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A flexible TWDM PON system is proposed which allows pay-as-you-grow in capacity, supports load balancing among different ODNs, and achieves significant power saving at OLT. Integrated OLT transceiver in enhanced CFP module and low-cost tunable ONU transceiver in SFP+ module are developed, for the first time, for cost effective deployment of TWDM PONs. System experiments demonstrate error free performance with 36 dB power budget in a flexible TWDM PON test bed.

Aquasols containing silica nanoparticles with diameters of 75 to 95 nm were obtained directly by hydrolysis of 2 wt.% tetraethoxysilane (TEOS) in water in the presence of a non-ionic surfactant. The reaction was catalyzed by hydrochloric acid, ammonia, or sodium hydroxide. The particle size, which mainly depends on the concentration of TEOS in water, was determined by dynamic light scattering (DLS). Whereas the catalysts have almost no influence on the particle size, they very strongly affect the morphology of the silica particles formed. The dried SiO(2) particles obtained via the HCl-catalyzed reaction have film-forming properties and show no measurable BET surface area. SiO(2) particles prepared with ammonia as catalyst form nanoporous films on glass, and the BET surface area of the freeze-dried particles is 540 m(2)/g. Using sodium hydroxide as catalyst results in some agglomeration of uniform spherical particles with a BET surface area of 237 m(2)/g. (29)Si MAS NMR investigations of the freeze-dried particles provide information about the degree of condensation and the ratio of "free" hydroxyl groups. The silica aquasols described have a surprisingly high hydrophilizing effect on hydrophobic fibers (PP, PET). Silica nanoparticles of comparable diameters, prepared by the "Stöber method", dispersed in alcohol do not show any hydrophilizing properties worth to mention., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Individual single-walled carbon nanotube (SWCNT) field effect transistors (FETs) with a 2 nm thick silane-based organic self-assembled monolayer (SAM) gate dielectric have been manufactured. The FETs exhibit a unique combination of excellent device performance parameters. In particular, they operate with a gate-source voltage of only -1 V and exhibit good saturation, large transconductance, and small hysteresis (

Organic/silicon hybrid solar cells have attracted much interest due to their cheap fabrication process and simple device structure. A category of organic substances, Dibenzothiophene–Spirobifluorene–Dithiophene (DBBT-mTPA-DBT), comprises dibenzo [d,b] thiophene and 3-(3-methoxyphenyl)-6-(4-methoxyphenyl)-9H-Carbazole, which function as electron donors. In contrast, methanone is an electron acceptor, with an ∆Est of 3.19 eV. This work focused on hybrid solar cells based on the guest–host phenomena of DBBT-mTPA-DBT and CBP. Using a Si/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) hybrid solar cell with an ultra-thin Dibenzothiophene–Spirobifluorene–Dithienothiophene (DBBT-mTPA-DBT) interlayer between Si and Al led to a PCE of 17.5 ± 2.5%. The DBBT-mTPA-DBT interlayer substantially improved the Si/Al interface, reducing contact resistance from 6.5 × 10⁻1 Ω·cm2 to 3.5 × 10⁻2 Ω·cm2. This improvement increases electron transport efficiency from silicon to aluminum and reduces carrier recombination. The solar cell containing the DBBT-mTPA-DBT/Al double-layer cathode shows a 10.85% increase in power conversion efficiency relative to the standard Al cathode device. [ABSTRACT FROM AUTHOR]

Using Van Allen Probes observations from September 2012 to June 2019, we statistically investigate responses of the Earth's outer radiation belt electron phase space densities (PSDs) in the adiabatic invariant coordinates to isolated geomagnetic storms. Electron PSDs for μ = 50–5,000 MeV/G, covering energy range of seed, relativistic and ultra‐relativistic electrons, are calculated to evaluate three types of storm‐time PSD responses (i.e., enhancement, depletion, and no change). In statistics, the seed PSD variations are dominated by enhancement‐type events, the percentages of which increase from >50% for small storms (−50 nT < SYM‐Hmin ≤ −30 nT) to >70% for large storms (SYM‐Hmin ≤ −50 nT). The relativistic and ultra‐relativistic PSDs exhibit the three response types with comparable occurrence rates for small storms but present predominantly enhancement‐type variations (>50%) for large storms. Enhanced storm activity increases the enhancement‐type responses for seed PSDs at all L* and for relativistic and ultra‐relativistic PSDs at L* > 3.5. It also results in the increased depletion‐type response occurrence for relativistic and ultra‐relativistic PSDs at lower L*. Our results further indicate that the depletion‐type responses manifest evident dependence on the level of solar and geomagnetic activity and the μ‐value, implying complex physics accounting for outer zone electron losses. Improved knowledge of the storm‐time dynamics of outer radiation belt electron PSDs is valuable to in‐depth comprehension of various mechanisms responsible for the electron acceleration and loss. It has important implications for future simulations and forecasts of radiation belt electron variability, in particular, during geomagnetically disturbed periods. Plain Language Summary: Energetic electrons (>100 keV) are trapped by the Earth's outer radiation belt and exhibit dynamical responses due to an imbalance between acceleration and loss processes, especially during geomagnetically active conditions. Consequently, the electron fluxes can vary by a few orders of magnitude on timescales from a few hours to several days. However, the electron fluxes include both adiabatic and non‐adiabatic effects. By calculating electron phase space densities (PSDs) in adiabatic invariant coordinates (μ, K, L*), the adiabatic effects can be removed, and thus, the underlying mechanisms can be investigated. In this study, based on Van Allen Probes observations spanning September 2012 to June 2019, we statistically investigate the responses of the Earth's outer radiation belt electron PSDs to isolated geomagnetic storms. Using superposed epoch analysis, the dependences of electron PSD variations on μ, L* and geomagnetic storm magnitude, as well as solar and geomagnetic activities, are comprehensively analyzed. Our statistical results indicate that storm‐time responses of the Earth's outer radiation belt electron PSDs are strongly dependent on μ, L* and storm magnitude. The seed PSD variations are dominated by enhancement‐type events while relativistic and ultra‐relativistic electron PSD variations are strongly dependent on storm magnitude. Key Points: Storm‐time responses of Earth's outer radiation belt electron PSDs are strongly dependent on μ, L* and storm magnitudeSeed PSDs are mainly enhancement‐type variations while relativistic and ultra‐relativistic PSD variations depend on storm magnitudeEnhanced solar and geomagnetic activities facilitate enhancement‐type variations and manifest μ‐dependent depletion‐type variations [ABSTRACT FROM AUTHOR]

