We implemented the well-known Ising model in one dimension as a computer program and simulated its behavior with four algorithms: (i) the seminal Metropolis algorithm; (ii) the microcanonical algorithm described by Creutz in 1983; (iii) a variation on Creutz’s time-reversible algorithm allowing for bonds between spins to change dynamically; and (iv) a combination of the latter two algorithms in a manner reflecting the different timescales on which these two processes occur (“freezing” the bonds in place for part of the simulation). All variations on Creutz’s algorithm were symmetrical in time, and thus reversible. The first three algorithms all favored low-energy states of the spin lattice and generated the Boltzmann energy distribution after reaching thermal equilibrium, as expected, while the last algorithm broke from the Boltzmann distribution while the bonds were “frozen.” The interpretation of this result as a net increase to the system’s total entropy is consistent with the second law of thermodynamics, which leads to the relationship between maximum entropy and the Boltzmann distribution.
The photodissociation of 1-bromobutane is explored using pump-probe spectroscopy and time-of-flight mass spectrometry. Fragments of bromobutane are constructed computationally and theoretical energies are calculated using Gaussian 16 software. It is determined that the dissociation of bromine from the parent molecule is the most observed fragmentation pathway arising from the excitation of the ground state parent molecule to a dissociative A state using two 400 nm, 3.1 eV pump photons. The dissociation energy of this pathway is 2.91 eV, leaving 3.3 eV of energy that is redistributed into the product fragments as vibrational energy. C4H9 has the highest relative intensity in the mass spectrum with a relative intensity of 1.00. It is followed by C2H5 and C2H4 at relative intensities of 0.73 and 0.29 respectively. Because of the negative correlation between C4H9 and these two fragments at positive time delays, it is concluded that most of these smaller molecules are formed from the further dissociation of the fragment C4H9 rather than any alternative pathways from the parent molecule. Thermodynamic analysis of these pathways has displayed the power of thermodynamic prediction as well as its limitations as it fails to consider kinetic limitations in dissociation reactions.
Startups in the paper manufacturing industry are few and far between. Agrix paper takes a step towards innovating the traditional mass-scale paper making process and introduces non-wood fiber sourcing into the papermaking space. Using a hemp fiber base, Agrix Paper hopes to develop a new paper manufacturing process that derives high-quality paper sourced from hemp and agriculture waste. Agrix Paper will reinvent the papermaking process for a more green and sustainable future.
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As part of MS Thesis we developed electrostatic simulator for DG SOI devices by implementing the self consistent full band Schrodinger Poisson solver. We used the Empirical Pseudopotential method in conjunction with supercell approach to solve the Schrodinger Equation. EPM was chosen because it has few empirical parameters which give us good accuracy for experimental results. Also EPM is computationally less expensive as compared to the atomistic methods like DFT(Density functional theory) and NEGF (Non-equilibrium Green's function). In our workwe considered two crystallographic orientations of Si,namely [100] and [110].
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This research rst discusses a 2D planar MOSFET simulator and its numerical solver, pointing out its performance limit. By analyzing the algorithm complexity, Multigrid method is proposed to replace conventional Successive-Over-Relaxation method in a numerical solver. A variety of Multigrid methods (standard Multigrid, Algebraic Multigrid, Full Approximation Scheme, and Full Multigrid) are discussed and implemented. Their properties are examined through a set of numerical experiments. Finally, Algebraic Multigrid, Full Approximation Scheme and Full Multigrid are integrated into one advanced numerical solver based on the exact requirements of a semiconductor device simulator. A 2D MOSFET device is used to benchmark the performance, showing that the advanced Multigrid method has higher speed, accuracy and robustness.
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First, the electromechanical properties of 1,4-benzenedithiol molecular junctions are investigate. Counterintuitively, the conductance of this molecule is found to increase by more than an order of magnitude when stretched. This conductance increase is found to be reversible when the molecular junction is compressed. The current-voltage, conductance-voltage and inelastic electron tunneling spectroscopy characteristics are used to attribute the conductance increase to a strain-induced shift in the frontier molecular orbital relative to the electrode Fermi level, leading to resonant enhancement in the conductance.
Next, the effect of stretching-induced structural changes on charge transport in DNA molecules is studied. The conductance of single DNA molecules with lengths varying from 6 to 26 base pairs is measured and found to follow a hopping transport mechanism. The conductance of DNA molecules is highly sensitive to mechanical stretching, showing an abrupt decrease in conductance at surprisingly short stretching distances, with weak dependence on DNA length. This abrupt conductance decrease is attributed to force-induced breaking of hydrogen bonds in the base pairs at the end of the DNA sequence.
Finally, the effect of small mechanical modulation of the base separation on DNA conductance is investigated. The sensitivity of conductance to mechanical modulation is studied for molecules of different sequence and length. Sequences with purine-purine stacking are found to be more responsive to modulation than purine-pyrimidine sequences. This sensitivity is attributed to the perturbation of &pi-&pi stacking interactions and resulting effects on the activation energy and electronic coupling for the end base pairs.
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A 3-D technology computer aided design (TCAD) device simulation is done to compare the performance of FinFET and GAA nanowire structures with vertically stacked horizontal nanowires. Subthreshold slope, DIBL & saturation current are measured and compared between these devices. The FinFET’s device performance has been matched with the ASAP7 compact model with the impact of tensile and compressive strain on NMOS & PMOS respectively. Metal work function is adjusted for the desired current drive. The nanowires have shown better electrostatic performance over FinFETs with excellent improvement in DIBL and subthreshold slope. This proves that horizontal nanowires can be the potential candidate for 5 nm technology node. A GAA nanowire structure for 5 nm tech node is characterized with a gate length of 15 nm. The structure is scaled down from 7 nm node to 5 nm by using a scaling factor of 0.7.