Tunnel Back Research Articles

Addressing discontinuous root-finding for subsequent differentiability in machine learning, inverse problems, and control

There are many physical processes that have inherent discontinuities in their mathematical formulations. This paper is motivated by the specific case of collisions between two rigid or deformable bodies and the intrinsic nature of that discontinuity. The impulse response to a collision is discontinuous with the lack of any response when no collision occurs, which causes difficulties for numerical approaches that require differentiability which are typical in machine learning, inverse problems, and control. We theoretically and numerically demonstrate that the derivative of the collision time with respect to the parameters becomes infinite as one approaches the barrier separating colliding from not colliding, and use lifting to complexify the solution space so that solutions on the other side of the barrier are directly attainable as precise values. Subsequently, we mollify the barrier posed by the unbounded derivatives, so that one can tunnel back and forth in a smooth and reliable fashion facilitating the use of standard numerical approaches. Moreover, we illustrate that standard approaches fail in numerous ways mostly due to a lack of understanding of the mathematical nature of the problem (e.g. typical backpropagation utilizes many rules of differentiation, but ignores L'Hopital's rule).

A Chemical Pump that Generates High‐Pressure Gas by Transmitting Liquid Fuel against Pressure Gradient

A pneumatic soft robot can be made autonomous by carrying a liquid chemical fuel. In the existing design, to transmit the fuel, the pressure of the fuel tank must exceed that of the actuator. Consequently, the fuel tank must be sufficiently stiff, which hardens the robot. Herein, inspired by pit membranes in trees, a chemical pump is developed, which is consisting of a nanoporous membrane between the fuel tank and the actuator, and coated with a catalyst on the side of the actuator. The fuel in the fuel tank migrates across the membrane and, on meeting the catalyst, decomposes into a pressurized gas and inflates the actuator. The chemical pump is driven by the free energy of reaction, against the difference in pressure. The pores in the membrane are large enough for the fuel molecules to migrate through, but small enough to block the pressurized gas to tunnel back. In a demonstration, the fuel tank has ambient pressure, and the actuator has a pressure of 350 kPa, comparable to the pressure in a car tire. The chemical pump enables pneumatic robots to be autonomous, powerful, and soft.

Tunnel Back Analysis Based on Differential Evolution Using Stress and Displacement

The stability of tunnels has mainly been evaluated based on displacement. Because displacement due to the excavation process is significant, back analysis of the structure and ground can be performed easily. Recently, the length of a segment‐lined tunnel driven by the mechanized tunneling method is increasing. Because the internal displacement of a segment‐lined tunnel is trivial, it is difficult to analyze the stability of segment‐lined tunnels using the conventional method. This paper proposes a back analysis method using stress and displacement information for a segment‐lined tunnel. A differential evolution algorithm was adopted for tunnel back analysis. Back analysis based on the differential evolution algorithm using stress and displacement was established and performed using the finite difference code, FLAC3D, and built‐in FISH language. Detailed flowcharts of back analysis based on DEA using both monitored displacement stresses were also suggested. As a preliminary study, the target variables of the back analysis adopted in this study were the elastic modulus, cohesion, and friction angle of the ground. The back analysis based on the monitored displacement is useful when the displacement is significant due to excavation. However, the conventional displacement‐based back analysis is unsuitable for a segment‐lined tunnel after construction because of its trivial internal displacement since the average error is greater than 32% and the evolutionary calculation is finalized due to the maximum iteration criteria. The average error obtained from the proposed back analysis algorithm using both stress and displacement ranged within approximately 6–8%. This also confirms that the proposed back analysis algorithm is suitable for a segment‐lined tunnel.

Threshold-voltage shift model based on electron tunneling under positive gate bias stress for amorphous InGaZnO thin-film transistors

An analytical threshold-voltage (Vth) shift model of amorphous InGaZnO thin-film transistors (a-IGZO TFTs) under positive gate bias stress (PGBS) is reported in this paper. It is demonstrated that electrons in active layers of a-IGZO TFTs can tunnel into gate insulators when PGBS is applied, and a portion of the tunneled electrons would tunnel back. The transfer distance of the tunneled electrons and the time-dependent electron distribution in gate insulators are analyzed with the back-tunneling effect taken into consideration. Finally the Vth shift under PGBS is predicted and the influences of gate voltage and stress time are discussed. The calculated Vth shift under PGBS shows good consistency with the reported experimental data.

