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Gupta, P. K.

Publications and source records attributed to Gupta, P. K..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Real-Time Modeling of Thermal Interactions in Cryogenic Ball Bearings

Based on the integration of classical differential equations of motion of bearing elements, a real-time dynamic simulation of ball bearing performance is coupled with simultaneous modeling of thermal interactions between the bearing elements. The transient heat generations are time averaged over a significantly larger time step before they are used to compute the changes in bearing temperature fields. Such an averaging algorithm eliminates the numerical difficulties associated with simultaneous integration of mechanical thermal differential equations with vastly different time scales. Under stable operation, the step change in temperatures at each thermal time step converges to a steady-state solution. Following is a list of accomplishments in the present investigation: (1) A real-time dynamic performance of both 440C and hybrid ball bearings in a LOX environment is modeled in both transient and steady-state time domains, as the inner race accelerates to a prescribed operating speed. (2) The frictional interactions at the ball to race contacts are modeled by experimentally measured traction coefficients as a function of slide-to-roll ratios. (3) Bearing heat generation, as defined by the heat transferred to circulating LOX, is validated against experimental values determined by measured LOX temperatures under prescribed pressures and flow rates. The predicted heat generation is in good agreement with the experimental values. (4) The steady-state solutions are shown to be independent of initial conditions. This establishes convergence of the numerical integration of a differential equation of motion of the bearing elements. (5) Churning and drag losses in the circulating LOX constitutes the majority of bearing heat generation under the experimental test conditions. (6) The heat dissipated in frictional interactions in hybrid bearings is significantly lower in hybrid bearings in comparison to that simulated in all-steel bearings, while the churning and drag losses are relatively unchanged.

Gupta, P. K.↗
DOE OSTI2016

Strong magnetoelectric and spin phonon coupling in SmFeO{sub 3}/PMN-PT composite

We have investigated spin phonon coupling in the strain coupled magnetoelectric SmFeO{sub 3}/0.65Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.35PbTiO{sub 3} (PMN-PT) composite in the temperature range of 300–650 K by Raman spectroscopy and magnetic measurements. The SmFeO{sub 3}/PMN-PT composite shows sharp rise in magnetic moment across ferroelectric transition temperature (T{sub c}) of PMN-PT. Around this transition temperature (T{sub c} of PMN-PT), the temperature evolution of Raman spectra of the composite also shows anomalies in the phonon frequencies and line width corresponding to the SmFeO{sub 3} phase which indicate structural modifications in the SmFeO{sub 3} phase around T{sub c} of PMN-PT. The observed structural, magnetic, and phonon anomalies of SmFeO{sub 3} around T{sub c} of PMN-PT in SmFeO{sub 3}/PMN-PT are attributed to spin-phonon coupling providing evidence of strong strain mediated magnetoelectric effects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Solid state synthesis, crystal growth and optical properties of urea and p-chloronitrobenzene solid solution

Urea is an attractive material for frequency conversion of high power lasers to UV (for wavelength down to 190 nm), but its usage is hindered due to its hygroscopic nature, though there is no alternative organic NLO crystal which could be transparent up to 190 nm. The hygroscopic character of urea has been modified by making the solid solution (UCNB) of urea (U) and p-chloronitrobenzene (CNB). The formation of the solid solution of CNB in U is explained on the basis of phase diagram, powder XRD, FTIR, elemental analysis and single crystal XRD studies. The solubility of U, CNB and UCNB in ethanol solution is evaluated at different temperatures. Transparent single crystals of UCNB are grown from its saturated solution in ethanol. Optical properties e.g., second harmonic generation (SHG), refractive index and the band gap for UCNB crystal were measured and their values were compared with the parent compounds. Besides modification in hygroscopic nature, UCNB has also shown the higher SHG signal and mechanical hardness in comparison to urea crystal. - Highlights: • The hygroscopic character of urea was modified by making the solid solution • Solid solution formation is support by elemental, powder- and single crystal XRD • Crystal of solid solution has higher SHG signal and mechanical stability. • Refractive index and band gap of solid solution crystal have determined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Synthesis and characterization of carboxymethyl cellulose from office waste paper: A greener approach towards waste management

