Delta Transition Research Articles

Genomic surveillance reveals early detection and transition of delta to omicron lineages of SARS-CoV-2 variants in wastewater treatment plants of Pune, India.

The COVID-19 pandemic has emphasized the urgency for rapid public health surveillance methods to detect and monitor the transmission of infectious diseases. The wastewater-based epidemiology (WBE) has emerged as a promising tool for proactive analysis and quantification of infectious pathogens within a population before clinical cases emerge. In the present study, we aimed to assess the trend and dynamics of SARS-CoV-2 variants using a longitudinal approach. Our objective included early detection and monitoring of these variants to enhance our understanding of their prevalence and potential impact. To achieve our goals, we conducted real-time quantitative polymerase chain reaction (RT-qPCR) and Illumina sequencing on 442 wastewater (WW) samples collected from 10 sewage treatment plants (STPs) in Pune city, India, spanning from November 2021 to April 2022. Our comprehensive analysis identified 426 distinct lineages representing 17 highly transmissible variants of SARS-CoV-2. Notably, fragments of Omicron variant were detected in WW samples prior to its first clinical detection in Botswana. Furthermore, we observed highly contagious sub-lineages of the Omicron variant, including BA.1 (~28%), BA.1.X (1.0-72%), BA.2 (1.0-18%), BA.2.X (1.0-97.4%) BA.2.12 (0.8-0.25%), BA.2.38 (0.8-1.0%), BA.2.75 (0.01-0.02%), BA.3 (0.09-6.3%), BA.4 (0.24-0.29%), and XBB (0.01-21.83%), with varying prevalence rates. Overall, the present study demonstrated the practicality of WBE in the early detection of SARS-CoV-2 variants, which could help track future outbreaks of SARS-CoV-2. Such approaches could be implicated in monitoring infectious agents before they appear in clinical cases.

Quadruple Hydrogen Bond-Containing A-AB-A Triblock Copolymers: Probing the Influence of Hydrogen Bonding in the Central Block.

This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of n-butyl acrylate (nBA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths.

The late Holocene Erin deflected and asymmetric wave-dominated delta – Puerto Grande Bay, Trinidad

The Erin modern marginal-marine depositional system sits along the Trinidad southwestern coastline. It is among the many unstudied and undocumented modern, dynamic coastal depositional systems around Trinidad. Our study defines the Erin system as being a deflected and asymmetric wave-dominated delta, and in so doing, elucidates the dynamics of the Erin system. This was done using a compendium of satellite images, temporal cross-shore elevation profiles, modern shallow sediment cores, and sediment samples.Geomorphologically, the Erin system comprises a vegetated delta plain and the unvegetated modern deposits. The delta plain has four amalgamated sand bars with intercalated lagoonal deposits. The unvegetated modern deposits is defined as the fifth bar of the system. These five bars were loosely correlated to the five 6th order eustatic cycles of the Holocene highstand. The modern, unvegetated deposit of the fifth bar is divided into an updrift segment and a downdrift segment relative to the inlet mouth. The updrift segment comprises a spit and beach depositional elements, while the downdrift segment comprises a barrier spit, back-barrier lagoon, rip-channels, and sometimes a bayhead delta at the Erin River mouth. The dynamic, annual evolution of the spit reflects a seasonally controlled, possibly cyclical evolution wherein the delta transitions from being asymmetric to deflected-asymmetric. This phenomenon is postulated to be brought on by seasonal changes in the wave regime, and not, as one might expect, seasonally controlled river discharge. That is, during the summer wave season, when net-deposition occurs, the system morphology is deflected as a consequence of increase sedimentation in the nearshore. During the winter wave season, when net-erosion is expected, the system morphology reflects that of a typical asymmetric delta, as a consequence of reduced sedimentation in the nearshore. This cyclical movement of sediment is also observed in cross-shore elevation profiles.Sedimentologically, six depositional elements were sampled using sediment cores: foreshore, updrift spit, channel bars, mouth bar, barrier spit (downdrift), and back-barrier lagoon. Physical sedimentary structures reflected wave energy dominance across the system with an increase in tidal signatures within the lagoon deposits and lower foreshores. Biogenic sedimentary structures were limited across much of the system, but the traces recorded were mostly isolated in the downdrift back-barrier lagoon deposits, and few in the upper barrier spit. Grainsize distributions showed an average grainsize of fine sand across the system with coarse-grained, poorly sorted, bio-clastic sands present as channel lag deposits. An increase in mud content was recorded in the downdrift segment of the delta. The geomorphological, sedimentological, and ichnological data described above provided sufficient evidence to define the Erin system as an asymmetric wave-dominated delta with seasonally controlled deflected morphology.

