Engineering topics

Kumar, R.

Publications and source records attributed to Kumar, R..

At least 19 records

DOE OSTI2026

The ePIC dual-radiator RICH detector

The dual radiator Ring Imaging Cherenkov (dRICH) detector is required to provide continuous hadron identification from ≈3 GeV/c up to ≈50 GeV/c, and to supplement electron and positron identification from a few hundred MeV/c up to about 15 GeV/c, in the forward (ion-side) end-cap of the ePIC experiment. Such an extended momentum range imposes the use of two radiators, gas and aerogel. The common imaging system, that ensures compactness and cost-effectiveness, is based on SiPM sensors to work in a high non-uniform magnetic field. During the R&D phase, the dual radiator principle and the single component performance have been validated. A status overview of the project is presented. The design and technological choices are discussed together with the results obtained from laboratory characterization of the component demonstrators and beam tests of the evolving prototypes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

Deformation of the $0^+_{1,2}$ states in 110 Cd from low-energy Coulomb excitation

Electromagnetic properties of 110 Cd were studied via low-energy Coulomb excitation with 32 S and 14 N beams. Magnitudes and relative signs of eight E2 matrix elements, including quadrupole moments of the $2^+_1$ and $2^+_2$ states, were determined using the least-squares code GOSIA. From those, quadrupole deformation parameters of the $0^+_{1,2,3}$ states were inferred, providing for the first time conclusive evidence for the non-axial character of the ground state in 110 Cd. The experimental results were compared with new calculations using the general quadrupole collective Bohr Hamiltonian model with SLy4 and UNEDF0 interactions. The non-axiality of the ground state is reproduced by the present calculations, independently of the interaction used.

Collective models↗

DOE OSTI2025

Pressure tuning of Kitaev spin liquid candidate Na$_3$Co$_2$SbO$_6$goo

The search for Kitaev's quantum spin liquid (KQSL) state in real materials has recently expanded with the prediction that honeycomb lattices of divalent, high-spin cobalt ions could host the dominant bond-dependent exchange interactions required to stabilize the elusive entangled quantum state. The layered honeycomb Na$_3$Co$_2$SbO$_6$ has been singled out as a leading candidate provided that the trigonal crystal field acting on Co $3d$ orbitals, which enhances non-Kitaev exchange interactions between $J_{\rm eff}=\frac{1}{2}$ spin-orbital pseudospins, is reduced. We find that applied pressure leads to anisotropic compression of the layered structure, significantly reducing the trigonal distortion of CoO$_6$ octahedra. A strong enhancement of ferromagnetic correlations between pseudospins is observed in the spin-polarized (3 Tesla) phase up to about 60 GPa. Higher pressures drive a spin transition into a low-spin state destroying the $J_{\rm eff}=\frac{1}{2}$ local moments required to map the spin Hamiltonian into Kitaev's model. The spin transition strongly suppresses the low-temperature magnetic susceptibility and appears to stabilize a paramagnetic phase driven by frustration. Although applied pressure fails to realize a KQSL state, the possible emergence of frustrated magnetism of localized, low-spin $S=\frac{1}{2}$ moments opens the door for exploration of novel magnetic quantum states in compressed honeycomb lattices of divalent cobaltates.

FOS: Physical sciences↗

DOE OSTI2024

M IV /Co –I (M = Zr, Hf) Bis(phosphinoamide) Complexes with η 6 - and η 4 -Arenes

Despite their relevance to catalysis, low-/subvalent cobalt complexes are difficult to synthesize and isolate. Consequently, very few “cobaltate” complexes are known and there is a lack of architectural diversity in this field. Lewis acidic d 0 group IV metals have been demonstrated to stabilize Co –I centers via metal–metal bonds. Herein, we report the synthesis of bis(phosphinoamide) heterobimetallic M IV /Co –I arene complexes (M = Zr, Hf). The driving force to maintain the aromaticity of the arenes dictates the hapticity of the Co-bound arene ligands and influences the binding arrangement of the phosphinoamide ligands. Benzene and toluene were observed to bind η 6 to the Co –I center, forcing dissociation of one of the phosphinoamide ligands, whereas η 4 -coordination of anthracene allows both phosphinoamide ligands to remain bound to the Co center. The identity of both the arene and the group IV metal ion starkly influence the lability of the arene. For instance, the Co-bound benzene ligand in the Zr IV /Co –I benzene complex rapidly exchanges with C 6 D 6 in solution, whereas toluene/C 6 D 6 exchange is much slower and appreciable C 6 H 6 /C 6 D 6 exchange is not observed for the Hf analogue. The Zr IV /Co –I benzene complex loses benzene upon repeated exposure to vacuum to form an arene-free tetrametallic dimer.

aromatic compounds↗

NASA NTRS2020

NASA-ISRO Synthetic Aperture Radar (NISAR) Mission

UNKNOWN

Sarma, C.↗

NASA NTRS1992

Multi-element array signal reconstruction with adaptive least-squares algorithms

Two versions of the adaptive least-squares algorithm are presented for combining signals from multiple feeds placed in the focal plane of a mechanical antenna whose reflector surface is distorted due to various deformations. Coherent signal combining techniques based on the adaptive least-squares algorithm are examined for nearly optimally and adaptively combining the outputs of the feeds. The performance of the two versions is evaluated by simulations. It is demonstrated for the example considered that both of the adaptive least-squares algorithms are capable of offsetting most of the loss in the antenna gain incurred due to reflector surface deformations.

