ABSTRACT
Based on the results from UV-irradiated interstellar ice analogues, we describe a two-step phenomenological theory for enantiomer-selective, asymmetric formation of molecules like amino acid ...precursors: (1) UV photolysis of interstellar ices to molecular fragments/radicals and formation of racemic population of chiral molecules and (2) asymmetric photolysis of precursors by UV-circularly polarized light (UV-CPL), resulting in preferred growth of one enantiomer. Independent of specifics of step (1), when ice-analogue is irradiated with UV-CPL, enantiomeric excess of amino acids following hydrolysis is limited to |EEice(max)|=|(σ+ − σ−)/(σ+ + σ−)|, 0.5 times the anisotropy factor (g) for amino acid precursors (σ+/− is molecular cross-section for absorption of right/left UV-CPL light in cm2). For amino acids, the calculated EEice(max) ∼ 1 per cent agrees with experiments. Over small duration, EE is given by, |EEice(t)|=|(I+ − I−)(σ+ − σ−)|t/4, (I+/− is photon flux of right/left UV-CPL cm−2 s−1) which agrees with the observed dependence of EE on time-integrated flux of UV-CPL light. For ice irradiated with linearly polarized/unpolarized light followed by irradiation of residue with UV-CPL, |EEres(t)|=|tanh(I+ − I−)(σ+ − σ−)t/2| and can be much larger than EEice(max) for ice alone. When both ice and residue are irradiated with UV-CPL, EE = EEice + EEres and depends on the durations of irradiation for ice and residue. Similar analysis by assuming asymmetric photosynthesis of precursors as the underlying mechanism does not agree with experimental observations.
A novel blended solid polymer electrolyte comprising polyethylene oxide and polyvinylpyrrolidone polymers for blending and sodium nitrate (NaNO
3
) as ion conducting species has been optimized via ...standard solution-cast technique. XRD, FESEM, and FTIR were performed to obtain the information about the structural changes, morphology, and microstructural changes (polymer–ion and ion–ion interactions) of the solid polymer electrolyte films. The electrochemical impedance spectroscopy, linear sweep voltammetry, and
i
–
t
characteristics were performed to evaluate the ionic conductivity, voltage stability window, and ion transference number. The impedance study was done in a broad temperature range (40–100 °C). The DSC and TGA were used to obtain information about the thermal transitions and thermal stability of prepared films. The ion dynamics is further investigated by analyzing the complex permittivity, loss tangent, and complex conductivity. All the plots were fitted through established theoretical model/expressions in whole frequency window to obtain dielectric strength, ion conduction path behavior, and relaxation time. Transport parameters such as number density (
n
), mobility (
μ
), and diffusion coefficient (
D
) of mobile ions were obtained by three methods and compared satisfactorily. Lastly, a coherent mechanism for the migration of charge transport carriers within the solid polymer composites has been proposed based on the performed experimental outcome.
All-solid-state batteries are swiftly gaining the attention of the research community owing to their widespread applications in electric vehicles, digital electronics, portable appliances, etc. A ...battery comprises three components: cathode, anode and electrolyte. An electrolyte is the heart of the battery and plays a crucial role in the overall performance of the battery. In order to make the review more focused, all-solid-state Li-ion batteries (ASSLIBs) have been considered. This review covers the architecture of ASSLIBs, advantages, and characteristics of the solid polymer electrolytes. The important preparation methods are summarized, followed by the characterizations for testing the suitability of electrolytes for solid-state batteries. The discussion is focused on the ‘state of the art’ in the field of solid-state batteries, device fabrication, and comparison in terms of capacity, energy density, and cyclic stability. In the last section, the ion conduction mechanism in different solid polymer electrolytes is discussed. Finally, it is tried to give a possible outlook for developing future hybrid and multifunctional electrolytes which can act as a bridge for developing solid-state batteries covering a broad range of applications.