Highlights: • Carboxymethyl cellulose (CMC) was successfully prepared from waste paper. • CMC had maximum degree of substitution (DS) 1.07. • Rheological studies of CMC (DS, 1.07) showed non-Newtonian pseudoplastic behavior. • Characterization of CMC was done by FT-IR and NMR techniques. • Morphology of prepared CMC was studied by SEM. - Abstract: In the present study, functionalization of mixed office waste (MOW) paper has been carried out to synthesize carboxymethyl cellulose, a most widely used product for various applications. MOW was pulped and deinked prior to carboxymethylation. The deinked pulp yield was 80.62 ± 2.0% with 72.30 ± 1.50% deinkability factor. The deinked pulp was converted to CMC by alkalization followed by etherification using NaOH and ClCH{sub 2}COONa respectively, in an alcoholic medium. Maximum degree of substitution (DS) (1.07) of prepared CMC was achieved at 50 °C with 0.094 M and 0.108 M concentrations of NaOH and ClCH{sub 2}COONa respectively for 3 h reaction time. The rheological characteristics of 1–3% aqueous solution of optimized CMC product showed the non-Newtonian pseudoplastic behavior. Fourier transform infra red (FTIR), nuclear magnetic resonance (NMR) and scanning electron microscope (SEM) study were used to characterize the CMC product.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Spectroscopic analysis on the basis Judd–Ofelt theory of Nd{sup 3+} in (Y{sub 0.985}Nd{sub 0.015}){sub 2}O{sub 3}: A transparent laser-host ceramic

Highlights: • Transparent Y{sub 2}O{sub 3} ceramic with 1.5 atm% doping of neodymium (Nd) was fabricated and its spectroscopic properties were investigated using Judd–Ofelt theory. • The Judd–Oflet parameters, computed from the absorption bands of Nd{sup 3+} ion, are Ω{sub 2} = 8.84 × 10{sup −20} cm{sup 2}, Ω{sub 4} = 9.82 × 10{sup −20} cm{sup 2} and Ω{sub 6} = 4.44 × 10{sup −20} cm{sup 2}. These parameters were used to determine absorption line strength, radiative transition probabilities, fluorescence branch ratio and radiative lifetime for different transitions of Nd{sup 3+}. • The branching ratios for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition are 0.548 and 0.389, respectively. The spectroscopic quality factor was determined to be 2.21, which is higher than 1.0 atm% neodymium doped Y{sub 2}O{sub 3} ceramic. A calculated radiation decay time (τ = 140 μs) is reasonably close to the experimentally measured life time (153 μs). The life time for 1.5 mol% Nd doped Y{sub 2}O{sub 3} ceramic which is lower than that of 1.0 atm% neodymium doped ceramic. The lowering of life time was attributed to the presence of concentration quenching effects. • The room temperature emission cross-section for individual Stark bands of {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transitions was determined. The total emission cross section for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition was found to be 25.49 × 10{sup −20} and 37.04 × 10{sup −20} cm{sup 2}, which is significantly higher than 1.0 atm% Nd{sup 3+} doped Y{sub 2}O{sub 3}ceramic. - Abstract: Spectroscopic investigation of 1.5 atm% Nd{sup 3+} doped Y{sub 2}O{sub 3} transparent ceramic was performed for different emission wavelengths. Judd–Oflet parameters, computed from the absorption bands of Nd{sup 3+} ion, are Ω{sub 2} = 8.84 × 10{sup −20} cm{sup 2}, Ω{sub 4} = 9.82 × 10{sup −20} cm{sup 2} and Ω{sub 6} = 4.44 × 10{sup −20} cm{sup 2}. These parameters were used to determine absorption line strength, radiative transition probabilities, fluorescence branch ratio and radiative lifetime for different transitions of Nd{sup 3+}. The branching ratios for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition are 0.548 and 0.389, respectively. The calculated radiative lifetime (140 μs) is in good agreement with the measured lifetime (153 μs). The room temperature emission cross-section of individual Stark bands of {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transitions was determined. The total emission cross section for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition was found to be 25.49 × 10{sup −20} and 37.04 × 10{sup −20} cm{sup 2}, which is significantly higher than 1.0 atm% Nd{sup 3+} doped Y{sub 2}O{sub 3}ceramic.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Growth and characterization of undoped and Mn doped lead-free piezoelectric NBT–KBT single crystals