Kumar, R.↗

NASA NTRS1990

A novel multireceiver communications system configuration based on optimal estimation theory

A multireceiver configuration for the purpose of carrier arraying and/or signal arraying is presented. Such a problem arises for example, in the NASA Deep Space Network where the same data-modulated signal from a spacecraft is received by a number of geographically separated antennas and the data detection must be efficiently performed on the basis of the various received signals. The proposed configuration is arrived at by formulating the carrier and/or signal arraying problem as an optimal estimation problem. Two specific solutions are proposed. The first solution is to simultaneously and optimally estimate the various phase processes received at different receivers with coupled phase locked loops (PLLs) wherein the individual PLLs acquire and track their respective receivers' phase processes, but are aided by each other in an optimal manner. However, when the phase processes are relatively weakly correlated, and for the case of relatively high values of symbol energy-to-noise spectral density ratio, a novel configuration for combining the data modulated, loop-output signals is proposed. The scheme can be extended to the case of low symbol energy-to-noise case by performing the combining/detection process over a multisymbol period. Such a configuration results in the minimization of the effective radio loss at the combiner output, and thus a maximization of energy per bit to noise-power spectral density ration is achieved.

Kumar, R.↗

NASA NTRS1990

Application of a novel multi-stage signal parameter estimator to high dynamic GPS receivers

The performance of a novel multistage estimator when applied to the estimation of the position, velocity, and acceleration of high dynamic Global Positioning System (GPS) receivers is discussed. For the present application, a two-stage specialization of the more general estimation scheme is considered, wherein the first-stage algorithm is selected to be a modified least-squares algorithm operating upon the differential signal model and referred to as differential least-squares (DLS) and the second stage is simply an extended Kalman filter (EKF). In terms of the threshold on received carrier power-to-noise power spectral density ratio (CNR), when compared to the single-stage EKF algorithm, the DLS-EKF algorithm is about 1.5-2.0 dB better in terms of threshold and outperforms the crossproduct AFC (automatic frequency control) loop by 2-5 dB. For the case when data modulation is present, the proposed scheme provides an improvement of about 6 dB in terms of CNR compared to an earlier approximate MLE (maximum likelihood estimation) scheme. There are also very significant improvements in terms of other performance measures.

Kumar, R.↗

NASA NTRS1989

Frequency Estimation Techniques For High Dynamic Trajectories

Report presents comparative study of four techniques for estimating frequency of sinusoidal signal received in presence of noise when transmitter and/or receiver experiencing very high dynamics. Four techniques involve approximate-maximum-likelihood estimator, extended Kalman filter, cross-product automatic frequency control loop, and digital phase locked loop, respectively. In numerical simulations, each technique applied to signal from transmitter maneuvering along common trajectory; performance of each examined to determine its useful operating range, and performances compared.

Vilnrotter, V. A.↗

NASA NTRS1989

Application of adaptive least-squares algorithm to multi-element array signal reconstruction

Results are presented in terms of the performance improvement of a multi-feed array configuration over the usual single feed system when an adaptive least-squares algorithm is applied for the signal reconstruction. Two versions of the least-squares algorithm are presented, one of which is based on the maximization of the signal-to-noise ratio while the other is based on the deconvolution of received signal field. These algorithms were developed for the purpose of minimizing degradations arising from various sources, which can severely limit the performance (gain) of a single-feed system.

Kumar, R.↗

NASA NTRS1988

Efficient detection and signal parameter estimation with applications to high dynamic GPS receivers

A novel technique for simultaneously detecting data and estimating the parameters of a received carrier signal phase modulated by unknown data and experiencing very high Doppler, Doppler rate, etc. is discussed. Such a situation arises, for example, in the case of Global Positioning Systems (DPS) where the signal parameters are directly related to the position, velocity and acceleration of the GPS receiver. The proposed scheme is based upon first estimating the received signal local (data dependent) parameters over two consecutive bit periods, followed by the detection of a possible jump in these parameters. The presence of a detected jump signifies a data transition which is then removed from the received signal. This effectively demodulated signal is then processed to provide the estimates of global (data independent) parameters of the signal related to the position, velocity, etc. of the receiver. One of the key features of the proposed algorithm is the introduction of two different schemes which can provide an improvement of up to 3 dB over the conventional implementation of Kalman filter as applied to phase and frequency estimation, under low to medium signal-to-noise ratio conditions.