Acidic conditions affect the archaeological bone in the burial and in uncontrolled display and storage environment or due to improper restoration processes. Accordingly, bones become weak and fragile. This study aims to evaluate nano calcium propionate and nano styrene butyl acrylate (used for the first time in the treatment of bones) at different concentrations for deacidification and consolidation of fragile bones. New bone samples were prepared. Artificial accelerated aging (acid and heat) was applied to prepare aged untreated samples. Deacidification and consolidation processes using the materials mentioned above were applied. The analytical techniques used were transmission electron microscope (TEM) and thermal gravimetric analysis (TGA) were used for morphological and thermal stability investigation for the prepared nano styrene butyl acrylate copolymer and its calcium propionate nonocomposites, a digital microscope and scanning electron microscope (SEM) for investigation of the surface morphology, pH value measurement, change of color measurement, attenuated total reflection—Fourier transform infrared spectroscopy (ATR/FTIR), contact angle (wettability), and X-ray diffraction analysis for measurement of bone crystallinity. The results proved that acid-heat aging affected bone properties such as changes in surface morphology and color, decrease in pH value, and contact angle. Bone samples became more crystalline, and the chemical composition of bone was also affected. The treatment of aged untreated bone samples with the materials used in this study improved their properties, such as increasing the pH value and contact angle. The surface morphology, color change, and crystallinity of bone improved and became more stable. [ABSTRACT FROM AUTHOR]

A method for achieving the single-mode and efficient unidirectional emission of a whispering gallery mode (WGM) semiconductor laser is presented herein. Hybrid square-rectangular lasers (HSRLs) and hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Pérot (FP) cavity and a square or rhombus cavity microcavity are described. In addition, a transmitter optical subassembly (TOSA) based on an HSRRL chip was fabricated, which has a wide and continuous wavelength tuning range. Wavelength channels from 1555.75 nm to 1568.15 nm with a spacing of 50 GHz were demonstrated with a good side mode suppression ratio (SMSR) and good output power. These devices have the potential to meet the typical requirements of optical communication networks. [ABSTRACT FROM AUTHOR]

To date, the public health system has been impacted by the increasing costs of many diagnostic and therapeutic pathways due to limited resources. At the same time, we are constantly seeking to improve these paths through approaches aimed at personalized medicine. To achieve the required levels of diagnostic and therapeutic precision, it is necessary to integrate data from different sources and simulation platforms. Today, artificial intelligence (AI), machine learning (ML), and predictive computer models are more efficient at guiding decisions regarding better therapies and medical procedures. The evolution of these multiparametric and multimodal systems has led to the creation of digital twins (DTs). The goal of our review is to summarize AI applications in discovering new immunotherapies and developing predictive models for more precise immunotherapeutic decision-making. The findings from this literature review highlight that DTs, particularly predictive mathematical models, will be pivotal in advancing healthcare outcomes. Over time, DTs will indeed bring the benefits of diagnostic precision and personalized treatment to a broader spectrum of patients. [ABSTRACT FROM AUTHOR]

Cortical neurons are versatile and efficient coding units that develop strong preferences for specific stimulus characteristics. The sharpness of tuning and coding efficiency is hypothesized to be controlled by delicately balanced excitation and inhibition. These observations suggest a need for detailed co-tuning of excitatory and inhibitory populations. Theoretical studies have demonstrated that a combination of plasticity rules can lead to the emergence of excitation/inhibition (E/I) co-tuning in neurons driven by independent, low-noise signals. However, cortical signals are typically noisy and originate from highly recurrent networks, generating correlations in the inputs. This raises questions about the ability of plasticity mechanisms to self-organize co-tuned connectivity in neurons receiving noisy, correlated inputs. Here, we study the emergence of input selectivity and weight co-tuning in a neuron receiving input from a recurrent network via plastic feedforward connections. We demonstrate that while strong noise levels destroy the emergence of co-tuning in the readout neuron, introducing specific structures in the non-plastic pre-synaptic connectivity can re-establish it by generating a favourable correlation structure in the population activity. We further show that structured recurrent connectivity can impact the statistics in fully plastic recurrent networks, driving the formation of co-tuning in neurons that do not receive direct input from other areas. Our findings indicate that the network dynamics created by simple, biologically plausible structural connectivity patterns can enhance the ability of synaptic plasticity to learn input-output relationships in higher brain areas. Author summary: Many studies of learning in biological neural networks have focused on how plausible plasticity rules shape individual connections between neurons in a recurrent network or in feed-forward projections. However, in the latter case, the presynaptic network properties, such as clustered connectivity, strongly influence population dynamics and, thus, the learning process of the projections. Here, we aim to close this gap by showing how non-plastic network structure can strongly influence the outcomes of synaptic learning. We show that unstructured recurrent connectivity and the presence of noise can significantly reduce the ability of synaptic plasticity to separate presynaptic input populations and coordinate excitatory and inhibitory connection development, while the introduction of overlapping clustered structures in fixed or plastic recurrent connectivity can boost synaptic learning. Using Bayesian inference, we identify the optimal connectivity structures for a recurrent network and demonstrate the strong effects that relatively simple connectivity patterns can have on the ability of a network to learn via local plasticity. [ABSTRACT FROM AUTHOR]

