Reversible Shift Research Articles

Hydrogel films engineered in a mesoscopically ordered structure and responsive to ethanol vapors

Responsive hydrogels filling the interstitial spaces of photonic crystals can form mesoscopically structured materials, which exhibit reversible shifts in the Bragg diffracted light as a response of environmental changes. These materials can be used to generate chemical or biochemical sensors. The present work reports on the synthesis and characterization of ethanol responsive hydrogels that can be used in the design of novel breathalyzers. The dynamic mechanical behavior of the macroscopic hydrogels and their swelling features in the presence of different liquids or vapors have been investigated to orientate the choice of the best responsive material and curing process. The swelling behavior of a selected hydrogel embedding the photonic crystal made of polystyrene nanoparticles as function of the concentration of ethanol vapor was studied through UV–Vis optical transmission spectroscopy and compared to the behavior of the macrogel analogue.

Role of Zinc and Niobium in the Giant Piezoelectric Response of PbZn1/3Nb2/3O3

Relaxor ferroelectric perovskites are highly polarizable and can exhibit giant coupling between elastic strain and an applied electric field. Here, we report an in situ extended X-ray absorption fine structure (EXAFS) study of a PbZn1/3Nb2/3O3 (PZN) single crystal as a function of the electric field. We show that the strong dipoles in the NbO6 octahedra bonds are aligned along the four ⟨011⟩ directions close to the orientation of the electric field, while a small reversible polar shift occurs for Zn in the direction of the electric field, i.e., positive or negative. This reversible Zn–O polar shift is proposed to play an important role in both the “easy” switching of the ferroelectric polarization and the giant piezoelectric effect in PZN.

Hot Topics—Hidden hearing loss: Permanent cochlear-nerve degeneration after temporary noise-induced threshold shift

The classic view of sensorineural hearing loss (SNHL) is that the “primary” targets are hair cells, and that cochlear-nerve loss is “secondary” to hair cell degeneration. Our work in mouse and guinea pig has challenged that view. In noise-induced hearing loss, exposures causing only reversible threshold shifts (and no hair cell loss) nevertheless cause permanent loss of >50% of cochlear-nerve/hair-cell synapses. Similarly, in age-related hearing loss, degeneration of cochlear synapses precedes both hair cell loss and threshold elevation. This primary neural degeneration has remained hidden for two reasons: (1) the spiral ganglion cells, the cochlear neural elements commonly assessed in studies of SNHL, survive for years despite loss of synaptic connection with hair cells, and (2) the degeneration is selective for cochlear-nerve fibers with high thresholds. Although not required for threshold detection in quiet (e.g., threshold audiometry, auditory brainstem response threshold), these high-threshold fibers are critical for hearing in noisy environments. Our research suggests that (1) primary neural degeneration is an important contributor to the perceptual handicap in SNHL, and (2) noise exposure guidelines should be re-evaluated, as they are based on the faulty premise that threshold audiograms are the most sensitive measures of noise damage.

Rational Design of Synthetic Nanoparticles with a Large Reversible Shift of Acid Dissociation Constants: Proton Imprinting in Stimuli Responsive Nanogel Particles

Rational Design of Synthetic Nanoparticles with a Large Reversible Shift of Acid Dissociation Constants: Proton Imprinting in Stimuli Responsive Nanogel Particles

Variation of exciton emissions of ZnO whiskers reversibly tuned by axial tensile strain

Applying strain on semiconductors is a powerful method to modulate its electronic structures and optical properties. In this study, the behavior of liquid-nitrogen exciton emissions and the longitudinal optical phonon-exciton interactions of tensile strained [0001]-orientated ZnO whiskers were investigated using in situ cathodoluminescence spectroscopy. It has been found that, under the axial tensile strain, various exciton emissions shift to the long wavelength and their shifts have a linear relationship with the applied strain. This linear relationship and reversible shift suggest that the strain plays a dominating role in manipulating light emissions of axially strained ZnO whiskers.

