-particle-like states, the circuit behaves as though the junction had been removed, and all non-linearities are lost. This work deepens our understanding of strongly driven Josephson circuits, which is important for fundamental and application perspectives, such as the engineering of Hamiltonians by parametric pumping.

CO2 sorption induced damage in coals in unconfined and confined stress states: A micrometer to core scale investigation

Gas sorption in coal, in particular CO2, is known to cause swelling and internal structural change or damage. For instance, CO2 adsorption on coal causes swelling which in turn can close the fractures or cleats whereas its desorption can open pre-existing fractures as well as create new fractures, thus enhancing gas flow paths in coal seams. Gas release and the associated induced damage are relevant for several applications such as coal burst in coal mining operations and for geological sequestration of CO2 into coal seams to reduce both the carbon footprint and increase the efficiency of energy extraction. However, the sorption-induced internal structural damage in coal, in particular the link between the micro-scale damage phenomena to macro-scale processes in confined and unconfined stress states, is not yet fully understood.We carried out a series of experiments to study the potential sorption-induced damage in both confined and unconfined stress states at micro (μm) and macro (cm) scale. 3D images, obtained by X-ray microcomputed tomography (micro-CT) technique, showed that in the unconfined stress state, adsorption of CO2 closes some pre-existing fractures while new fractures form in the specimen of coal. This is well supported by high pressure CO2 adsorption analyses that were independently conducted. After CO2 release, the overall fracture intensity, defined as the area of fractures per volume of rock mass, was considerably increased by opening both pre-existing fractures together with new fractures. In the confined condition, the gas adsorption was significantly lower confirming the closure of the initial fractures by swelling without creation of induced fractures. However, the gas release under shearing stress was significantly higher showing that the shearing stress causes further damage assisted by gas release and its induced micro-structural damage.

Experimental demonstration of a Rydberg-atom beam splitter

Inhomogeneous electric fields generated above two-dimensional electrode structures have been used to transversely split beams of helium Rydberg atoms into pairs of spatially separated components. The atomic beams had initial longitudinal speeds of between 1700 and 2000 m/s and were prepared in Rydberg states with principle quantum number $n=52$ and electric dipole moments of up to 8700 D by resonance-enhanced two-color two-photon laser excitation from the metastable 1s2s $^3$S$_1$ level. Upon exiting the beam splitter the ensembles of Rydberg atoms were separated by up to 15.6 mm and were detected by pulsed electric field ionization. Effects of amplitude modulation of the electric fields of the beam splitter were shown to cause particle losses through transitions into unconfined Rydberg-Stark states.

Dimensional Metrology of Cell-matrix Interactions in 3D Microscale Fibrous Substrates

The significant potential of engineered tissue models is bounded by the current lack of robust scalable additive biomanufacturing processes that reliably capture the cell's structural microenvironments. To address this bottleneck, a melt electrospinning writing system is designed to fabricate 3D fibrous substrates within a tight cellular dimensional scale window. The biological relevance of the produced 3D experimental substrates over its 2D monolayer controls is demonstrated with respect to cell morphology. Cell confinement states are quantitatively characterized using an automated single-cell bioimage data analysis workflow. A multidimensional data set composed of size, shape and distribution related metrics of cellular and sub-cellular focal adhesions is extracted to build a classifier that can, with 91-93% classification accuracy, distinguish cell shape phenotypes in 3D confined versus 2D unconfined cell states.

A multi-band, multi-level, multi-electron model for efficient FDTD simulations of electromagnetic interactions with semiconductor quantum wells

We report a new computational model for simulations of electromagnetic interactions with semiconductor quantum well(s) (SQW) in complex electromagnetic geometries using the finite-difference time-domain method. The presented model is based on an approach of spanning a large number of electron transverse momentum states in each SQW sub-band (multi-band) with a small number of discrete multi-electron states (multi-level, multi-electron). This enables accurate and efficient two-dimensional (2-D) and three-dimensional (3-D) simulations of nanophotonic devices with SQW active media. The model includes the following features: (1) Optically induced interband transitions between various SQW conduction and heavy-hole or light-hole sub-bands are considered. (2) Novel intra sub-band and inter sub-band transition terms are derived to thermalize the electron and hole occupational distributions to the correct Fermi-Dirac distributions. (3) The terms in (2) result in an explicit update scheme which circumvents numerically cumbersome iterative procedures. This significantly augments computational efficiency. (4) Explicit update terms to account for carrier leakage to unconfined states are derived, which thermalize the bulk and SQW populations to a common quasi-equilibrium Fermi-Dirac distribution. (5) Auger recombination and intervalence band absorption are included. The model is validated by comparisons to analytic band-filling calculations, simulations of SQW optical gain spectra, and photonic crystal lasers.