Sedimentary evolution and controlling factors of Early-Mid Miocene Deltaic systems in the Northern Pearl River Mouth Basin, South China Sea

The Pearl River Mouth Basin is located at the northern continental shelf of the South China Sea. Since the early Miocene, the Paleo-pearl river transported a large amount of sediments to the northwest of the basin and resulted in the formation of a large-scale river-delta depositional system, which has become an important oil and gas reservoir in the study area. In the current paper, we investigate the characteristics and evolution of fluvial-deltaic depositional systems and their controlling factors, including sea level change, tectonic subsidence and sediment supply on the basis of 3D seismic, well logging and core data. Early-Mid Miocene succession can be divided into two second-order sequences (CS1–CS2) and eight third-order sequences (S1–S8). Deltaic systems developed in S1–S2 are relatively coarse in grain size, and the delta plain deposits are dominated by thickly stacked (100–180 m) distributary channel sand bodies and interpreted as braided delta depositional system. In the early stage (S1–S2), the braided delta systems mainly distributed in the west of the Baiyun Sag, which were proceeded by a retreat to the south of the Enping Sag along with sharply rising sea level. Following the transgression of S2, the provenance of the Paleo-Pearl River extended to the coastal region of South China, and the papleoclimate changed from warm and humid to dry and cold in the early Miocene, leading to the development of transition of braided river delta to meandering river delta, which was characterized by relatively fine grain deposits. During the deposition of S3–S6, well sorted and rounded fine sandstones of deltaic front deposits accumulated in the study area. The retrogradation to accretion and subsequent progradation of these meander delta systems are attributed to the sea level change in the study area. During the deposition of S7–S8, the delta front retreated to the south of the Enping depression as a result of minor sea level rise, reduction in sediment input, and subsidence rate. This resulted in the development of a wave-controlled deltaic depositional system.

Electromagnetic transition form factors, E2/M1 and C2/M1 ratios of the baryon decuplet

We investigate the electromagnetic transition form factors of the baryon decuplet to the baryon octet, based on the self-consistent SU(3) chiral quark-soliton model, taking into account the effects of explicit breaking of flavor SU(3) symmetry. We emphasize the Q^2 dependence of the electromagnetic Nrightarrow Delta transition form factors and the ratios of E2/M1 and C2/M1 in comparison with the experimental and empirical data. In order to compare the present results of the electromagnetic transition form factors of the Nrightarrow Delta with those from lattice QCD, we evaluate the form factors with the pion mass deviated from its physical value. The results of the E2/M1 and C2/M1 ratios are in good agreement with the lattice data. We also present the results of the electromagnetic transition form factors for the decuplet to the octet transitions.

Sedimentary transition of the Yangtze subaqueous delta during the past century: Inspiration for delta response to future decline of sediment supply

How the Yangtze delta responds to riverine sediment decline has become a hot research topic and an urgent issue to be addressed, especially after the impoundment of the Three Gorges Dam in 2003. This study investigated sedimentary features through the sediment granularity of surficial samples and short cores over the entire Yangtze subaqueous delta, aiming to better understand the spatial response of the subaqueous delta to sediment supply decline and local hydrodynamic adjustment of the estuary. The results show that four sedimentary zones of estuarine sand bar (Zone I), prodelta (Zone II), delta-shelf transition zone (Zone III) and residual sand (Zone IV) are distributed from the estuary to the shelf, characterised by first fining from zone I to zone II, and then coarsening from zone II to zone IV on grain size of surficial sediments. In the past few hundred years, the subaqueous delta has been generally prograded seaward following this sedimentary system spatially, manifested by generally fining upwards in the cores of the main subaqueous delta. However, sediment coarsening occurs on the top of the cores in the delta-shelf transition zone (Zone III), implying a recent retrogradation process. Based on the results of 210Pb and 137Cs, the sedimentary transition from progradation to retrogradation occurred since 1950s and was intensified after 1980s in the north part of Zone III, mainly caused by channel shrinking of the North Branch and riverine sediment decline. Comparatively, such a sedimentary transition is not significant in the south part of Zone III. But it is worth noting that surficial coarsening in the core (of the south part of Zone III) is probably related to drastic sediment decline since 2003 when the Three-Gorges Dam closed, which means that the Yangtze subaqueous delta has probably been in a full sedimentary transition. The sedimentary transition of the north subaqueous delta can provide an insightful reference for the sedimentary response of the Yangtze delta to further decline of sediment supply in the future.