Quantum Nuclear Dynamics of Protons within Layered Hydroxides at High Pressure

Studies of the structure of hydroxides under pressure using neutron diffraction reveal that the high concentration of hydrogen is distributed in a disordered network. The disorder in the hydrogen-bond network and possible phase transitions are reported to occur at pressures within the range accessible to experiments for layered calcium hydroxides, which are considered to be exemplary prototype materials. In this study, the static and dynamical properties of these layered hydroxides are investigated using a quantum approach describing nuclear motion, shown herein to be required particularly when studying diffusion processes involving light hydrogen atoms. The effect of high-pressure on the disordered hydrogen-bond network shows that the protons tunnel back and forth across the barriers between three potential minima around the oxygen atoms. At higher pressures the structure has quasi two-dimensional layers of hydrogen atoms, such that at low temperatures this causes the barrier crossing of the hydrogen to be significantly rarefied. Furthermore, for moderate values of both temperature and pressure this process occurs less often than the usual mechanism of proton transport via vacancies, limiting global proton diffusion within layers at high pressure.

Flash Memory Featuring Low-Voltage Operation by Crystalline ZrTiO4 Charge-Trapping Layer

Crystalline ZrTiO4 (ZTO) in orthorhombic phase with different plasma treatments was explored as the charge-trapping layer for low-voltage operation flash memory. For ZTO without any plasma treatment, even with a high k value of 45.2, it almost cannot store charges due the oxygen vacancies-induced shallow-level traps that make charges easy to tunnel back to Si substrate. With CF4 plasma treatment, charge storage is still not improved even though incorporated F atoms could introduce additional traps since the F atoms disappear during the subsequent thermal annealing. On the contrary, nevertheless the k value degrades to 40.8, N2O plasma-treated ZTO shows promising performance in terms of 5-V hysteresis memory window by ±7-V sweeping voltage, 2.8-V flatband voltage shift by programming at +7 V for 100 μs, negligible memory window degradation with 105 program/erase cycles and 81.8% charge retention after 104 sec at 125 °C. These desirable characteristics are ascribed not only to passivation of oxygen vacancies-related shallow-level traps but to introduction of a large amount of deep-level bulk charge traps which have been proven by confirming thermally excited process as the charge loss mechanism and identifying traps located at energy level beneath ZTO conduction band by 0.84 eV~1.03 eV.

An ARC less InGaP/GaAs DJ solar cell with hetero tunnel junction

Multi junction solar cell has not achieved an optimum performance yet. To acquire more conversion efficiency research on multi junction solar cell are in progress. In this work we have proposed a dual junction solar cell with conversion efficiency of 43.603%. Mainly the focus is given on the tunnel diode, window layer and back surface field (BSF) layer of the cell, as all of them plays important role on the cell performance. Here we have designed a hetero InGaP/GaAs tunnel diode which makes tunnel diode more transparent to the bottom cell as well as reduces the recombination at the interfaces. The thickness of the window and BSF layer are optimized to achieve higher conversion efficiency. The simulation is carried out using Silvaco ATLAS TCAD under 1000 sun of AM1.5G spectrum. Different performance parameters of the cell like short circuit current density (Jsc), open circuit voltage (Voc), external quantum efficiency (EQE), fill factor (FF), conversion efficiency (η), spectral response and photogeneration rate of the cell are examined and compared with previously reported literatures. For the proposed model a Voc of 2.7043 V, Jsc of 1898.52 mA/cm2, FF of 88.88% and η of 43.6% are obtained.