X-Ray Diffraction and Vibrational Spectroscopic Characteristics of Hydroxylclinohumite from Ruby-Bearing Marbles (Luc Yen District, Vietnam)

A honey-yellow hydroxylclinohumite from ruby-bearing marbles of the Luc Yen district in northern Vietnam was characterized by electron microprobe (EPMA), single-crystal X-ray diffraction (XRD), micro-Raman, and Fourier-transform infrared (FTIR) spectroscopy. The studied crystals correspond to nearly ideal clinohumite with the structural formula 4[Mg2SiO4]·[(Mg,Fe,Ti)(OH,F)2] and roughly equal F and OH proportions. Crystal structure analysis showed Ti substitution for Mg only at the Mg3 site. A Fourier-difference map revealed one hydrogen site associated with ninth oxygen atom. The calculated O–H bond distance was shorter than that in other natural clinohumites. FTIR revealed bands corresponding to combination of OH-stretching with Mg–OH and/or Fe–OH bending modes, combinations of OH−and Fe–OH vibrations, combination of fundamental bands of the Si–OH bonding, combination of OH−and Si–OH vibrations, and first (2νOH) and the second (3νOH) overtones of the OH-stretching vibration mode. Two groups of OH-stretching vibration and FTIR absorption bands at 3390–3420 cm−1and 3560–3580 cm−1show reversible temperature-dependent shift. The low-frequency bands absent in pure synthetic hydroxylclinohumites are assigned to OH-planar defects caused by Ti-for-Mg substitution.

Impact of local compressive stress on the optical transitions of single organic dye molecules

The ability to mechanically control the optical properties of individual molecules is a grand challenge in nanoscience and could enable the manipulation of chemical reactivity at the single-molecule level. In the past, light has been used to alter the emission wavelength of individual molecules or modulate the energy transfer quantum yield between them. Furthermore, tensile stress has been applied to study the force dependence of protein folding/unfolding and of the chemistry and photochemistry of single molecules, although in these mechanical experiments the strength of the weakest bond limits the amount of applicable force. Here, we show that compressive stress modifies the photophysical properties of individual dye molecules. We use an atomic force microscope tip to prod individual molecules adsorbed on a surface and follow the effect of the applied force on the electronic states of the molecule by fluorescence spectroscopy. Applying a localized compressive force on an isolated molecule induces a stress that is redistributed throughout the structure. Accordingly, we observe reversible spectral shifts and even shifts that persist after retracting the microscope tip, which we attribute to transitions to metastable states. Using quantum-mechanical calculations, we show that these photophysical changes can be associated with transitions among the different possible conformers of the adsorbed molecule.

Design of a reversible single precision floating point subtractor

In recent years, Reversible logic has emerged as a major area of research due to its ability to reduce the power dissipation which is the main requirement in the low power digital circuit design. It has wide applications like low power CMOS design, Nano-technology, Digital signal processing, Communication, DNA computing and Optical computing. Floating-point operations are needed very frequently in nearly all computing disciplines, and studies have shown floating-point addition/subtraction to be the most used floating-point operation. However, few designs exist on efficient reversible BCD subtractors but no work on reversible floating point subtractor. In this paper, it is proposed to present an efficient reversible single precision floating-point subtractor. The proposed design requires reversible designs of an 8-bit and a 24-bit comparator unit, an 8-bit and a 24-bit subtractor, and a normalization unit. For normalization, a 24-bit Reversible Leading Zero Detector and a 24-bit reversible shift register is implemented to shift the mantissas. To realize a reversible 1-bit comparator, in this paper, two new 3x3 reversible gates are proposed The proposed reversible 1-bit comparator is better and optimized in terms of the number of reversible gates used, the number of transistor count and the number of garbage outputs. The proposed work is analysed in terms of number of reversible gates, garbage outputs, constant inputs and quantum costs. Using these modules, an efficient design of a reversible single precision floating point subtractor is proposed. Proposed circuits have been simulated using Modelsim and synthesized using Xilinx Virtex5vlx30tff665-3. The total on-chip power consumed by the proposed 32-bit reversible floating point subtractor is 0.410 W.