Highlights: • Single crystals of undoped and Mn doped NKBT crystals are grown by spontaneous nucleation. • Temperature and frequency dependent dielectric constant and loss are measured. • Dielectric constant has increased and the loss has reduced on Mn doped NKBT. • Concentration of oxygen vacancies has been reduced in Mn doped NKBT. • The activation energy for undoped and Mn doped NKBT are calculated. - Abstract: Lead-free piezoelectric single crystals of undoped and 1 wt% Mn doped 0.80 Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}–0.20 K{sub 0.5}Bi{sub 0.5}TiO{sub 3} (NKBT) was grown using self-flux. Powder X-ray diffraction analysis revealed that the grown crystals belong to tetragonal system at room temperature. The lattice strain was calculated from Williamson Hall relation for undoped and Mn doped NKBT crystals. A significant change is observed in dielectric behavior of Mn doped NKBT when compared to undoped sample. The diffuseness increased substantially on Mn doped NKBT which masked the ferroelectric to antiferroelectric transition in the dielectric constant plot. The AC impedance study revealed that the conduction is governed by the singly ionized oxygen vacancy. Further, the decrease in the conductivity on Mn doping suggests that Mn replaces the Bi vacancy, which reduces the oxygen vacancy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural, electrical and magnetic properties of Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3}, and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} multiferroics

Graphical abstract: - Highlights: • Samples synthesized by solid state reaction route successfully. • La and Pb substitutions significantly change the BiFeO{sub 3} crystal symmetry. • The presence of E(TO9) and E(LO9) modes indicates ferroelectric domain of BiFeO{sub 3}. • Doped ions and crystal structure affect the dielectric properties of the samples. • The observed value of conductivity for BPFO sample is 3.1 × 10{sup −9} σ{sup −1} cm{sup −1}. - Abstract: Single-phase BiFeO{sub 3}, Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3} and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} ceramic samples were prepared via solid state reaction route to study the effects of co-doping (La/Pb) on their crystal structure and ferroelectromagnetic behaviour. X-ray diffraction data accompanied by Rietveld refinement showed that BiFeO{sub 3} crystallize in rhombohedral distorted perovskite structure (space group-R3c) while to that BPFO and BLPFO crystallize in tetragonal (P4/mmm) symmetry. Presence of E(TO9) and E(LO9) modes in Raman scattering spectra for BiFeO{sub 3} and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} infers ferroelectric nature. However, absence of both modes in Bi{sub 0.875}Pb{sub 0.175}FeO{sub 3} indicates the paraelectric nature. The room temperature dielectric constant (10 Hz–1 MHz) of BiFeO{sub 3}, Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3} and Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} is about 100, 60, and 200. Ferroelectromagnetic measurements revealed the existence of ferroelectricity with remnant polarization of 0.24 μC/cm{sup 2} in Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3}, paraelectricity in Bi{sub 0.875}Pb{sub 0.175}FeO{sub 3}, and weak (strong) ferromagnetism with remnant magnetizations of 0.25 (1.57) emu/g in Bi{sub 0.725}La{sub 0.1}Pb{sub 0.175}FeO{sub 3} (Bi{sub 0.825}Pb{sub 0.175}FeO{sub 3})