Design and evaluation of ARC less InGaP/GaAs DJ solar cell with InGaP tunnel junction and optimized double top BSF layer

The presence and performance of the tunnel junction layer and back surface field (BSF) layers is the chief reason behind the high efficiency of the multi-junction solar cells. In this work, the focus is on the selection of a suitable material for the tunnel junction along with introducing a new top BSF layer. The simulation work is carried out in ATLAS TCAD. The various performance parameters like open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF) and efficiency (η) are extracted from the proposed solar cell model and are compared with published results to ascertain the accuracy of the present work. Other parameters like the photogeneration rate, spectral response, potential developed, electric field are also determined. I–V curve and the power curve are also plotted for the proposed model. For this proposed structure VOC=2.668V, JSC=18.2mA/cm2, FF=88.29% and η=40.879% are obtained for 1000 suns illuminated under standard AM1.5G spectrum. The obtained outputs and the modeling steps are elaborately explained.

Charge Trapping Memory with 2.85-Nm Si-Nanoparticles Embedded in HfO2

Innovative means to reduce the operating voltage and increase the stored charge density in current non-volatile memory devices are imperative [1-5]. In this work, 2.85-nm Si nanoparticles (Si-NPs) embedded in an ultrathin HfO2 layer are investigated for charge storage in low-cost non-volatile charge trapping memory devices. The memory hysteresis at different gate voltages, the stored charge, and the energy band diagram of the memory structure are analyzed. The memory cells are fabricated on an n+-type (111) (Antimony doped, 15-20 mΩ-cm) Si wafer. 5-nm-thick tunnel oxide Al2O3 is deposited at 250°C in Cambridge Nanotech Savannah-100 atomic layer deposition (ALD) system. Then, 1-nm-thick HfO2 is deposited by Plasma Assisted ALD at 195°C in an Oxford FlexAL system. Next, 2.85-nm Si-NPs are spin coated on the sample [6]. Again, a 1-nm-thick HfO2 is deposited by plasma assisted ALD at 195°C. Finally, an 8-nm-thick Al2O3 blocking oxide is deposited by ALD at 250°C. A 400-nm-thick Al layer for the gate contact is e-beam evaporated using a shadow mask with 10 μm feature size which eliminated the need for lithography steps. A cross-sectional illustration of the fabricated memory device is depicted in Fig. 1. The fabricated memory devices are electrically characterized by measuring the high frequency (1 MHz) C-Vgate characteristics of the programmed and erased states. Using the Agilent B1505A Semiconductor Device Parameter Analyzer, the memory cells gate voltage was first swept from -6 V forward to 6 V then backwards. A 1.8 V threshold voltage (Vt) shift is observed. The C-V measurements are repeated at a gate sweeping voltage of 8/-8 V and both erased and programmed states shifted outwards as shown in Fig. 2 resulting in a 4.5 V memory window. This indicates that the charge trapping layer is storing mixed charges: electrons and holes, however, more charging is due to holes revealed by the greater shift of the erased state in the negative direction as shown in Fig. 2. Moreover, the Vt shift is measured at different gate sweeping voltages as sown in Fig. 3 and the charge trapping density in the Si-NPs is calculated [3] and found to be 2.32 ×1013 cm-3. The analysis of the energy band diagram shows that the conduction band offset between Si and tunnel oxide is smaller than the valence band offset (ΔEC = 2.44 eV < ΔEV = 3.24 eV), thus the electrons tunneling probability is expected to be higher. However, the conduction band offset between the 2.85-nm Si-NPs [7] and tunnel oxide is much smaller than the valence band offset (ΔEC = 1.29 eV << ΔEV = 3.77 eV). This means that stored electrons can tunnel back to the Si channel much easier than holes. This confirms the observed larger charging due to holes in Fig. 2. Moreover, the addition of the high-dielectric constant (қ=20) HfO2 layer is expected to reduce the leakage of stored charges. Finally, the fabrication of such memory structure is compatible with existing semiconductor processing thus has potential on low-cost integrated nanoscale memory applications. Acknowledgment: This work was supported by ATIC, and TUBITAK Grants 109E044, 112M004, 112E052 and 113M815.