Kumar, R.↗

NASA NTRS1988

A comparison of frequency estimation techniques for high-dynamic trajectories

A comparison is presented for four different estimation techniques applied to the problem of continuously estimating the parameters of a sinusoidal Global Positioning System (GPS) signal, observed in the presence of additive noise, under extremely high-dynamic conditions. Frequency estimates are emphasized, although phase and/or frequency rate are also estimated by some of the algorithms. These parameters are related to the velocity, position, and acceleration of the maneuvering transmitter. Estimated performance at low carrier-to-noise ratios and high dynamics is investigated for the purpose of determining the useful operating range of an approximate Maximum Likelihood (ML) estimator, an Extended Kalman Filter (EKF), a Cross-Product Automatic Frequency Control (CPAFC) loop, and a digital phase-locked loop (PPL). Numerical simulations are used to evaluate performance while tracking a common trajectory exhibiting high dynamics.

Vilnrotter, V. A.↗

NASA NTRS1987

Fixed lag smoothers for carrier phase and frequency tracking

The application of fixed lag smoothing algorithms are presented for the problem of estimation of the phase and frequency of a sinusoidal carrier received in the presence of process noise and additive observation noise. A suboptimal structure consists of a phase-locked loop (PLL) followed by a post loop correction to the phase and frequency estimates. When the PLL is operating under a high signal-to-noise ratio, the phase detector is approximately linear, and the smoother equations then correspond to the optimal linear equations for an equivalent linear signal model. The performance of such a smoother can be predicted by the linear filtering theory. However, if the PLL is operating near the threshold region of the signal to noise ratio, the phase detector cannot be assumed to be linear. Then the actual performance of the smoother can significantly differ from that predicted by linear filtering theory. Both the theoretical and simulated performance of such smoothers derived on the basis of various models for the phase of frequency processes are presented.

Kumar, R.↗

NASA NTRS1987

Improvement of cloud cover assessment of Landsat Thematic Mapper data

Various methods for cloud cover assessment of Landsat TM data are compared and evaluated. A total of 3906 TM 241-mm black-and-white photo prints of different seasons and regions were assessed manually. These images were mostly in band 4 (0.76-0.90 microns) for daytime data and band 6 (10.4-12.5 microns) for nighttime data. The results of this manual assessment are compared to available automated and manual assessments, and the differences between results obtained by various methods are discussed.

Ludwig, R.↗

NASA NTRS1986

A comparison of methods for DPLL loop filter design

Four design methodologies for loop filters for a class of digital phase-locked loops (DPLLs) are presented. The first design maps an optimum analog filter into the digital domain; the second approach designs a filter that minimizes in discrete time weighted combination of the variance of the phase error due to noise and the sum square of the deterministic phase error component; the third method uses Kalman filter estimation theory to design a filter composed of a least squares fading memory estimator and a predictor. The last design relies on classical theory, including rules for the design of compensators. Linear analysis is used throughout the article to compare different designs, and includes stability, steady state performance and transient behavior of the loops. Design methodology is not critical when the loop update rate can be made high relative to loop bandwidth, as the performance approaches that of continuous time. For low update rates, however, the miminization method is significantly superior to the other methods.

Aguirre, S.↗

NASA NTRS1986

Fast frequency acquisition via adaptive least squares algorithm

A new least squares algorithm is proposed and investigated for fast frequency and phase acquisition of sinusoids in the presence of noise. This algorithm is a special case of more general, adaptive parameter-estimation techniques. The advantages of the algorithms are their conceptual simplicity, flexibility and applicability to general situations. For example, the frequency to be acquired can be time varying, and the noise can be nonGaussian, nonstationary and colored. As the proposed algorithm can be made recursive in the number of observations, it is not necessary to have a priori knowledge of the received signal-to-noise ratio or to specify the measurement time. This would be required for batch processing techniques, such as the fast Fourier transform (FFT). The proposed algorithm improves the frequency estimate on a recursive basis as more and more observations are obtained. When the algorithm is applied in real time, it has the extra advantage that the observations need not be stored. The algorithm also yields a real time confidence measure as to the accuracy of the estimator.

Kumar, R.↗

NASA NTRS1986

A class of optimum digital phase locked loops

This paper presents a class of optimum digital filters for digital phase locked loops, for the important case in which the maximum update rate of the loop filter and numerically controlled oscillator (NCO) is limited. This case is typical when the loop filter is implemented in a microprocessor. In these situations, pure delay is encountered in the loop transfer function and thus the stability and gain margin of the loop are of crucial interest. The optimum filters designed for such situations are evaluated in terms of their gain margin for stability, dynamic error, and steady-state error performance. For situations involving considerably high phase dynamics an adaptive and programmable implementation is also proposed to obtain an overall optimum strategy.

Kumar, R.↗

NASA NTRS1985

A class of optimum digital phase locked loops for the DSN advanced receiver

A class of optimum digital filters for digital phase locked loop of the deep space network advanced receiver is discussed. The filter minimizes a weighted combination of the variance of the random component of the phase error and the sum square of the deterministic dynamic component of phase error at the output of the numerically controlled oscillator (NCO). By varying the weighting coefficient over a suitable range of values, a wide set of filters are obtained such that, for any specified value of the equivalent loop-noise bandwidth, there corresponds a unique filter in this class. This filter thus has the property of having the best transient response over all possible filters of the same bandwidth and type. The optimum filters are also evaluated in terms of their gain margin for stability and their steady-state error performance.

Hurd, W. J.↗