Chorus waves induce both electron acceleration and loss. In this letter, we provide significantly improved models of electron lifetime due to interactions with chorus waves. The new models fill the gap that previous models have on some magnetic local time (MLT) sectors of the Earth's magnetosphere. This improvement is critical for modeling studies. The lifetime models developed using two different methods are valid for electrons with an energy range from 1 keV to 2 MeV. To facilitate the integration of these new models into different ring current and radiation belt codes, we parameterize the electron lifetime as a function of L $L$‐shell and electron kinetic energy at each MLT and geomagnetic activity (Kp). The parameterized electron lifetimes exhibit strong dependencies on L $L$‐shell, MLT, and energy. Simulations using these new models demonstrate improved agreement with satellite observations compared to simulations using previous models, advancing our understanding of electron dynamics in the magnetosphere. Plain Language Summary: There are a large number of energetic electrons trapped by our Earth's magnetic field in the near‐Earth space. The regions populated by these high energy electrons are called ring current and radiation belts. It is important to understand the dynamics of the energetic electrons because they can be dangerous to satellites and astronauts flying through these regions. Electromagnetic waves in these regions play an important role in the dynamic of ring current and radiation belt electrons. Among these waves, whistler mode chorus wave is an important wave that can cause both acceleration and loss of the energetic electrons. In our previous studies, we calculated diffusion coefficients to quantify the effect of chorus waves on the energetic electrons. Based on these diffusion coefficients, in this study, we estimate the lifetime of energetic electrons due to their interactions with chorus waves. To make this lifetime model more convenient to be used in different ring current and radiation belt models, we apply polynomial fits to the calculated lifetime. Our new lifetime model is more advanced than previous models, especially in the space coverage. We test the new models in simulations and the results agree better with satellite observations than the previous models do. Key Points: The new lifetime model provides extended space coverage in comparison to current widely used lifetime modelsSuch parameterized lifetimes are very significant for simulations of the dynamics of radiation belt and ring current electronsUsing the new electron lifetime model in simulations improves the agreement between the simulation results and the satellite observations [ABSTRACT FROM AUTHOR]

Passive optical network (PON) was designed in this paper. The design aim was to locate faulty line of service professionally without extra effort. In the literature, there were various PON-design methodologies. However, a design with fewer components and less faulty line tracking was a challenge. The suggested approach tried to overcome the leakage in the state-of-the-art, such that, the PON network would be able to serve forty-eight optical network units (ONUs). At the same time, the design has to have the capability to distinguish the dropped line of service straightforwardly. The design in this thesis mainly depends on the fiber Bragg gratings (FBGs) to create six-groups, in each group, there are eight-branches. Each branch serves as an end-user/customer point. The capacity of fault location was achieved for ONUs distanced/located as far as 20 Km from the central office (CO). There was only one optical spectrum analyser (OSA) inside the CO. This OSA employed to monitor the whole network groups, i.e., forty-eight branches/ONU were screened inside the CO to predict the fault location. The system is built using the OptiSystem software package version 14. [ABSTRACT FROM AUTHOR]

Space radiation is a notable hazard for long-duration human spaceflight1. Associated risks include cancer, cataracts, degenerative diseases2 and tissue reactions from large, acute exposures3. Space radiation originates from diverse sources, including galactic cosmic rays4, trapped-particle (Van Allen) belts5 and solar-particle events6. Previous radiation data are from the International Space Station and the Space Shuttle in low-Earth orbit protected by heavy shielding and Earth’s magnetic field7,8 and lightly shielded interplanetary robotic probes such as Mars Science Laboratory and Lunar Reconnaissance Orbiter9,10. Limited data from the Apollo missions11–13 and ground measurements with substantial caveats are also available14. Here we report radiation measurements from the heavily shielded Orion spacecraft on the uncrewed Artemis I lunar mission. At differing shielding locations inside the vehicle, a fourfold difference in dose rates was observed during proton-belt passes that are similar to large, reference solar-particle events. Interplanetary cosmic-ray dose equivalent rates in Orion were as much as 60% lower than previous observations9. Furthermore, a change in orientation of the spacecraft during the proton-belt transit resulted in a reduction of radiation dose rates of around 50%. These measurements validate the Orion for future crewed exploration and inform future human spaceflight mission design.Measurements from the heavily shielded Orion spacecraft during the uncrewed Artemis I mission show dose-rate reductions due to shielding and orientation for Van Allen belt crossings and quantify the interplanetary cosmic-ray radiation in a human-rated spacecraft. [ABSTRACT FROM AUTHOR]