Underground Excavation Behaviour of the Queenston Formation: Tunnel Back Analysis for Application to Shaft Damage Dimension Prediction

The Niagara Tunnel Project (NTP) is a 10.1 km long water-diversion tunnel in Niagara Falls, Ontario, which was excavated by a 7.2 m radius tunnel boring machine. Approximately half the tunnel length was excavated through the Queenston Formation, which locally is a shale to mudstone. Typical overbreak depths ranged between 2 and 4 m with a maximum of 6 m observed. Three modelling approaches were used to back analyse the brittle failure process at the NTP: damage initiation and spalling limit, laminated anisotropy modelling, and ubiquitous joint approaches. Analyses were conducted for three tunnel chainages: 3 + 000, 3 + 250, and 3 + 500 m because the overbreak depth increased from 2 to 4 m. All approaches produced similar geometries to those measured. The laminated anisotropy modelling approach was able to produced chord closures closest to those measured, using a joint normal to shear stiffness ratio between 1 and 2. This understanding was applied to a shaft excavation model in the Queenston Formation at the proposed Deep Geological Repository (DGR) site for low and intermediate level nuclear waste storage in Canada. The maximum damage depth was 1.9 m; with an average of 1.0 m. Important differences are discussed between the tunnel and shaft orientation with respect to bedding. The models show that the observed normalized depth of failure at the NTP would over-predict the depth of damage expected in the Queenston Formation at the DGR.

Temperature Effect on Memory Functions of the nc-CdSe Embedded ZrHfO High-k MOS Device

The nanocrystals embedded high-k dielectric can replace the floating-gate dielectric for the nonvolatile memory (NVM) device for advantages of low leakage current and high reliability [1]. The doped metal oxide high-k film, e.g., Zr-doped HfO2 (ZrHfO), has good bulk and interface properties for the gate dielectric application [2]. The nanocrystalline cadmium selenide (nc-CdSe) embedded ZrHfO MOS has a large charge-trapping density with a long retention time [3]. Since in the densely packed circuit the temperature can be much higher than the room temperature, it is imperative to understand the device’s charge trapping and detrapping mechanisms at a raised temperature [4]. The ZrHfO/nc-CdSe/ZrHfO gate dielectric stack was sputter deposited in one pumpdown on the dilute HF cleaned p-type Si (100) wafer. The ZrHfO films were deposited from the ZrHf target in the Ar/O2 atmosphere, i.e., 2 min for the tunnel oxide and 10 min for the control oxide layers. The CdSe film was deposited from the CdSe target in pure Ar at 5 mTorr and 60 W for 3 min. The detailed device fabrication process can be found in ref. 3. Figure 1 shows J-V curves of the nc-CdSe embedded sample measured with the gate voltage Vg swept from -6 V to +6 V and then back to -6 V at 20ºC, 70ºC, and 120ºC, separately. In the negative Vg range, each curve has a peak A near Vg = 0 V, which is due to the quick release of the shallow-trapped holes. When the temperature is increased, those trapped charges are easily released because of the increase of the thermal energy [5]. There is another peak B in the 20ºC curve, which is due to the Coulomb blockade effect. The size of the peak becomes negligible small at 70ºC and 120ºC because of the reduction of the Coulomb blockade effect [6]. Figure 2 shows the C-V curves of the nc-CdSe embedded sample measured at two different directions, i.e., from -6 V to +6 V or from +6 V to -6 V. Compared with the fresh sample measured from -2 V to +1 V, the C-V curves with Vg swept from -6 V to + 6V shifts toward the negative Vg direction because of the trap of holes from the p-type Si. The magnitude of the shift increases with the increase of the temperature because more free holes are formed in the substrate and injected to the high-k stack [5]. On the other hand, the curve with Vg swept from +6 V to - 6V shifts to the positive Vg direction of the fresh sample because of the trap of electrons. The magnitude of the shift decreases with the increase of the temperature. According to the band diagram in ref. 3, the valence band offset is much larger than the conduction band offset between Si and HfSiOx. At the high temperature, the electrons can be transferred through the high-k stack without being trapped to the nc-CdSe site. This is in consistent with the result of Fig. 1 where the leakage current increases with the temperature. The temperature effect is also affected by the measurement frequency. For example, the C-V curves of the control and the nc-CdSe embedded samples were measured at different frequencies and temperatures. The control sample shows negligible frequency dispersion at 20oC. But the nc-CdSe embedded sample shows the obvious frequency dispersion phenomenon. The C-V curves shifted toward the positive Vg direction when the measurement frequency was decreased from 1 MHz to 100 kHz. This is because the shallow-trapped charges, e.g., at the nc-CdSe/ZrHfO interface, respond slowly to the frequency [3]. When the temperature is increased, the amount of charges increases. More holes can tunnel back to the Si substrate at the high temperature. A should is observed in the 100 kHz curve near the flat-band voltage at 120ºC. In addition, the C-V curve slope becomes more flat with the increase of the temperature from 20ºC to 120ºC due to the increase of interface density of states.Authors acknowledge the support of this work through the NSF CMMI 0926379 project. S. Zhang thanks Mr. Chi-Chou Lin for help in sample preparation and technical discussions.[1] C.-H. Lin et al. J AP., 110, 024101 (2011).[2] J. Lu et al. APL., 87,232906 (2005).[3] C.-C. Lin et a. JAP., 115, 084113 (2014).[4] C. H. Yang et al. MRS Symp. Proc., 1071, F02 (2008).[5] C.-H. Yang et al. ESL., 14, H50 (2011).[6] C.-C. Lin et al. ECS JSSST., 2, Q16 (2013).