A river-dominated to tide-dominated delta transition: A depositional system case study in the Orinoco heavy oil belt, Eastern Venezuelan Basin

The Orinoco heavy oil belt (OHOB), which has the most significant heavy oil reserve in the world, has shown various sedimentary patterns and different evolution processes within its different blocks. We selected two blocks, Junin in the west and Carabobo in the east, to analyze the depositional environment distinctions due to different transgression processes. Based on the interpretation of 3D seismic data and electrical well-logging facies and analysis of depositional phenomena using cores, we clarified diverse depositional associations and constructed a sedimentary evolution model of the depositional system in the study area. We suggest that the depositional system transitioned from a braided river delta to a tide-dominated delta in the Early Miocene and that two factors mainly controlled the transition: paleo-flow and paleo-geomorphology, which are related to tectonic uplift and transgression processes. Transgression increased gradually through tectonic activity, though transgression rates varied area to area, resulting in different depositional environment transitions and sand-body distribution patterns. In the Carabobo block (east), a gentle slope developed, indicating a fast transgression rate. The intense interaction between river and tide flow led to a large inter-distributary channel area with high-sinuosity- or tidal-channels (relative to the Junin block). In the Junin block (west), tectonic activity developed a large accommodation area providing space for the sediment produced, slowing the transgression rate, and contributing to a mainly fluvial delta environment. Due to the gradual intensive transgression, channel stack patterns transitioned from braided-to meandering-channel in the river dominated delta or tidal-channel in the tide-dominated delta.

Thermal, Abrasion and Dynamic-Mechanical Properties of Sugar Cane Bagasse Reinforced Polyester Resin Biocomposites

Biodegradable composites (SCB-PES) and a control sample were developed from polyester resin (PES) matrix and sugar cane bagasse (SCB) fibre at different matrix- fibre compositions using the compression technique. The effects of fibre content (9–54 wt%) and fibre treatment on thermal and dynamic mechanical properties of polyester / sugar cane bagasse fibre biocomposites were evaluated via thermogravimetric analysis (TGA) and DMA (Model: DMA 242 E Artemis) storage modulus (E1), loss modulus (E11), change in length of modulus (∆l), tan delta (E11/ E1) and glass transition temperature (Tg). The results showed that while the weight of the pure PES matrix showed a near complete disappearance between 400 –500 0C, the 9 % FW SCB-PES composite lost nearly 50% of its weight, in the same temperature region. The results which show that SCB-PES composites demonstrated acceptable thermal and abrasion properties portrays the effectiveness of SCB as reinforcement for PES matrix and the potential of the eco-friendly composites in the fabrication of utility materials for sustainable development. The weight loss (wt%) by the composites after 6 months soil burying test ranged from 22.24 -85.34 %.

Data Compression via Low Complexity Delta Transition Lossless Encoding for Remote Physiological and Environmental Monitoring.

Continuous remote physiologic and environmental monitoring, employing an ever-increasing array of sensors, is now commonplace. Given the significant amount of data being digitized, two common sources of energy consumption can be targeted to improve device runtime: data storage and data transmission. One embedded method to maximize device runtime is inline low energy data compression. Herein we present a low complexity data encoding scheme. We list and characterize the parameters necessary for encoding. The encoding method is then evaluated and tuned using contrived data with varying degrees of covariance, as well as open-source electrocardiography (ECG) data. Finally, the encoding method is evaluated with tri-axial accelerometry and ECG data previously collected on a Mount Everest Expedition using a remote physiologic monitor that was specifically designed for long autonomous runtimes. With the described low overhead delta transition lossless encoding method, the Mt. Everest device runtime would have doubled from two to four weeks of continuous recording. Finally, this approach would be beneficial given a requirement to transmit data wirelessly in real time, since the total transmission power and energy would be reduced by an amount related to the compression ratio.