Inflammatory diseases, including psoriasis, atherosclerosis, rheumatoid arthritis, and ulcerative colitis, are characterized by persistent inflammation. Moreover, the existing treatments for inflammatory diseases only provide temporary relief by controlling symptoms, and treatments of unstable and expensive. Therefore, new therapeutic solutions are urgently needed to address the underlying causes or symptoms of inflammatory diseases. Inflammation frequently coincides with a high level of (reactive oxygen species) ROS activation, serving as a fundamental element in numerous physiological and pathological phenotypes that can result in serious harm to the organism. Given its pivotal role in inflammation, oxidative stress, and ferroptosis, ROS represents a focal node for investigating the (nuclear factor E2-related factor 2) Nrf2 pathway and ferroptosis, both of which are intricately linked to ROS. Ferroptosis is mainly triggered by oxidative stress and involves iron-dependent lipid peroxidation. The transcription factor Nrf2 targets several genes within the ferroptosis pathway. Recent studies have shown that Nrf2 plays a significant role in three key ferroptosis-related routes, including the synthesis and metabolism of glutathione/glutathione peroxidase 4, iron metabolism, and lipid processes. As a result, ferroptosis-related treatments for inflammatory diseases have attracted much attention. Moreover, drugs targeting Nrf2 can be used to manage inflammatory conditions. This review aimed to assess ferroptosis regulation mechanism and the role of Nrf2 in ferroptosis inhibition. Therefore, this review article may provide the basis for more research regarding the treatment of inflammatory diseases through Nrf2-inhibited ferroptosis. [ABSTRACT FROM AUTHOR]

The Chaffee–Infante (CI) equation is a nonlinear equation that may be used to predict the complex dynamics of soliton propagation in a nonlinear optical medium. In this study, we elucidate soliton solutions of the CI equation by stochastic differential equations (SDEs) with the Wiener process. In excess of the modified auxiliary equation (MAE) method, we obtain new exact soliton solutions. By combining stochastic differential equations with the Wiener process, we explain the stochastic processes directing the magnitude of solitons within the basis of the CI equation, providing dynamic views on their behavior. The acquired solitary waves are depicted via 3D and 2D graphs to show their dynamics with and without Brownian motion. [ABSTRACT FROM AUTHOR]

The field of computer vision has long drawn inspiration from neuroscientific studies of the human and non-human primate visual system. The development of convolutional neural networks (CNNs), for example, was informed by the properties of simple and complex cells in early visual cortex. However, the computational relevance of oscillatory dynamics experimentally observed in the visual system are typically not considered in artificial neural networks (ANNs). Computational models of neocortical dynamics, on the other hand, rarely take inspiration from computer vision. Here, we combine methods from computational neuroscience and machine learning to implement multiplexing in a simple ANN using oscillatory dynamics. We first trained the network to classify individually presented letters. Post-training, we added temporal dynamics to the hidden layer, introducing refraction in the hidden units as well as pulsed inhibition mimicking neuronal alpha oscillations. Without these dynamics, the trained network correctly classified individual letters but produced a mixed output when presented with two letters simultaneously, indicating a bottleneck problem. When introducing refraction and oscillatory inhibition, the output nodes corresponding to the two stimuli activate sequentially, ordered along the phase of the inhibitory oscillations. Our model implements the idea that inhibitory oscillations segregate competing inputs in time. The results of our simulations pave the way for applications in deeper network architectures and more complicated machine learning problems. Author summary: Computer vision is a subfield of artificial intelligence focused on developing artificial neural networks (ANNs) that classify and generate images. Neuronal responses to visual features and the anatomical structure of the human visual system have traditionally inspired the development of computer vision models. The visual cortex also produces rhythmic activity that has long been suggested to support visual processes. However, there are only a few examples of ANNs embracing the temporal dynamics of the human brain. Here, we present a prototype of an ANN with biologically inspired dynamics—a dynamical ANN. We show that the dynamics enable the network to process two inputs simultaneously and read them out as a sequence, a task it has not been explicitly trained on. A crucial component of generating this dynamic output is a rhythm at about 10Hz, akin to the so-called alpha oscillations dominating human visual cortex. The oscillations rhythmically suppress activations in the network and stabilise its dynamics. The presented algorithm paves the way for applications in more complex machine learning problems. Moreover, we present several predictions that can be tested using established neuroscientific approaches. As such, the presented work contributes to both artificial intelligence and neuroscience. [ABSTRACT FROM AUTHOR]