Instability of an emergent universe

Oscillating solutions to the effective equations of Loop Quantum Cosmology have been suggested for the role of an `eternal seed', providing a possible starting point for the emergent universe scenario. We investigate the stability of a particular model, sourced by a homogeneous massless scalar field and a negative cosmological constant, with respect to small perturbations and to quantum collapse. We find that the model has perturbatively stable and unstable solutions, with both types of solutions occupying significant regions of the parameter space. All solutions are unstable with respect to collapse by quantum tunneling to zero size. We discuss the possibility that the state resulting from the collapse is non-singular, so it may tunnel back to the oscillating regime. We argue that the universe is then likely to evolve to states of very large size with large particle occupation numbers.

Psychopathologie du jeu multi-joueurs en ligne

ObjectivesOnline multiplayer videogames have become one of the most addictive activities on the Internet. However, overconsumption of online videogames should be differentiated of Internet addiction since players do not report to experience to be on the Internet when they are playing. MethodsThe present article provides a comprehensive review of data on online multiplayer videogames overconsumption. This review highlights motivational factors of overconsumers and available therapeutic strategies will be described. ResultsOverconsumption of online videogames is considered as a behavioural addiction or a compulsive-impulsive disorder. Most of the articles highlight four criteria for this disorder: (1) excessive use, often associated with a loss of sense of time or a neglect of basic drives, (2) withdrawal, including feelings of anger, tension, and/or depression when the computer is inaccessible, (3) tolerance, including the need for better computer equipment, more software, or more hours of use, and (4) negative repercussions, including arguments, lying, poor achievement, social isolation, and fatigue. Online multiplayer videogames are endlessly addictive, with daily consumption commonly lasting more than six hours. These games are easily accessible, since they only require an Internet access and demonstration trials are free to download. However, overconsumption of these videogames leads quickly to social withdrawal, academic failure, and disinvestment in daily-life activities. Males play more often than women. Teenagers and young adults are principal overconsumers of online multiplayer videogames and of the Internet. Parental control influences overconsumption since parental control is negatively correlated with Internet consumption in non-depressed adolescents. Comorbidities of abusive consumption are mood disorders, depressive symptoms and suicidal thoughts, anxiety disorders (generalized anxiety disorder and social phobia), alexithymia, attention deficit hyperactivity disorder and personality disorders (avoidant, borderline and obsessive-compulsive). Overuse is also associated with cannabis and alcohol consumptions, sleep deprivation, compulsive eating disorder, carpal tunnel syndrome, ocular dryness, back- and headaches. Individuals with addictive behaviours for Internet and online videogames addiction tend to attribute the causes of events to the chance, they anticipate negatives consequences of their acts, demonstrate negativism, tendency to catastrophization, shame, low self-esteem and self-confidence. Three major desires lead to overconsumption in adolescents: the achievement of success, the creation of social relationships, and the immersion in an environment that differs from reality. French psychiatrists recommend treating overuse with a combination of pharmacologic and psychotherapeutic approaches. Among psychotherapeutic treatment, cognitive and behavioural therapies have demonstrated their efficacy with the disorder. Unfortunately, the literature does not provide information on other useful therapies. ConclusionsGiven the growing frequency of overconsumption of online videogames and of the Internet, motivations of players and comorbidities of the disorder must be known by the clinician. They are clues to orientate the therapeutic approaches.