Recent coarsening of sediments on the southern Yangtze subaqueous delta front: A response to river damming

After more than 50,000 dams were built in the Yangtze basin, especially the Three Gorges Dam (TGD) in 2003, the sediment discharge to the East China Sea decreased from 470 Mt/yr before dams to the current level of ~140 Mt/yr. The delta sediment's response to this decline has interested many researchers. Based on a dataset of repeated samplings at 44 stations in this study, we compared the surficial sediment grain sizes in the southern Yangtze subaqueous delta front for two periods: pre-TGD (1982) and post-TGD (2012). External factors of the Yangtze River, including water discharge, sediment discharge and suspended sediment grain size, were analysed, as well as wind speed, tidal range and wave height of the coastal ocean. We found that the average median size of the sediments in the delta front coarsened from 8.0 µm in 1982 to 15.4 µm in 2012. This coarsening was accompanied by a decrease of clay components, better sorting and more positive skewness. Moreover, the delta morphology in the study area changed from an overall accretion of 1.0 cm/yr to an erosion of − 0.6 cm/yr. At the same time, the riverine sediment discharge decreased by 70%, and the riverine suspended sediment grain size increased from 8.4 µm to 10.5 µm. The annual wind speed and wave height slightly increased by 2% and 3%, respectively, and the tidal range showed no change trend. Considering the increased wind speed and wave height, there was no evidence that the capability of the China Coastal Current to transport sediment southward has declined in recent years. The sediment coarsening in the Yangtze delta front was thus mainly attributed to the delta's transition from accumulation to erosion which was originally generated by river damming. These findings have important implications for sediment change in many large deltaic systems due to worldwide human impacts.

Facies transition and depositional architecture of the Late Eocene tide-dominated delta in northern coast of Birket Qarun, Fayum, Egypt

Late Eocene successions in the Fayum Depression display notable facies transition from open-marine to brackish-marine realms. Stratigraphic and sedimentologic characteristics of the depositional facies are integrated with ichnological data for the recognition of four facies associations (FA1 to FA4). The transition from open-marine sandstones (FA1) to the brackish-marine deposits (FA2) heralds a transgressive – regressive dislocation. The shallowing- and coarsening-upward progradation from the basal prodelta mudstone-dominated facies (FA2a) to deltafront heterolithics (FA2b) and sandstone facies (FA2c) are overlain by finning-upward delta plain deposits which are expressed by the delta plain mudstone (FA2d) and erosive-based distributary channel fills (FA4). Prodelta/deltfront deposits of FA2 are arranged in thinning- and coarsening-upward parasequences which are stacked in a shallowing-upward progressive cycle. Shallow-marine fossiliferous sandstones (FA3) mark the basal part of each parasequence. Stratigraphic and depositional architectures reflect a tide-dominated delta rather than an estuarine and incised valley (IV) model. This can be evinced by the progressive facies architecture, absence of basal regional incision or a subaerial unconformity and the stratigraphic position above a maximum flooding surface (MFS), in addition to the presence of multiple tidally-influenced distributary channels. Stratigraphic and depositional characteristics of the suggested model resemble those of modern tide-dominated deltaic systems. Accordingly, this model contributes to our understanding of the depositional models for analogous brackish-marine environments, particularly tide-dominated deltas in the rock record.

Influence of light-activation protocol on methacrylate resin-composite evaluated by dynamic mechanical analysis and degree of conversion.

The aim of this study was to evaluate the degree of conversion (DC) and to identify the viscoelastic properties: storage modulus (E'), loss modulus (E"), tangent delta (tan δ), and glass transition temperature (T g ) of a microhybrid resin-composite light-activated by three different protocols. A Filtek Z250 (3 M ESPE) shade A3 was inserted in a Teflon mold (21 mm × 5 mm × 1 mm for viscoelastic properties; and 5 mm × 1 mm for DC) and light-activated according to the following light-activation protocols: (S) 1,000 mW/cm(2) × 19 s, (HP) 1,400 mW/cm(2) × 14 s, and (PE) 3,200 mW/cm(2) × 6 s, all set up to deliver 19 J/cm(2). Viscoelastic properties was assessed by dynamic mechanical analysis (DMA) (n = 3), performed in single cantilever clamped mode. DC (n = 5) was measured by FTIR on top (T) and bottom (B) surfaces, and the data was submitted to a split-plot one-way ANOVA. For DC, there was a significant effect for surface factor and light-activation protocols factor. Top surface showed higher DC than B in all experimental conditions. Light-activation protocols S and HP resulted in higher DC than PE and were similar between them. Viscoelastic properties (E', E", tan δ, T g ) were not affected by light-activation protocols. It could be concluded that light-activation protocols influenced DC but not influenced the viscoelastic properties.