This review covers the techniques, observations, and inferences of solar flare spectroscopy. It is not a spectroscopist's view of solar flares but rather a solar flare physicist's view of spectroscopy. Spectroscopy is carried out across the electromagnetic spectrum, but this review emphasizes the optical to soft X-ray part of the spectrum and discusses results from spectroscopy applied to the preflare, impulsive, and gradual phases, as well as a few highlights from modeling. The main spectroscopic signatures of the preflare phase are line broadening in optically thin ultraviolet to soft X-ray lines and small Doppler shifts in active region filaments that are becoming unstable. In the impulsive phase, fast upflows of heated plasma into the corona and slow downflows of cooler chromospheric plasma take place at the sites of strong chromospheric energy deposition. Radiation-hydrodynamic modeling of optically thick spectral lines gives a picture of an impulsive-phase chromosphere with a dense, heated layer deep in the atmosphere and an overlying, downward moving condensation that is partially optically thin. Gradual-phase observations show us the heated coronal plasma cooling and draining but also provide evidence for ongoing slow energy input and slow upflows in other locations. Interesting hints of non-Maxwellian and nonequilibrium plasmas have been found, along with possible evidence of plasma turbulence from line broadening. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the applicability of the data‐driven solar energetic particle (SEP) model, SOlar‐wind with FIeld‐lines and Energetic‐particles (SOFIE), to simulate the acceleration and transport processes of SEPs and make forecast of the energetic proton flux at energies ≥10 MeV that will be observed near 1 AU. The SOFIE model is built upon the Space Weather Modeling Framework developed at the University of Michigan. In SOFIE, the background solar wind plasma in the solar corona and interplanetary space is calculated by the Stream‐Aligned Aflvén Wave Solar‐atmosphere Model(‐Realtime) driven by the near‐real‐time hourly updated Global Oscillation Network Group solar magnetograms. In the background solar wind, coronal mass ejections (CMEs) are launched by placing an force‐imbalanced magnetic flux rope on top of the parent active region, using the Eruptive Event Generator using Gibson‐Low model. The acceleration and transport processes are modeled by the Multiple‐Field‐Line Advection Model for Particle Acceleration. In this work, nine SEP events (Solar Heliospheric and INterplanetary Environment challenge/campaign events) are modeled. The three modules in SOFIE are validated and evaluated by comparing with observations, including the steady‐state background solar wind properties, the white‐light image of the CMEs, and the flux of solar energetic protons, at energies of ≥10 MeV. Plain Language Summary: In this paper, we describe a physics‐based solar energetic particle (SEP) model, called Solar‐wind with FIeld‐lines and Energetic‐particles (SOFIE). This model is designed to simulate the acceleration and transport processes of SEPs in the solar atmosphere and interplanetary space. SOFIE is built on the Space Weather Modeling Framework developed at the University of Michigan. There are three modules in the SOFIE model, the background solar wind module, the coronal mass ejection (CME) initiation and propagation module, and the particle acceleration and transport module. The background solar wind plasma in the solar corona and interplanetary space is modeled by the Stream‐Aligned Aflvén Wave Solar‐atmosphere Model(‐Realtime) driven by the near‐real‐time hourly updated Global Oscillation Network Group solar magnetograms. In the background solar wind, the CMEs are launched by placing an force‐unbalanced magnetic flux rope on top of the active region, using the Eruptive Event Generator using Gibson‐Low configuration. The acceleration and transport processes are then modeled by the Multiple‐Field‐Line Advection Model for Particle Acceleration. Using SOFIE, we modeled nine historical SEP events. The performance of the model and its capability in making space radiation prediction is discussed. Key Points: The >10 MeV energetic protons can be predicted using the physics‐based model SOlar‐wind with FIeld‐lines and Energetic‐particles (SOFIE)The background of the acceleration and transport processes of energetic protons are resolved using data driven magnetohydrodynamic modelThe default and free parameters of the SOFIE model are evaluated [ABSTRACT FROM AUTHOR]

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The high-order microring filter has been proposed for a larger free spectral range (FSR) compared with the single microring filter; therefore, it has great potential to be used in wavelength division multiplexing (WDM) systems. In this article, we have designed and fabricated a second-order microring filter made up of two rings connected in series with two Ti thermal heaters deposited above them. The large FSR of 56.8 nm is obtained by decreasing the difference of the radii between the two series rings, achieving similar FSRs to that of higher-order filters but with a simpler and more compact design. The average electrical tuning efficiencies of the two heaters are 0.186 nm/mW and 0.207 nm/mW, and the center wavelength of the filter can be tuned over the entire FSR with an applied electrical power of less than 40 mW. [ABSTRACT FROM AUTHOR]

Self-assembled monolayers (SAMs) form highly ordered, stable dielectrics on conductive surfaces. Being able to attach larger-area contacts in a MIM (metal-insulator-metal) diode, their electrical properties can be determined. In this paper, the electrical conduction through thiolate SAMs of different alkyl chain lengths formed on gold surfaces were studied and discussed. The influence of the headgroup with respect to the surface quality and prevention of short circuits is investigated. Phenoxy terminated alkanethiols were found to form high quality SAMs with perfect insulating properties. Synthesis of the required terminally substituted long chain thiols have been developed. The I(V) characteristics of MIM structures formed with these SAMs are measured and simulated according to theoretical tunneling models for electrical conductivity through thin organic layers. SAM based electronic devices will become especially important for future nanoscale applications, where they can serve as insulators, gate dielectric of FETs, resistors, and capacitor structures.

In this paper, we analyze the degree of intramolecular charge transfer in a push-pull pi-conjugated system, 5-(dimethylamino)-5'-nitro-2,2'-bithiophene, from changes in frequencies and relative intensities of its strongest Raman scatterings in a bunch of solvents with different polarities. Density functional theory (DFT) was used as a support of the experimental study. Solvent effects on the molecular and electronic structures and on the vibrational properties were estimated by performing B3LYP/6-31G calculations within the framework of the polarized continuum model (PCM) developed by Tomasi. Calculations reveal that the molecule is highly polarized in the ground state and behaves as a very efficient photoinduced push-pull system. The polarization of the molecule strongly increases with solvent polarity and determines that the profile of the Raman spectra greatly changes from one solvent to another and in going to the solid. The strongest Raman scattering associated with the nu(sym)(NO(2)) stretching undergoes a downshift of 48 cm(-1) in passing from CCl(4) to the solid. DFT calculations provide a comprehensive interpretation of the evolution of the Raman spectra with solvent polarity.

The natural products cis-p-menthane-1,7-diol (cis-IV), cis-p-menth-8-ene-1,7-diol (cis-I) and cis-p-menthane-1,7,8-triol (cis-II) are obtained starting from the corresponding cis-cyanohydrins, cis-2 and cis-7, respectively, by chemical transformation of the cyano into the hydroxymethyl group. The key step of the synthesis is the very high cis-selectivity (> or = 96 %) of the MeHNL-catalyzed HCN addition to 4-alkylcyclohexanones. From 4-isopropylcyclohexanone (1) the cyanohydrin cis-2 and from 4-(1-methylvinyl)cyclohexanone (6) the cyanohydrin cis-7 result almost quantitatively. Regioselective hydroxylation of cis-I affords the triol cis-II. X-ray crystal structure determinations of the final products confirm their cis-configuration.