Some amino acids can crystallize from aqueous solution both as conglomerates and racemic compounds: under high supersaturation following rapid evaporation, dissolved amino acids draining over porous ...sand-bars behave like conglomerates whereas in the resulting deeper pool of water, amino acid solution switches to the more common racemic-compound system. We show how the two forms might have sequentially combined under prebiotic conditions to form the basis of homochirality. The paper is a quantitative analysis of enantiomeric excess (EE) this dual behavior of amino acids is capable of producing in tandem: Initial amplification by preferential crystallization (PC) in conglomerate system (CS) followed by further amplification in the racemic compound system (RCS). Using aspartic acid as a model system, ternary phase diagram shows that a minimum supersaturation of 1.65 is required in the CS for the solution-EE to reach its maximum value of 50% at the RCS eutectic point. A relationship is derived for the dependence of this threshold supersaturation on the eutectic solubilities of CS and RCS. For given supersaturation in CS, a relation is also derived for minimum solution-EE that must be produced by PC before CS switches to RCS. Required PC-induced threshold solution-EE of 0.194, 0.070, 0.033 is calculated for supersaturation of 2, 5, 10 respectively in aspartic acid. Switching from CS to RCS further amplifies solution-EE, resulting in an overall growth of aspartic acid solution EE from near-zero in CS to around 50% in RCS.
In the present article, we have studied the effect of the salt concentration (LiPF
6
) on transport properties and ion dynamics of blend solid polymer electrolyte (PEO–PAN) prepared by solution cast ...technique. Fourier transform infrared (FTIR) spectroscopy confirms the presence of microscopic interactions such as polymer–ion and ion–ion interaction evidenced by a change in peak area of anion stretching mode. The fraction of free anions and ion pairs obtained from the analysis of FTIR implies that both influence the ionic conductivity with different salt concentration. The complex dielectric permittivity, dielectric loss, complex conductivity have been analyzed and fitted in the entire frequency range (1 Hz–1 MHz) at room temperature. The addition of salt augments the enhancement of dielectric constant and shift of relaxation peak in loss tangent plot toward high frequency indicates a decrease of relaxation time. We have implemented the Sigma representation (σ″ vs. σ′) for solid lithium ion conducting films which provide better insight regarding the dispersion region in Cole–Cole plot (ε″ vs. ε′) in lower frequency window. The dielectric strength, relaxation time and hopping frequency are in correlation with the conductivity which reveals the authenticity of results. Finally, the ion transport mechanism was proposed for getting the better understanding of the ion migration in the polymer matrix.
While there is consensus that Archean atmosphere was anoxic with O
2
pressure,
p
(O
2
) <10
-6
PAL (present atmospheric level) at sea-level, evidence suggests that
p
(O
2
) at stratospheric altitudes ...of 10-50 km was orders of magnitude higher, a result of photodissociation of CO
2
by UVC sunlight and incomplete mixing of O
2
with other gases. Molecular O
2
is paramagnetic due to triplet ground state. Magnetic circular dichroism (MCD) by stratospheric O
2
is examined in earth’s magnetic field and shows maximum circular polarization │(
I
+
- I
-
)│ at altitude of 15-30 km (
I
+
/I
-
is intensity of left/right circularly polarized light). While (
I
+
- I
-
)/(
I
+
+ I
-
) is small (~10
-10
), it is an unexplored source of enantiomeric excess (EE) by asymmetric photolysis of amino acid precursors produced in volcanic eruptions. The precursors reside in stratosphere for periods of over a year due to relative absence of vertical transport. Due to negligible thermal gradient across equator, they are trapped in the hemisphere where they are produced, with interhemispheric exchange time of over a year. The precursors diffuse through altitudes of maximum circular polarization before getting hydrolyzed on ground to amino acids. Enantiomeric excess of ~10
-12
is calculated for precursors and amino acids. While small, this EE is orders of magnitude higher than predicted (~10
-18
) by parity violating energy differences (PVED) and could be the seed for growth of biological homochirality. Preferential crystallization (PC) is described as a plausible mechanism for amplification of solution EE of some amino acids from 10
-12
to 10
-2
, for period of several days.
