Ashish K. Gupta

Waste reduction through multicomponent mass exchange network synthesis

Abstract We have developed the “mass exchange network (MEN)” synthesis concept to provide solutions for waste-minimization problems. Often, waste reduction problems require the removal of multiple toxic species from plant streams. Aside from the transfer of multiple chemical species multicomponent problems also encompasses simultaneous heat and mass exchange. To address this problem, we employ the recently proposed “State Space Approach.” The State Space Approach decomposes the network synthesis problem into the evaluation of an operator —where the actual unit operations are defined, and the distribution network —which contains all the flows to and from the operator. The entire network is optimized simultaneously. The use of distinct subnetworks for the flows and unit operations gives complete flexibility to choose over all possible configurations. The proposed approach is illustrated through an example from recycle-reuse tasks; the removal of nitrogenous compounds from the waste streams of a fertilizer plant.

Shifted-contour auxiliary-field Monte Carlo for molecular electronic structure

The shifted-contour auxiliary-field Monte Carlo (SCAFMC) approach has been recently developed by Rom, Charutz and Neuhauser as an extension of the auxiliary-field Monte Carlo (AFMC) method. AFMC replaces the difficult fully interacting electrons problem by an ensemble of simpler problems where the electrons interact with a fluctuating electric field but not with each other. SCAFMC is based on shifting the auxiliary-field contour of integration to pass through the (imaginary) stationary point, leading to numerical stability at long propagation times. The new approach converges to the full CI energy in electronic structure calculations (both ground and low-lying excited states). Here we expand the application of SCAFMC from atomic to molecular problems. First, we calculate ground-state energies of a highly correlated transition-metal system (Cr2) with a moderate (12 orbitals) active space size, and demonstrate that SCAFMC is able to extract the energies accurately. In addition, we use SCAFMC to calculate a ...

Initial state laser control of curve‐crossing reactions using the Rayleigh–Ritz variational procedure

A new two‐step procedure for laser control of photodissociation is presented. In the first step of the procedure, we show that control of photodissociation product yields can be exerted through preparation of the initial wave function prior to application of the photodissociation field in contrast to previous laser control studies where attention has focused on the design of the field which induces dissociation. Specifically, for a chosen channel from which maximum product yield is desired and a given photodissociation field, the optimal linear combination of vibrational eigenstates which comprise the initial wave function is found using a straightforward variational calculation. Any photodissociation pulse shape and amplitude can be assumed since the Schrodinger equation is solved directly. Application of this method to control of product yields in the photodissociation of hydrogen iodide is demonstrated. The second step of the control procedure involves the preparation of the coherent superposition of d...

Use of modified smooth exterior scaling method as an absorbing potential and its application

Here, we propose a new complex path to achieve better absorption during the propagation of a wavepacket. In the proposed modified smooth exterior scaling (SES) method, scaling function, θ(x), has been chosen as a real function rather than complex (as used in a conventional smooth exterior scaling method). It greatly reduces the artificial reflections from the boundary edges. This modified SES method is applied to study the multiphoton dissociation of H(2)(+) in intense laser field. The resonance states are calculated accurately.

AN EFFICIENT METHOD FOR DETERMINING QUANTUM DYNAMICS IN STRONG FIELDS BY INTEGRATING THROUGH AMPLITUDE AND FREQUENCY PARAMETER SPACE

A new method which computes the dynamics of molecular systems under the influence of a strong field is presented. Eigenvalues and eigenfunctions of the time-dependent Schrodinger equation are obtained and integrated over a range of field amplitudes and frequencies, and the evolution of the wavefunction is determined using Floquet formalism. With this method, it is possible to predict the wavefunction dynamics for an arbitrary range of field intensities and wavelengths by solving the time-dependent Schrodinger equation only once or, in some cases, by not solving it at all, even though the field intensities are well within the nonperturbative regime. Large savings in computational time are demonstrated in application of the method to vibrational excitation of hydrogen fluoride.

Control of harmonic generation by initial-state preparation

Abstract A procedure to control harmonic generation is proposed using initial state control. We show that an initial molecular state can be prepared before shining a strong laser pulse to maximize the output harmonic generation. We demonstrate the method by maximizing emission for the sixth harmonic on a given initial IR pulse in a model H 2 + system using five initial vibrational states.

Improving services in outdoor patient departments by focusing on process parameters: a simulation approach

The paper examines working of outdoor patient departments in a general hospital. There are several inpatient wards and out-patient departments and hundreds of patients visited the hospital daily for treatment. The place is chaotic and noisy, especially in the morning. The current performance is evaluated and newer ways are identified to measure the performance of the hospital. Various alternatives are evaluated by simulating each of them. As against the commonly held view that there is a shortage of staff in the hospital, it is actually a problem of maintaining discipline and scheduling of staff. Further, there is a need to change the way activities are performed. The paper also suggests ways of measuring process oriented performance of Outdoor Patients Department (OPD) and OPD registration counters.

Application of parametric equations of motion to study the laser induced multiphoton dissociation of H2+ in intense laser field

We have applied parametric equations of motion (PEM) to study photodissociation dynamics of H(2)(+). The resonances are extracted using smooth exterior scaling method. This is the first application of PEM to non-Hermitian Hamiltonian that includes resonances and the continuum. Here, we have studied how the different resonance states behave with respect to the change in field amplitude. The advantage of this method is that one can easily trace the different states that are changing as the field parameter changes.

Application of smooth exterior scaling method to calculate the high harmonic generation spectra

We have calculated the high harmonic generation spectra from Xe atom by imposing different kinds of absorbing potentials. Owing to the center of inversion of the model system, one should get odd harmonics only. However, using negative imaginary potentials as an absorbing boundary condition, we have also got even order harmonics along with the odd order harmonics. These non-odd order harmonics are generated due to the spurious reflections occurring at the grid boundary. On the contrary, when smooth exterior scaling methods are used as an absorbing boundary condition, only odd order harmonics are obtained. Hence, smooth exterior scaling methods impose proper absorbing boundary condition.

Distinguishing between aligned and randomly oriented polar molecules by using a combination of strong laser field with a weak static field

The harmonic generation spectra (HGS) of two different ensembles of the same heteronuclear (polar) diatomic molecule are studied. In one ensemble the molecules are aligned (i.e. CO ↔ OC) whereas in the second ensemble the molecules are randomly distributed in different directions (and therefore not all molecules have the same orientation, e.g. CO or OC along one of the axes in the laboratory frame). Using the non-Hermitian formalism of quantum mechanics we prove that the HGS of the two ensembles consist of odd-order harmonics only, provided the photo-induced dynamics is controlled by a single resonance (metastable) state. As we show here by using the Friedrich and Herschbach approach [J. Phys. Chem. A 103, 10280 (1999); J. Chem. Phys. 111, 6157 (1999)], it is possible to distinguish between the ensemble of ‘perfectly’ aligned molecules and an ensemble of molecules with a random directional distribution, provided the dc-field is turned on adiabatically slow and all aligned molecules are in the same quantum state. As an illustrative numerical example the HGS of aligned and ensemble of random directional distributed CO molecules with and without dc field were computed by carrying out ab initio electronic structure calculations.