Elastic and Transition Form Factors of the Δ(1232)

Predictions obtained with a confining, symmetry-preserving treatment of a vector-vector contact interaction at leading-order in a widely used truncation of QCD's Dyson-Schwinger equations are presented for \Delta and \Omega baryon elastic form factors and the \gamma N -> \Delta transition form factors. This simple framework produces results that are practically indistinguishable from the best otherwise available, an outcome which highlights that the key to describing many features of baryons and unifying them with the properties of mesons is a veracious expression of dynamical chiral symmetry breaking in the hadron bound-state problem. The following specific results are of particular interest. The \Delta elastic form factors are very sensitive to m_\Delta. Hence, given that the parameters which define extant simulations of lattice-regularised QCD produce \Delta-resonance masses that are very large, the form factors obtained therewith are a poor guide to properties of the \Delta(1232). Considering the \Delta-baryon's quadrupole moment, whilst all computations produce a negative value, the conflict between theoretical predictions entails that it is currently impossible to reach a sound conclusion on the nature of the \Delta-baryon's deformation in the infinite momentum frame. Results for analogous properties of the \Omega baryon are less contentious. In connection with the N->\Delta transition, the Ash-convention magnetic transition form factor falls faster than the neutron's magnetic form factor and nonzero values for the associated quadrupole ratios reveal the impact of quark orbital angular momentum within the nucleon and \Delta; and, furthermore, these quadrupole ratios do slowly approach their anticipated asymptotic limits.

Insights into theγ*N→Δtransition

The \gamma* N -> \Delta(1232) transition is a window on hadron shape deformation, the applicability of perturbative QCD at moderate momentum transfers, and the influence of nonperturbative phenomena on hadronic observables. We explain that the Ash-convention magnetic transition form factor must fall faster than the neutron's magnetic form factor and nonzero values for the associated quadrupole ratios reveal the impact of quark orbital angular momentum within the nucleon and \Delta(1232); and show that these quadrupole ratios do approach their predicted asymptotic limits, albeit slowly.

Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta

Over the last half century, while the total sediment load of the Danube dramatically decreased due to dam construction on tributaries and its main stem, a grand experiment was inadvertently run in the Danube delta: the construction of a dense network of canals, which almost tripled the water discharge toward the interior of the delta plain. We use core-based and chart-based sedimentation rates and patterns to explore the delta transition from the natural to an anthropogenic regime, to understand the effects of far-field damming and near-field channelization, and to construct a conceptual model for delta development as a function sediment partition between the delta plain and the delta coastal fringe. We show that sediment fluxes increased to the delta plain due to channelization counteracting sea level rise. In turn, the delta coastal fringe was most impacted by the Danube's sediment load collapse. Furthermore, we suggest that morphodynamic feedbacks at the river mouth are crucial in trapping sediment near the coast and constructing wave-dominated deltas or lobes. Finally, we suggest that increased channelization that mimics and enhances natural processes may provide a simple solution for keeping other delta plains above sea level and that abandonment of wave-dominated lobes may be the most long term efficient solution for protecting the internal fluvial regions of deltas and provide new coastal growth downcoast.

Analysis on Grain-Size Characteristics and Sedimentary Environment of Conglomerate Reservoirs in Ying-4 Section of Xingcheng Gas Field of Songliao Basin

Aimed at difficulty of conglomerate in Ying-4 Section of Xingcheng Gas Field, Songliao Basin, which it is impossible to be carried out, using routine granularity analysis methods, and the iconic grain-size analysis is carried out. According to iconic two-dimension grain-size analysis, and contacting to fundamental sedimentary characteristics of conglomerate, sedimentary environment analysis is carried out. It is thought that this area is Shallow gravel-bed braided fluvial fan deltas, to braided fluvial delta transition, which supported an important geological foundation for the next disposition of exploration in Xingcheng Gas Field.