36 MATERIALS SCIENCE↗
DOE OSTI2013

Evidence of spin phonon coupling in magnetoelectric NiFe{sub 2}O{sub 4}/PMN-PT composite

The coupling of phonon with spin in strain coupled magnetoelectric NiFe{sub 2}O{sub 4} (NFO)/0.65Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.35PbTiO{sub 3} (PMN-PT) composite was investigated by temperature-dependent Raman spectroscopy and magnetic measurements in the range 30–350 °C. Pure NFO shows usual ferromagnetic behaviour in this temperature range while NFO/PMN-PT composite show dramatic change in magnetic moment across ferroelectric transition temperature (T{sub c} ∼ 180 °C) of PMN-PT. The temperature evolution of the Raman spectra for the composite shows significant phonon anomalies in T-site (Fe-O) and O-site (Ni/Fe-O) phonon modes at ferroelectric transition temperature is attributed to spin phonon coupling in NFO/PMN-PT composite. The strain mediated magnetoelectric coupling mechanism in this composite is apparent from the observed spin phonon interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Spectroscopic analysis on the basis of Judd–Ofelt theory along [0 0 1] of Er:YVO{sub 4} grown by optical floating zone technique

Highlights: ► Synthesis and solid state reaction for Er:YVO{sub 4} is addressed. ► Single crystal growth by OFZ technique along c [0 0 1] is discussed. ► Differences in crystal morphology along a and c axes are experimentally observed. ► This is explained on the basis of difference in attachment energy. ► Spectroscopic investigations along [0 0 1] are carried out. - Abstract: 1.0 at.% erbium-doped YVO{sub 4} crystals have been grown along [0 0 1] by optical floating zone technique after optimizing the synthesis process. The circular cross-section of the grown crystals is explained on the basis of attachment energy. Using Judd–Ofelt (JO) theory the absorption and emission lines observed in absorption and photoluminescence data along [0 0 1] are characterized. JO intensity parameters as calculated are: Ω{sub 2} = 14.4389 × 10{sup −20} cm{sup 2}, Ω{sub 4} = 2.3320 × 10{sup −20} cm{sup 2} and Ω{sub 6} = 1.7794 × 10{sup −20} cm{sup 2}. For {sup 4}I{sub 13/2} → {sup 4}I{sub 15/2} transition the calculated radiative lifetime and emission cross-section are: 2.59 × 10{sup −20} cm{sup 2} and 2.45 ms, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Study of de-watering from the gelatinous precipitate formed during co-precipitation of Nd-YAG powder

Neodymium doped Yttrium Aluminium Garnet (Nd:YAG) ceramics have been synthesised using coprecipitation technique and high temperature vacuum sintering. Gelatinous like precipitates were obtained when precursors of Nd, Al and Yb-nitrate solutions are co-precipitated using ammonia co-precipitant. De-watering from the gelatinous like precipitates is a big challenge and it possesses difficulty in filtration. Evaporation of water by heating resulted in strong agglomerated powder. Different agents were used to ease the filtration process, which is correlated with the phase in the calcined powder.

36 MATERIALS SCIENCE↗
NASA NTRS1998

Manufacture of porous biodegradable polymer conduits by an extrusion process for guided tissue regeneration

We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.

NASA Discipline Cell Biology↗
NASA NTRS1974

Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 2: Elastomer characteristics at constant temperature

Dynamic properties of a commerical polybutadiene compound were determined at a constant temperature of 32 C by a forced-vibration resonant mass type of apparatus. The constant thermal state of the elastomer was ensured by keeping the ambient temperature constant and by limiting the power dissipation in the specimen. Experiments were performed with both compression and shear specimens at several preloads (nominal strain varying from 0 to 5 percent), and the results are reported in terms of a complex stiffness as a function of frequency. Very weak frequency dependence is observed and a simple power law type of correlation is shown to represent the data well. Variations in the complex stiffness as a function of preload are also found to be small for both compression and shear specimens.

Gupta, P. K.↗