Stress Shift to Tensile Side by the Interruption of Deposition during Al and Cr Film Processing

When an average stress in metallic thin film was measured as a function of the film thickness during real time deposition, three distinct stress stages of initial compressive, tensile, and compressive were reported to occur for metals with relatively high mobility. A reversible stress shift to the tensile side was observed due to an abrupt interruption of deposition at the compressive stage. The stress shift occurred rapidly in the beginning and rather slowly later, to reach a saturation value. The current study explored the stress shift caused by an abrupt interruption of deposition with focus on the state and magnitude of the thin film stress for the two metals, Al and Cr, with different levels of mobility. For Cr with relatively low mobility, only tensile stress was observed at room temperature deposition, but the three stress stages were observed for Cr deposited at 300°C. It is argued that mobility is a possible factor for the stress evolution mode of the thin film as the diffusivity of Cr at 300°C has a similar order of magnitude as that of Al at the room temperature. No stress shift was observed when deposition interruption occurred at the tensile stress state, but the shift was observed only at the compressive stress state for both Al and Cr. The total amount of stress shift increased as the magnitude of compressive stress at the point of interruption increased for Al. [doi:10.2320/matertrans.M2014207]

Peptide Thioester Formation via an Intramolecular N to S Acyl Shift for Peptide Ligation.

In chemical protein synthesis, peptide building blocks are prepared by solid-phase peptide synthesis (SPPS), and then connected by chemical ligation methods. The peptide thioester is one of key building blocks used in chemical protein synthesis, and improvements in the Fmoc SPPS procedure for preparing such thioesters would be highly desirable. In this review we focus on a method for peptide thioester synthesis based on the use of an intramolecular N to S acyl shift reaction as a key reaction. Amide and thioester forms at the thiol-containing residue are in equilibrium as a result of a reversible intramolecular acyl shift, which is detectable by 13C NMR. The amide form is favored under neutral conditions, while the thioester predominates under acidic conditions. Thiol auxiliaries can be employed to facilitate the formation of a thioester from an amide via an intramolecular N-S acyl shift, and the peptide thioester is formed after intermolecular transthioesterification in the presence of excess amounts of thiols. Even under neutral conditions, thiol auxiliary-containing peptides can be ligated with a cysteinyl peptide via an intramolecular N-S acyl shift, followed by native chemical ligation (NCL) in a one-pot reaction. These procedures can be applied to the chemical synthesis of proteins which are post-translationally modified.

Bistable Parvalbumin Circuits Pivotal for Brain Plasticity

Experience shapes brain function throughout life to varying degrees. In a recent issue of Nature, Donato etal. identify reversible shifts in focal parvalbumin cell state during adult learning, placing it on a mechanistic continuum with developmental critical periods. A disinhibitory microcircuit controls the plasticity switch to modulate memory formation.

Luminescent thermochromism in potassium-alumina-borate glass with copper-containing molecular clusters at elevated temperatures

It is experimentally shown that a considerable luminescent thermochromic effect occurs in potassium-alumina-borate (PAB) glasses with copper-containing molecular clusters. This effect is manifested in a reversible blue spectral shift of luminescence band about 100nm and its narrowing, with negligible change of luminescence amplitude in maximum during heating from 20 up to 300°C. Luminescence and excitation spectra of PAB glass at different temperatures are presented. It is shown that the temperature rise results in a red spectral shift of excitation bands and in their broadening.