The influence of Trp128-substituted mutants of the hydroxynitrile lyase from Manihot esculenta (MeHNL) on the stereoselectivity of MeHNL-catalyzed HCN additions to aldehydes with stereogenic centers, which yield the corresponding cyanohydrins, is described. In rac-2-phenylpropionaldehyde (rac-1) reactions, wild-type (wtMeHNL) and all MeHNL Trp128 mutants are highly (S)-selective toward the (R) enantiomer of rac-1; this results exclusively in (2S,3R)-cyanohydrin ((2S,3R)-2) with > or =96 % de. The (S) enantiomer of rac-1, however, only reacts (S)-selectively with wtMeHNL to give (2S,3S)-2 with 80 % de, whereas with Trp128 mutants, (R) selectivity increases with decreasing size of the amino acids exchanged. The MeHNL W128A mutant is exclusively (R)-selective, resulting in (2R,3S)-2 with 86 % de. The reaction behavior of rac-phenylbutyraldehyde (rac-5) is comparable with rac-1, which also inverts the stereoselectivity from (S) to (R) when the enzyme is exchanged from wtMeHNL to the W128A mutant. Stereogenic centers not adjacent to the aldehyde group, as in 7 and 9, do not influence the stereoselectivity of MeHNL catalysis, and (S) selectivity is observed in all cases. Stereoselectivity and inversion of stereoselectivity of MeHNL Trp128 mutant-catalyzed cyanohydrin formation can be explained and rationalized with crystal-structure-based molecular modeling.

Organic thin film transistors (TFTs) are of interest for a variety of large-area electronic applications, such as displays, sensors and electronic barcodes. One of the key problems with existing organic TFTs is their large operating voltage, which often exceeds 20 V. This is due to poor capacitive coupling through relatively thick gate dielectric layers: these dielectrics are usually either inorganic oxides or nitrides, or insulating polymers, and are often thicker than 100 nm to minimize gate leakage currents. Here we demonstrate a manufacturing process for TFTs with a 2.5-nm-thick molecular self-assembled monolayer (SAM) gate dielectric and a high-mobility organic semiconductor (pentacene). These TFTs operate with supply voltages of less than 2 V, yet have gate currents that are lower than those of advanced silicon field-effect transistors with SiO2 dielectrics. These results should therefore increase the prospects of using organic TFTs in low-power applications (such as portable devices). Moreover, molecular SAMs may even be of interest for advanced silicon transistors where the continued reduction in dielectric thickness leads to ever greater gate leakage and power dissipation.

Several tryptophan128-substituted mutants of the hydroxynitrile lyase from Manihot esculenta (MeHNL) are constructed and applied in the MeHNL-catalyzed addition of HCN to various aromatic and aliphatic aldehydes as well as to methyl and ethyl ketones to yield the corresponding cyanohydrins. The mutants (especially MeHNL-W128A) are in most cases superior to the wild-type (wt) enzyme when diisopropyl ether is used as the solvent. Substitution of tryptophan128 by an alanine residue enlarges the entrance channel to the active site of MeHNL and thus facilitates access of sterically demanding substrates to the active site, as clearly demonstrated for aromatic aldehydes, especially 3-phenoxybenzaldehyde. These experimental results are in accordance with the X-ray crystal structure of MeHNL-W128A. Aliphatic aldehydes, surprisingly, do not demonstrate this reactivity dependence of mutants on substrate bulkiness. Comparative reactions of 3-phenoxybenzaldehyde with wtMeHNL and MeHNL-W128A in both aqueous citrate buffer and a two-phase system of water/methyl tert-butyl ether again reveal the superiority of the mutant enzyme: 3-phenoxybenzaldehyde was converted quantitatively into a cyanohydrin nearly independently of the amount of enzyme present, with a space-time yield of 57 g L(-1) h(-1).

The crystal structure of the hydroxynitrile lyase from Sorghum bicolor (SbHNL) in complex with the inhibitor benzoic acid has been determined at 2.3 A resolution and refined to a crystallographic R-factor of 16.5%. The SbHNL sequence places the enzyme in the alpha/beta hydrolase family where the active site nucleophile is predicted to be organized in a characteristic pentapeptide motif which is part of the active site strand-turn-helix motif. In SbHNL, however, a unique two-amino acid deletion is next to the putative active site Ser158, removing thereby the putative oxyanion hole-forming Tyr residue. The presented X-ray structure shows that the overall folding pattern of SbHNL is similar to that of the closely related wheat serine carboxypeptidase (CPD-WII); however, the deletion in SbHNL is forcing the putative active site residues away from the expected hydrolase binding site toward a small hydrophobic cleft, which also contains the inhibitor benzoic acid, defining thereby a completely different SbHNL active site architecture where the traditional view of a classic triad is not given any more. Rather, we propose a mechanism involving general base catalysis by the carboxy-terminal Trp270 carboxyl group and proton transfer toward the leaving nitrile group by an active site water molecule. The unexpected interactions of the inhibitor with the new SbHNL active site also reveal the structural basis for the enzyme's limited substrate specificity. The implications of this structure on the evolution of catalysis in the hydroxynitrile lyase superfamily are discussed.