인공신경망 기법과 굴진면 관찰자료를 활용한 터널 역해석 연구

터널 설계 시 사용되는 지반물성치는 한정적인 조사 및 시험을 통해 산정되기 때문에 불확실성을 내포한다. 본 연구에서는 최적의 지반물성치를 찾기 위해 터널의 굴진면 관찰자료와 계측자료를 활용하여 인공신경망을 이용한 역해석을 수행하였다. 우선 굴진면 관찰자료를 이용하여 연구대상 터널의 암반등급이 선정되었다. 기존연구에 대한 문헌고찰을 통해서 암반등급별로 지반물성치의 가능한 범위를 지정하여 보다 정확한 학습자료 구축을 위해 활용되었다. 또한 최적의 학습모델을 찾기 위해 은닉층 수와 각 은닉층의 노드 수를 기존연구보다 세분하여 변화시켜가며 매개변수 연구를 수행하였다. 연구결과, 기존 연구와 비교했을 때, 보다 정확한 지반물성치를 얻을 수 있었다. 따라서 계측자료 뿐만 아니라 굴진면 관찰자료를 인공신경망을 이용한 역해석에 활용하면 결과의 정확성을 높일 수 있음을 확인하였다. 향후 본 연구에서 제시된 방법론을 사용하여 지반물성치를 보다 정확하게 추정할 수 있을 것으로 기대된다. Considerable uncertainties are included in ground properties used for tunnel designs due to the limited investigation and tests. In this study, a back analysis was performed to find optimal ground properties based on artificial neural network using both face mapping data and convergence measurement data. First of all, the rock class of a study tunnel is determined from face mapping data. Then the possible ranges of ground properties were selected for each rock class through a literature review on the previous studies and utilized to establish more precise learning data. To find an optimal training model, a sensitivity analysis was also conducted by varying the number of hidden layers and the number of nodes more minutely than the previous study. As a result of this study, more accurate ground properties could be obtained. Therefore it was confirmed that the accuracy of the results could be increased by making use of not only convergence measurement data but also face mapping data in tunnel back analyses using artificial neural network. In future, it is expected that the methodology suggested in this study can be used to estimate ground properties more precisely.

A novel technique of permanent self-catheterizable feeding jejunostomy

Long-term/permanent jejunal feeding in children and adults is prone to significant complications, such as leakage, skin excoriation, and difficulty in reinsertion after dislodgement of the jejunostomy tube. Our innovative jejunostomy technique uses a pedicle segment of jejunum, which is retubularized using the principle of Monti. The jejunal segment is reinserted through a submucosal tunnel back into the jejunum. The other end is brought out onto the abdominal wall. The technique achieves a continent catheterizable jejunal stoma for enteral feeding.

Relationship Between the Heat Flow and the Current through a Superconducting Tunnel Junction

Abstract Nonequilibrium quasiparticles injected into the biased film of a superconducting tunnel junction (STJ) give rise to the electrical current across the insulating barrier. Each quasiparticle in superconductor is a quantum superposition of electron-like and hole-like excitations. This duality nature of quasiparticle leads to the process of quasiparticle multitunneling. Quasiparticle begins tunnel back and forth across the insulating barrier until it will be out of the game. After each tunneling from the biased film, quasiparticle loses its energy by emission of phonons until it reaches the gap energy. Because of the multitunneling, one quasiparticle can deposit the excess of its energy more than once. In this work, the theory of branching cascade processes is applied to the processes of the heat and the charge flow caused by the process of quasiparticle multitunneling. The relationship between the heat flow and the current through a superconducting tunnel junction is derived. It was shown that energetic X-rays at high counting rates may cause additional broadening of the spectral lines in STJ detectors due to temperature fluctuations through dependence of the gap energy on the temperature.