Parvalbumin-expressing basket-cell network plasticity induced by experience regulates adult learning

Learning and memory processes can be influenced by recent experience, but the mechanisms involved are poorly understood. Enhanced plasticity during critical periods of early life is linked to differentiating parvalbumin (PV)-interneuron networks, suggesting that recent experience may modulate learning by targeting the differentiation state of PV neurons in the adult. Here we show that environmental enrichment and Pavlovian contextual fear conditioning induce opposite, sustained and reversible hippocampal PV-network configurations in adult mice. Specifically, enrichment promotes the emergence of large fractions of low-differentiation (low PV and GAD67 expression) basket cells with low excitatory-to-inhibitory synaptic-density ratios, whereas fear conditioning leads to large fractions of high-differentiation (high PV and GAD67 expression) basket cells with high excitatory-to-inhibitory synaptic-density ratios. Pharmacogenetic inhibition or activation of PV neurons was sufficient to induce such opposite low-PV-network or high-PV-network configurations, respectively. The low-PV-network configuration enhanced structural synaptic plasticity, and memory consolidation and retrieval, whereas these were reduced by the high-PV-network configuration. We then show that maze navigation learning induces a hippocampal low-PV-network configuration paralleled by enhanced memory and structural synaptic plasticity throughout training, followed by a shift to a high-PV-network configuration after learning completion. The shift to a low-PV-network configuration specifically involved increased vasoactive intestinal polypeptide (VIP)-positive GABAergic boutons and synaptic transmission onto PV neurons. Closely comparable low- and high-PV-network configurations involving VIP boutons were specifically induced in primary motor cortex upon rotarod motor learning. These results uncover a network plasticity mechanism induced after learning through VIP-PV microcircuit modulation, and involving large, sustained and reversible shifts in the configuration of PV basket-cell networks in the adult. This novel form of experience-related plasticity in the adult modulates memory consolidation, retrieval and learning, and might be harnessed for therapeutic strategies to promote cognitive enhancement and neuroprotection.

In situ electronic structural study of VO2 thin film across the metal—insulator transition

The in situ valence band photoemission spectrum (PES) and X-ray absorption spectrum (XAS) at V LII — LIII edges of the VO2 thin film, which is prepared by pulsed laser deposition, are measured across the metal—insulator transition (MIT) temperature (TMIT = 67 °C). The spectra show evidence for changes in the electronic structure depending on temperature. Across the TMIT, pure V 3d characteristic d‖ and O 2p-V 3d hybridization characteristic πpd, σpd bands vary in binding energy position and density of state distributions. The XAS reveals a temperature-dependent reversible energy shift at the V LIII-edge. The PES and XAS results imply a synergetic energy position shift of occupied valence bands and unoccupied conduction band states across the phase transition. A joint inspection of the PES and XAS results shows that the MIT is not a one-step process, instead it is a process in which a semiconductor phase appears as an intermediate state. The final metallic phase from insulating state is reached through insulator—semiconductor, semiconductor—metal processes, and vice versa. The conventional MIT at around the TMIT = 67 °C is actually a semiconductor—insulator transformation point.

Local temperature determination in power loaded surface acoustic wave structures using Raman spectroscopy

The temperature at the surface of surface acoustic wave (SAW) devices is a critical parameter not only for their design but also for the understanding of failure mechanisms like acoustomigration. We report about a contactless measurement method using Raman spectroscopy for the temperature determination on interdigital transducers (IDTs) of SAW test structures. A power load of up to 3.5 W/mm2 at an operating frequency of 130 MHz was used to generate travelling Rayleigh waves on a lithium niobate 128° YX substrate. Here, the local temperature on the surface between the finger electrodes of the IDT increases by 60 K. In addition to Raman spectroscopy, the reversible shift of the resonance frequency of the SAW test structure was used to determine and calibrate the local temperature of external loaded samples. These experiments show good agreement with temperatures obtained by Raman spectroscopy based evaluations.

Solution-Processed Barium Zirconate Titanate for Pentacene-Based Thin-Film Transistor and Memory

Pentacene-based organic thin-film transistors with solution-processed barium zirconate titanate dielectric layers are demonstrated. According to the programming/erasing operations, the devices exhibited memory characteristics, such as reversible threshold voltage shifts and nondestructive readout. In addition, the reliability of the memory devices was confirmed by data retention time and repeated switching cycles' endurance testing. In addition, the possible mechanism of the memory effect was also discussed. These results suggest that the devices could potentially be applied to nonvolatile memory applications in organic electronics.