Exponential increase in urbanization has led to a growing need for a mass rapid transit system in developing countries. Underground network of tunnels constructed using tunnel boring machines (TBMs) ...has been an efficient solution. Urban tunnels have an essential requirement of minimizing the ground disturbances as it adversely impacts the existing infrastructure. Current study presents potential correlations for parametric geotechnical assessment for mechanized soft ground tunnelling data considering statistical numerical regression. The established correlations essentially enable us to determine and validate the geotechnical parameters in real time and subsequently enables optimization and even potential automation of TBM operations during soft ground mechanized tunnelling.
Polymer electrolytes (PEs) are an essential component being used in most energy storage/conversion devices. The present review article on a brief history, advantage, and their brief application of ...polymer electrolyte systems. It consists of a glimpse on liquid, gel, and solid polymer electrolyte and a contrast comparison concerning benefits/disadvantages among the three. The article started with a brief introduction of polymer electrolytes followed by their varieties and extreme uses. The role of host polymer matrix by taking numerous examples of polymer electrolyte published by the different renowned group of the concerned field has been explored. The criteria for selection of appropriate host polymer, salt, inorganic filler/clay, and aprotic solvents to be used in polymer electrolyte have been discussed in detail. The mostly used polymer, salt, solvents, and inorganic filler/clay list has been prepared in order to keep the data bank at one place for new researchers. This article comprises different methodologies for the preparation of polymer electrolyte films. The different self-proposed mechanisms (like VTF, WLF, free volume theory, dispersed/intercalated mechanisms, etc.) have been discussed in order to explain the lithium ion conduction in polymer electrolyte systems. A numerous characterization techniques and their resulting analysis have been summarized from the different published reports at one place for better awareness of the scientific community/reader of the area.
A model-based description of the scaling and radial location of turbulent fluctuations in turbulent pipe flow is presented and used to illuminate the scaling behaviour of the very large scale ...motions. The model is derived by treating the nonlinearity in the perturbation equation (involving the Reynolds stress) as an unknown forcing, yielding a linear relationship between the velocity field response and this nonlinearity. We do not assume small perturbations. We examine propagating helical velocity response modes that are harmonic in the wall-parallel directions and in time, permitting comparison of our results to experimental data. The steady component of the velocity field that varies only in the wall-normal direction is identified as the turbulent mean profile. A singular value decomposition of the resolvent identifies the forcing shape that will lead to the largest velocity response at a given wavenumber–frequency combination. The hypothesis that these forcing shapes lead to response modes that will be dominant in turbulent pipe flow is tested by using physical arguments to constrain the range of wavenumbers and frequencies to those actually observed in experiments. An investigation of the most amplified velocity response at a given wavenumber–frequency combination reveals critical-layer-like behaviour reminiscent of the neutrally stable solutions of the Orr–Sommerfeld equation in linearly unstable flow. Two distinct regions in the flow where the influence of viscosity becomes important can be identified, namely wall layers that scale with R+1/2 and critical layers where the propagation velocity is equal to the local mean velocity, one of which scales with R+2/3 in pipe flow. This framework appears to be consistent with several scaling results in wall turbulence and reveals a mechanism by which the effects of viscosity can extend well beyond the immediate vicinity of the wall. The model reproduces inner scaling of the small scales near the wall and an approach to outer scaling in the flow interior. We use our analysis to make a first prediction that the appropriate scaling velocity for the very large scale motions is the centreline velocity, and show that this is in agreement with experimental results. Lastly, we interpret the wall modes as the motion required to meet the wall boundary condition, identifying the interaction between the critical and wall modes as a potential origin for an interaction between the large and small scales that has been observed in recent literature as an amplitude modulation of the near-wall turbulence by the very large scales.
PDF