Optical Transitions between Confined and Unconfined States in p-Type Asymmetric GaAs/InGaAs/AlGaAs QW Structures

We present contactless surface photovoltage spectroscopy and photoreflectance studies of 10 nm wide, p-type doped asymmetric GaAs/InGaAs/AlGaAs quantum well structures. The MBE grown structures differ in spacer thickness between the quantum well and the reservoir of holes. The doping causes that quantum well is placed in electric field. The surface photovoltage spectroscopy measurements gave us detailed information about the optical transitions between confined states and between confined and unconfined states. The comparison of experimental and numerical analysis allows us to identify all features present in the surface photovoltage spectroscopy and photoreflectance spectra. It has been found that spacer layer thickness has significant influence on surface photovoltage spectroscopy spectra.

Confined-Unconfined Changes above Longwall Coal Mining Due to Increases in Fracture Porosity

Subsidence and strata movement above longwall (total extraction) coal mines produce complex hydrologic responses that can occur independently of drainage to the mine. One response is dewatering from confined to unconfined conditions in bedrock aquifers as a result of loss of water into new void space created by fracture and bedding separations. This dewatering process has been little studied but accounts for several hydraulic and geochemical effects of longwall mining. This article presents a conceptual model of the process and reviews evidence from case studies. Confined bedrock aquifers in subsiding zones exhibit dramatically steep head drops because of the low value of confined storage coefficients relative to the volume of water drained into the new fracture void space. The aquifer changes rapidly to an unconfined condition. Tight units to which air entry is restricted may even develop negative water pressures. In the unconfined state, sulfide minerals present in the strata readily oxidize to soluble hydrated sulfates. When the aquifer re-saturates, these salts are rapidly mobilized and produce a flush of increased sulfate and total dissolved solids (TDS) levels. Observations made in our previous studies in Illinois are consistent with the confined-unconfined model and include rapid head drops, changes to unconfined conditions, and increases in sulfate and TDS during re-saturation of a sandstone aquifer. Studies reported from the Appalachian coalfield show aspects consistent with the model, but in this high-relief fractured setting it is often difficult to distinguish aquifers from aquitards, confined from unconfined states, and the fracture-porosity cause of head drops from several others that occur during mine subsidence.

Analysis of the Optical Gain Characteristics of Semiconductor Quantum-Dash Materials Including the Band Structure Modifications Due to the Wetting Layer

We present a numerical model for the calculation of the opto-electronic properties of a semiconductor InAs-InAlGaAs quantum dash active material including the presence of the wetting layer (WL), formed at the bottom of the dashes, and the quantum mechanical coupling among dashes caused by the high density of the InAs islands. The model calculates self-consistently the conduction and valence band energy diagram of the confined and unconfined states, the corresponding density of states, the electron and hole wavefunctions and the gain spectra. The results obtained are also compared with a more simple model that consider dashes as isolated and without the WL. The comparison evidences the role of the WL in limiting the gain performance such as the maximum gain, the differential gain and the optical gain bandwidth. The numerical tool is then used to design an improved quantum dash material, which allows to overcome these gain limitations even in presence of the WL and the high dash density.

Comparative study of confinement models for high-strength concrete columns

The analysis of structural members requires an analytical model for the full stress-strain relationship of concrete in compression both in confined and unconfined states. Many empirical confinement models have been reported in the literature during the last three decades. The models developed for normal strength concrete are not applicable to high-strength concrete, because they overestimate the ductility of high-strength concrete. This paper critically reviews the various proposed stress-strain models for confined high-strength concrete columns. There are very few models for confined concrete with compressive strength in the range of 60–120 MPa. The main objective of the present study is to examine the capabilities of the various models to predict the actual experimental behaviour of confined concrete columns with concrete strengths falling in this range. To this end, twenty-two test specimens were chosen from the reported experimental studies in the literature and their stress-strain curves were compared with the ones predicted by the various models. It was shown that the Legeron and Paultre model estimates the actual practical curves more closely in comparison with other models employed in this study.

Comparative study of confinement models for high-strength concrete columns

The analysis of structural members requires an analytical model for the full stress-strain relationship of concrete in compression both in confined and unconfined states. Many empirical confinement models have been reported in the literature during the last three decades. The models developed for normal strength concrete are not applicable to high-strength concrete, because they overestimate the ductility of high-strength concrete. This paper critically reviews the various proposed stress-strain models for confined high-strength concrete columns. There are very few models for confined concrete with compressive strength in the range of 60–120 MPa. The main objective of the present study is to examine the capabilities of the various models to predict the actual experimental behaviour of confined concrete columns with concrete strengths falling in this range. To this end, twenty-two test specimens were chosen from the reported experimental studies in the literature and their stress-strain curves were compared with the ones predicted by the various models. It was shown that the Legeron and Paultre model estimates the actual practical curves more closely in comparison with other models employed in this study.

Plasma heating in highly excited GaN/AlGaN multiple quantum wells

Time-resolved photoluminescence (PL) spectroscopy was used to investigate carrier distributions in a GaN/AlGaN multiple quantum well (MQW) sample under high excitation intensities necessary to achieve lasing threshold. Room temperature PL spectra showed optical transitions involving both confined and unconfined states in the quantum well structure. Analysis of the experimental results using a microscopic theory, indicates that at high excitation the carrier distributions are characterized by plasma temperatures which are significantly higher than the lattice temperature. The implications of our findings on GaN MQW laser design are also discussed.