Initiation of the Changjiang (Yangtze) delta and its response to the mid-Holocene sea level change

The Changjiang (Yangtze) delta in eastern China is one of the largest tide-dominated deltas in the world. To obtain a more detailed information on its initiation, we drilled three sediment cores, PK01, HG01 and XJ03, from the uppermost region of the delta plain. On the basis of sedimentary facies and AMS 14C dating, we identified three depositional systems: (1) a fluvial system, (2) an estuarine system, and (3) a deltaic system including an initial delta (estuary–delta transition) and a typical delta. The maximum flooding surface separates the estuarine and deltaic systems and occurred at ca. 8.0calkyr BP, when brackish water intruded landward and reached the Nanjing area. The Changjiang delta was initiated at the area between Nanjing and Yizheng when the sea-level rise decelerated after the rapid rise in sea level during 9.0–8.2calkyr BP.The subsequent evolution of the Changjiang delta has been shown as a seaward development model of river-mouth bars with shoreline migration. The oldest river-mouth bar called Hongqiao sand body, which is located most landward, was dated at 6.0–5.5calkyr BP in this study, nearly one thousand years younger than the previous estimates. A tide-dominated, funnel-shaped estuary was formed at 8.0calkyr BP, and lasted until the Hongqiao sand bar became exposed. This stage is regarded as an aggradation-dominated initial stage of the Changjiang delta, followed by a progradation-dominated stage that is characterized by the formation of a series of seaward migrating river-mouth bars. A relative sea level highstand in the mid-Holocene may be associated with glacio-hydro-isostatic tilting.

Writer Field Gradient Measurement on Spinstand

The gradient of magnetic head field is very critical in the writing process and it is one of the key factors to determine the achievable linear density of magnetic recording system. This work proposed a new method to measure the writer field gradient on Spinstand. The even harmonic ripple effect [4] is used to produce the modulated magnetostatic field at the writing transitions generated from the old data pattern at leading edge side of the writer. The newly written single tone signals have the modulated transition shift. Through the duty cycle measurement of the single tone signals, the delta transition shift can be measured. With the calculated magnetostatic field based on the media magnetic properties and the measured size of writer footprint, the writer field gradient equals the ratio of delta magnetostatic field over delta transition shift.

Prediction of Storage Life of Propellants having Different Burning Rates using Dynamic Mechanical Analysis

Propellants, visco-elastic in nature, show time and temperature dependent behaviour on deformation. Hence, the time–temperature superposition principle may be applied to the visco-elastic properties of propellants. In the present study, dynamic mechanical analyser (DMA) was used to evaluate the dynamic mechanical properties and quantify the storage life of four different propellants based on hydroxyl terminated polybutadiene, aluminium and ammonium perchlorate having different burning rates ranging from 5 mm/s to 25 mm/s. Each sample was given a multi-frequency strain of 0.01 per cent at three discrete frequencies (3.5 Hz, 11 Hz, 35 Hz) in the temperature range - 80 °C to + 80 °C. The storage modulus, loss modulus, tan delta and glass transition temperature (Tg) for each propellant samples have been evaluated and it is observed that all the propellants have shown time (frequency) and temperature dependent behaviour on deformation. A comparison of the log aT versus temperature curves (where aT is horizontal (or time) shift factor) for all four propellants indicate conformance to the Williams–Landel–Ferry (WLF) equation. The master curves of storage modulus (log E versus log ω plots) were generated for each propellant. A plot of E versus time for all propellants was generated up to 3 years, 6 years, and 10 years of time, respectively. The drop in the storage modulus below the acceptable limit with time may be used to predict the shelf life of the propellant. Defence Science Journal, 2012, 62(5), pp.290-294 , DOI:http://dx.doi.org/10.14429/dsj.62.2480

On the formation mechanism of UZr 2 phase

Intermetallic delta phase (UZr 2) in U–Zr alloy system is known to have hexagonal crystal structure. However, the formation mechanism of delta phase from the parent bcc gamma phase was not investigated before. With an extensive XRD analysis along with the microhardness data the present investigation reveals that gamma to delta transition takes place by the mechanism of omega transformation. Formation of both athermal and isothermal delta phase is also established for UZr 2 alloy composition.