The nitrilase AtNIT1 from Arabidopsis thaliana was overexpressed in Escherichia coli with an N-terminal His6 tag and purified by zinc chelate affinity chromatography in a single step almost to homogeneity in a 68% yield with a specific activity of 34.1 U.mg-1. The native enzyme (approximately 450 kDa) consists of 11-13 subunits (38 kDa). The temperature optimum was determined to be 35 degrees C and a pH optimum of 9 was found. Thus, recombinant AtNIT1 resembles in its properties the native enzyme and the nitrilase from Brassica napus. The stability of AtNIT1 could be significantly improved by the addition of dithiothreitol and EDTA. The substrate range of AtNIT1 differs considerably from those of bacterial nitrilases. Aliphatic nitriles are the most effective substrates, showing increasing rates of hydrolysis with increasing size of the residues, as demonstrated in the series butyronitrile, octanenitrile, phenylpropionitrile. In comparison with 3-indolylacetonitrile, the rate of hydrolysis of 3-phenylpropionitrile is increased by a factor of 330, and the Km value is reduced by a factor of 23. With the exception of fluoro, substituents in the alpha position to the nitrile function completely inhibit the hydrolysis.

Tryptophan 128 of hydroxynitrile lyase of Manihot esculenta (MeHNL) covers a significant part of a hydrophobic channel that gives access to the active site of the enzyme. This residue was therefore substituted in the mutant MeHNL-W128A by alanine to study its importance for the substrate specificity of the enzyme. Wild-type MeHNL and MeHNL-W128A showed comparable activity on the natural substrate acetone cyanohydrin (53 and 40 U/mg, respectively). However, the specific activities of MeHNL-W128A for the unnatural substrates mandelonitrile and 4-hydroxymandelonitrile are increased 9-fold and approximately 450-fold, respectively, compared with the wild-type MeHNL. The crystal structure of the MeHNL-W128A substrate-free form at 2.1 A resolution indicates that the W128A substitution has significantly enlarged the active-site channel entrance, and thereby explains the observed changes in substrate specificity for bulky substrates. Surprisingly, the MeHNL-W128A--4-hydroxybenzaldehyde complex structure at 2.1 A resolution shows the presence of two hydroxybenzaldehyde molecules in a sandwich type arrangement in the active site with an additional hydrogen bridge to the reacting center.

The structure and function of hydroxynitrile lyase from Manihot esculenta (MeHNL) have been analyzed by X-ray crystallography and site-directed mutagenesis. The crystal structure of the MeHNL-S80A mutant enzyme has been refined to an R-factor of 18.0% against diffraction data to 2.1-A resolution. The three-dimensional structure of the MeHNL-S80A-acetone cyanohydrin complex was determined at 2.2-A resolution and refined to an R-factor of 18.7%. Thr11 and Cys81 involved in substrate binding have been substituted by Ala in site-directed mutagenesis. The kinetic measurements of these mutant enzymes are presented. Combined with structural data, the results support a mechanism for cyanogenesis in which His236 as a general base abstracts a proton from Ser80, thereby allowing proton transfer from the hydroxyl group of acetone cyanohydrin to Ser80. The His236 imidazolium cation then facilitates the leaving of the nitrile group by proton donating.

Kinetic measurements of the acylation of toluene (2a) and p-xylene (2b), side-chain deuterated toluene (2a-d(3)), as well as perdeuterated toluene (2a-d(8)) and p-xylene (2b-d(10)) with the aroyl triflate 1 in 1,2-dichloroethane reveal a strong dependence of the isotope effect on reaction conditions. In the presence of trifluoromethanesulfonic acid (HOTf), the second-order rate constants k(H)/k(D) observed are in the order of 1.75-1.94, whereas in the presence of 2,4,6-tri-tert-butylpyridine (4) rate constants k(H)/k(D) of 1.14-1.25 are found. The primary kinetic isotope effects observed correlate with the ortho/para ratio of the acylation of toluene. In the presence of 4 a relatively high percentage ( approximately 30%) of ortho product is obtained, whereas under acidic conditions the ratio is only 10%. The correlation between isotope effects and isomer distributions is obviously due to the rate of deprotonation of the corresponding sigma-complex intermediates. Assuming a bent structure for sigma-complexes, the conformation giving deprotonation is preferred in the para sigma-complex in comparison with ortho complex.

The crystal structures of hydroxynitrile lyase from Manihot esculenta (MeHNL) complexed with the native substrate acetone and substrate analogue chloroacetone have been determined and refined at 2.2 A resolution. The substrates are positioned in the active site by hydrogen-bond interactions of the carbonyl O atom with Thr11 OG, Ser80 OG and, to a lesser extent, Cys81 SG. These studies support a mechanism for cyanogenesis as well as for the stereospecific MeHNL-catalyzed formation of (S)-cyanohydrins, which closely resembles the base-catalyzed chemical reaction of HCN with carbonyl compounds.

(R)- as well as (S)-cyanohydrins are now easily available as a result of the excellent accessibility, the relatively high stability and the easy handling of hydroxynitrile lyases (HNLs). The optimization of reaction conditions (solvent, temperature, and using site-directed mutagenesis, etc.) has enabled HNL-catalyzed preparations of optically active cyanohydrins on a technical scale. The enantioselectivity of chiral metal-complex-catalyzed additions of trimethylsilyl cyanide to aldehydes has been improved, but is, by far, not yet competitive with the HNL-catalyzed reactions.