Temperature response of the neuronal cytoskeleton mapped via atomic force and fluorescence microscopy

Neuronal cells change their growth properties in response to external physical stimuli such as variations in external temperature, stiffness of the growth substrate, or topographical guidance cues. Detailed knowledge of the mechanisms that control these biomechanical responses is necessary for understanding the basic principles that underlie neuronal growth and regeneration. Here, we present elasticity maps of living cortical neurons (embryonic rat) as a function of temperature, and correlate these maps to the locations of internal structural components of the cytoskeleton. Neurons display a significant increase in the average elastic modulus upon a decrease in ambient temperature from 37 to 25 °C. We demonstrate that the dominant mechanism by which the elasticity of the neurons changes in response to temperature is the stiffening of the actin components of the cytoskeleton induced by myosin II. We also report a reversible shift in the location and composition of the high-stiffness areas of the neuron cytoskeleton with temperature. At 37 °C the areas of the cell displaying high elastic modulus overlap with the tubulin-dense regions, while at 25 °C these high-stiffness areas correspond to the actin-dense regions of the cytoskeleton. These results demonstrate the importance of considering temperature effects when investigating cytoskeletal dynamics in cells.

Flexibly Tethered Dinuclear Zinc Complexes: A Solution to the Entropy Problem in CO2/Epoxide Copolymerization Catalysis?

Working in zinc: Kinetic investigations of a new zinc catalyst (see scheme) for the copolymerization of CO2 and epoxides show a reversible shift in the rate-determining step from epoxide ring opening to CO2 insertion, depending on the applied pressure. This shift is attributed to the similarity of the activation barriers and explains the exceptionally high activities for the copolymerization.

Feedbacks underlie the resilience of salt marshes and rapid reversal of consumer‐driven die‐off

Understanding ecosystem resilience to human impacts is critical for conservation and restoration. The large-scale die-off of New England salt marshes was triggered by overfishing and resulted from decades of runaway crab grazing. In 2009, however, cordgrass began to recover, decreasing die-off -40% by 2010. We used surveys and experiments to test whether plant-substrate feedbacks underlie marsh resilience. Initially, grazer-generated die-off swept through the cordgrass, creating exposed, stressful peat banks that inhibited plant growth. This desertification cycle broke when banks eroded and peat transitioned into mud with fewer herbivores, less grazing, and lower physical stress. Cordgrass reestablished in these areas through a feedback where it engineered a recovery zone by further ameliorating physical stresses and facilitating additional revegetation. Our results reveal that feedbacks can play a critical role in rapid, reversible ecosystem shifts associated with human impacts, and that the interplay of facilitative and consumer interactions should be incorporated into resilience theory.

Organic Field‐Effect Transistor Memory Devices Using Discrete Ferritin Nanoparticle‐Based Gate Dielectrics

Organic field-effect transistor (OFET) memory devices made using highly stable iron-storage protein nanoparticle (NP) multilayers and pentacene semiconductor materials are introduced. These transistor memory devices have nonvolatile memory properties that cause reversible shifts in the threshold voltage (Vth ) as a result of charge trapping and detrapping in the protein NP (i.e., the ferritin NP with a ferrihydrite phosphate core) gate dielectric layers rather than the metallic NP layers employed in conventional OFET memory devices. The protein NP-based OFET memory devices exhibit good programmable memory properties, namely, large memory window ΔVth (greater than 20 V), a fast switching speed (10 μs), high ON/OFF current ratio (above 10(4)), and good electrical reliability. The memory performance of the devices is significantly enhanced by molecular-level manipulation of the protein NP layers, and various biomaterials with heme Fe(III) /Fe(II) redox couples similar to a ferrihydrite phosphate core are also employed as charge storage dielectrics. Furthermore, when these protein NP multilayers are deposited onto poly(ethylene naphthalate) substrates coated with an indium tin oxide gate electrode and a 50-nm-thick high-k Al2 O3 gate dielectric layer, the approach is effectively extended to flexible protein transistor memory devices that have good electrical performance within a range of low operating voltages (<10 V) and reliable mechanical bending stability.