Mesoscopic phenomena in Au nanocrystal floating gate memory structure

A resonant tunneling process is demonstrated in the HfAlO/Au nanocrystals/HfAlO trilayer nonvolatile memory (NVM) structure on Si, where the electrons tunnel back and forth to the Au nanocrystals due to the various mesoscopic behaviors. The electron tunneling behavior in this trilayer structure exhibits dissimilar resemblance to those in double-barrier tunnel junctions taking into account of the correlation of Coulomb blockade effect. The observed specific tunneling process is beneficial in studying the interplays of various mesoscopic physics and application of single electron devices into NVM.

Atom-pair tunneling and quantum phase transition in the strong-interaction regime

We propose a Hamiltonian of ultracold spinless atom in optical lattices including the two-body interaction of nearest neighbors, which reduces to the Bose-Hubbard model in weak-interaction limit. An atom-pair hopping term appearing in the Hamiltonian explains naturally the recent experimental observation of correlated tunneling in a double-well trap with strong atom-atom interactions and moreover leads to a dynamic process of atom-pair tunneling where strongly interacting atoms can tunnel back and forth as a fragmented pair. Finally a dynamics of oscillations induced by the atom-pair tunneling is found in the strong interaction regime, where the Bose-Hubbard model gives rise to the insulator state with fixed time-averaged value of atom-occupation number only. Quantum phase transitions between two quantum phases characterized by degenerate and nondegenerate ground states are shown to be coinciding with the Landau second-order phase-transition theory. In the system of finite atom number the degeneracy of ground states can be removed by quantum tunneling for the even number of atoms but not for the odd number.

Viscosity-dependent Relaxation Significantly Modulates the Kinetics of CO Recombination in the Truncated Hemoglobin TrHbN from Mycobacterium tuberculosis

Kinetic traces were generated for the nanosecond and slower rebinding of photodissociated CO to trHbN in solution and in porous sol-gel matrices as a function of viscosity, conformation, and mutation. TrHbN is one of the two truncated hemoglobins from Mycobacterium tuberculosis. The kinetic traces were analyzed in terms of three distinct phases. These three phases are ascribed to rebinding: (i) from the distal heme pocket, (ii) from the adjacent apolar tunnel prior to conformational relaxation, and (iii) from the apolar tunnel subsequent to conformational relaxation. The fractional content of each of these phases was shown to be a function of the viscosity and, in the case of the sol-gel-encapsulated samples, sample preparation history. The observed kinetic patterns support a model consisting of the following elements: (i) the viscosity and conformation-sensitive dynamics of the Tyr(B10) side chain facilitate diffusion of the dissociated ligand from the distal heme pocket into the adjacent tunnel; (ii) the distal heme pocket architecture determines ligand access from the tunnel back to the heme iron; (iii) the distal heme pocket architecture is governed by a ligand-dependent hydrogen bonding network that limits the range of accessible side chain positions; and (iv) the apolar tunnel linking the heme site to the solvent biases the competition between water and ligand for occupancy of the vacated polar distal heme pocket greatly toward the nonpolar ligand. Implications of these finding with respect to biological function are discussed.

SWITCHING OXIDE TRAPS

Positive oxide trapped charge is one of the main factors determining the radiation response of a CMOS device. The most widely accepted model for oxide-trapped charge is the dipole model, originally proposed by Lelis et al. The annealing of radiation-induced positive trapped charge proceeds (usually) via the tunneling of electrons, which form metastable dipoles, compensating the trapped positive charge without removing it. Under appropriate bias, these compensating electrons can tunnel back to the Si substrate, restoring the trapped positive charge. The experimental work leading to the development of this model is summarized. By now there is a large body of experimental and theoretical work by others, confirming and extending the original model. In particular, the relevance of the model to some electron trapping studies has been shown, and its application to the larger topic of oxide reliability is discussed.