(S)-Ketone cyanohydrins (S)-2 are accessible by enantioselective HCN addition to ketones 1 by using hydroxynitrile lyase from Manihot esculenta ((S)-MeHNL) as a biocatalyst. Acylation of (S)-2 gave the corresponding (S)-acyloxynitriles (S)-3, which can be cyclized by LHMDS to give 5,5-disubstituted (S)-4-amino-2(5H)-furanones (S)-4 and (S)-5. Different substituents (H. Me, OBn, OH) in the 3-position of the furanones were introduced by selecting the appropriate acylating agent, which in the case of benzyloxyacetyl chloride led to the novel structure type of 4-amino-3-hydroxyfuranones (S)-5. For the synthesis of 5,5-disubstituted (S)-tetronic acids (S)-8, ketone cyanohydrins (S)-2 were first transformed into the corresponding 2-hydroxy esters (S)-6. Acylation of (S)-6 gave 2-acyloxy esters (S)-7, which, by treatment with LHMDS or LDA, afforded tetronic acids (S)-8 in high yields and enantiomeric excesses. By debenzylation of benzyloxy acetoxy derivatives (S)-8e,f, the new vitamin C analogues (S)-9a,b were generated. All the described tetronic acid and aminofuranone derivatives were obtained in good chemical yields and without racemization with respect to the starting cyanohydrins (S)-2. In many cases the enantiomeric purity could be enriched by simple recrystallization (e.g. (S)-4a from 69% ee to > 99% ee).

According to Jerne's network hypothesis, the binding site of an anti-idiotypic antibody also represents the internal image of an epitope present on a foreign, or even a self antigen. In recent years, antigen mimicry has been defined at the molecular level for some xeno-antigens. However, until now there has been no demonstration of structural mimicry between a human anti-idiotypic antibody and a self structure. To address this question, we used human IgE as the self structure and a well-defined anti-human IgE mAb (BSW17). We describe the isolation of two anti- idiotypic antibodies specific for the anti-IgE antibody BSW17 from a non-immune human Fab phage display library. Interestingly, these two anti-idiotypic antibodies mimic the same molecular surface region as a previously described IgE peptide mimotope isolated by panning on BSW17, but they cover a much larger epitope on the IgE molecule. Accordingly, immunisation of rabbits with the two anti-idiotypic antibodies induced high-affinity antibodies with the same characteristics as BSW17. Thus, our data demonstrate that it is possible to isolate anti-idiotypic antibodies derived from the human genome without the need for hyperimmunization, and confirm Jerne's hypothesis that both foreign antigens and self structures can be mimicked by our own immunoglobulins., (Copyright 2000 Academic Press.)

Hydroxynitrile lyase from M. esculenta (cassava) was crystallized in two different crystal forms by the hanging-drop vapour-diffusion method. Crystals of form I were obtained from a mixture of polyethylene glycol 8000 and 2-methyl-2,4-pentanediol, and belong to the tetragonal space group P41212 or its enantiomorph P43212, with unit-cell parameters a = b = 105.9, c = 188.9 A and with two molecules in the asymmetric unit. These crystals diffract to 2.9 A with conventional X-ray sources and beyond 2.1 A resolution with synchrotron radiation. The crystals are relatively sensitive to radiation damage and conditions for flash-cooling the crystals have been established. A complete native data set has been collected up to 2.2 A resolution. Crystal form II has been obtained at pH 5.6 using lithium sulfate as a precipitant. The crystals apparently belong to the orthorhombic space group P21212, with unit-cell parameters a = 117.52, b = 127.09 and c = 78.08 A, have two molecules in the asymmetric unit and diffract to beyond 2.0 A resolution. A complete native data set has been collected to 2.2 A resolution.

Direct lateral patterning in the formation of self-assembled monolayers (SAMs) on silicon was achieved by the photoinduced reaction of aldehydes with Si(111)-H surfaces by using the usual masking techniques (see the schematic illustration; on the right-hand side is a microscopy image of a patterned SAM formed from octadecanal)., (© 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

A panel of monoclonal antibodies (8H10/D11, 6F9/H8, 6F9/G9, 5F2/F8/H11, 5F2/F8/G10, 8A4/G12/F9, and 8H10/F12) was raised in mice against the recombinant 20-kDa extracellular part of the alpha-chain of the human IgE high affinity receptors (ecFc epsilon RIalpha) produced in insect cells. The antibodies secreted by hybridomas were selected for specific binding to ecFc epsilon RIalpha, by enzyme-linked immunosorbent assay (ELISA). The selected clones were further characterized in surface plasmon resonance (SPR) experiments with ecFc epsilon RIalpha covalently immobilized on the surface of a sensor chip. The generated hybridomas can be divided into three groups. Hybridoma supernatants 8A4/G12/F9 and 8H10/F12 inhibited binding of human IgE to immobilized ecFc epsilon RIalpha in SPR (Group 1). Isotyping revealed that 8A4/G12/F9 and 8H10/F12 were of the IgE/kappa type. Antibodies present in the remaining supernatants were noninhibitory and bound to ecFc epsilon RIalpha in ELISA with intensities comparable to each other. Isotype analysis of antibodies secreted by these hybridomas showed that the antibodies 6F9/H8, 6F9/G9, 5F2/F8/H11, 5F2/F8/G10, and 8H10/D11 were IgG1/kappa. The hybridoma supernatants were purified via protein A chromatography. In a SPR experiment, ecFc epsilon RIalpha, displayed by immobilized human IgE, was still recognized by 6F9/H8 and 6F9/G9 (Group 2) as expected for noninhibitory antibodies. Surprisingly, 8H10/D11, 5F2/F8/H11, and 5F2/F8/G10 (Group 3) did not bind to this complex although they do not inhibit the binding of human IgE to ecFc epsilon RIalpha. All purified monoclonal antibodies gave positive signals in Western blotting.