Crystal nucleation mechanism in melts of short polymer chains under quiescent conditions and under shear flow

We present a molecular dynamics simulation study of crystal nucleation from undercooled melts of n-alkanes, and we identify the molecular mechanism of homogeneous crystal nucleation under quiescent conditions and under shear flow. We compare results for n-eicosane(C20) and n-pentacontahectane(C150), i.e. one system below the entanglement length and one above. Under quiescent conditions, we observe that entanglement does not have an effect on the nucleation mechanism. For both chain lengths, the chains first align and then straighten locally. Then the local density increases and finally positional ordering sets in. At low shear rates the nucleation mechanism is the same as under quiescent conditions, while at high shear rates the chains align and straighten at the same time. We report on the effects of shear rate and temperature on the nucleation rates and estimate the critical shear rates, beyond which the nucleation rates increase with the shear rate. We show that the viscosity of the system is not affected by the crystalline nuclei.Comment: 9 page

The Early Crystal Nucleation Process in Hard Spheres shows Synchronised Ordering and Densification

We investigate the early part of the crystal nucleation process in the hard sphere fluid using data produced by computer simulation. We find that hexagonal order manifests continuously in the overcompressed liquid, beginning approximately one diffusion time before the appearance of the first `solid-like' particle of the nucleating cluster, and that a collective influx of particles towards the nucleation site occurs simultaneously to the ordering process: the density increases leading to nucleation are generated by the same individual particle displacements as the increases in order. We rule out the presence of qualitative differences in the early nucleation process between medium and low overcompressions, and also provide evidence against any separation of translational and orientational order on the relevant lengthscales

Nonlinear shear of entangled polymers from nonequilibrium molecular dynamics

This work aims to improve the use of Molecular Dynamics simulations of Kremer-Grest chains to inform future developments of models of entangled polymer dynamics. We perform non-equilibrium molecular dynamics simulations, under shear flow, for well entangled Kremer-Grest chains. We study chains of 512 and 1000 Kremer-Grest beads, corresponding to 8 and 15 entanglements, respectively. We computed the linear rheological properties from equilibrium simulations of the stress auto-correlation function and obtained from these data the tube model parameters. Under non-linear shear flow, we compute the shear viscosity, the first and second normal stress differences and chain contour length. For chains of 512 monomers we obtain agreement with the shear stress results of Cao and Likhtman [ACS Macro Letters (2015) vol. 4 (12) pp. 1376-1381]. We also compare our non-linear results for both chain lengths with the GLaMM model, a widely used non-linear tube model. We identify some systematic disagreement that becomes larger for the longer chains. We made a systematic comparison of the transient shear stress maximum from our simulations, two non-linear models and experiments on a wide range of both melts and solutions, including polystyrene, polybu-tadiene and styrene-butadiene rubber. This comparison establishes that the polystyrene melt data show markedly different behaviour to all other melts and solutions and that Kremer-Grest simulations reproduce the polystyrene data more closely than either the GLaMM or Xie and Schweizer models. We also discuss the performance of these two models against the data and simulations. Finally, by imposing a rapid reversing flow, we produce a method to extract the recoverable strain from MD simulations, valid for sufficiently entangled monodisperse polymers. We then explore how the resulting data can be used to probe the melt state just before the reversing flow

Wireless sensor network for landslide monitoring

E very year all over the world many lives and properties are lost due to many geological catastrophes like, landslide or landslip. Manual and electronic monitoring systems are used for predicting the landslide. The m anual monitoring syst em is laborious and not practical. And most of the electronic systems are complex and expensive. A wireless sensor network in conjunction with a n underground pretension cable with a strain gage sensor attached at one end is proposed for a simple landslide monitoring system . A mathematical model has been developed for the system and the model is verified by simulation. The result shows that an early prediction of the landslide is possible by using the developed system

Types of Non-Acute Headache and Neuroimaging in the Evaluation of Patients with this Type of Headache

The aim of this study was to find the type of non-acute headache and to estimate the frequency of significant intracranial lesions in this type of headache. Non-acute headache was defined as any type of headache that had begun at least four weeks before. All the patients aged > 15 years attending the neurology and neurosurgery clinics of Post Graduate Medical Institute (PGMI), Lady Reading Hospital (LRH) Peshawar with non-acute headache were included in the study. The pregnant women and patients with facial pain alone were excluded from the study. They were followed prospectively for over a year. Detailed history and through neurlogic exami-nation was performed. The headache was classified according to the International Classification of Headache Disorder (ICHD) second edition of the International Headache Society (IHS). Every patient was investigated by neuroimaging studies. The computed tomography (CT) was done in all patients. Magnetic resonance imaging (MRI) was done in 86 patients to improve their diagnosis. Neuroimaging results were classified as “significant abnormalities”, “non-significant abnormalities” or “normal”. Significant abnormalities included neoplastic disease, hydrocephalus, vascular malformations, chiari malformation, large aracnoid cysts, intracranial hemorrhage and acute cerebral infarcts. The total number of patients was 1200; 795 women and 405 men. Their mean age was 38 years (15-75 years). Neuroimaging studies detected significant lesions in 18 patients (1.5%). The proportion of patients with headache and intracranial lesions is relatively small but neither neurological examination nor the features in the clinical history permit us to rule out such abnormalities

Biogeographical patterns in soil bacterial communities across the Arctic region

The considerable microbial diversity of soils and key role in biogeochemical cycling have led to growing interest in their global distribution and the impact that environmental change might have at the regional level. In the broadest study of Arctic soil bacterial communities to date, we used high-throughput DNA sequencing to investigate the bacterial diversity from 200 independent Arctic soil samples from 43 sites. We quantified the impact of spatial and environmental factors on bacterial community structure using variation partitioning analysis, illustrating a nonrandom distribution across the region. pH was confirmed as the key environmental driver structuring Arctic soil bacterial communities, while total organic carbon (TOC), moisture and conductivity were shown to have little effect. Specialist taxa were more abundant in acidic and alkaline soils while generalist taxa were more abundant in acidoneutral soils. Of the 48 147 bacterial taxa, a core microbiome composed of only 13 taxa that were ubiquitously distributed and present within 95% of samples was identified, illustrating the high potential for endemism in the region. Overall, our results demonstrate the importance of spatial and edaphic factors on the structure of Arctic soil bacterial communities

Studies on antihyperlipidemic and endothelium modulatory activities of polyherbal formulation (POL4) and its ingredients in high fat diet-fed rats

A compound herbal formulation (POL4) is used traditionally in interior parts (Distt. Badin) of Sindh, Pakistan, for the treatment of metabolic disorders like diabetes and hyperlipidemia. This study is aimed to determine the effectiveness of POL4 and its ingredients in hyperlipidemia and associated endothelial dysfunction and hypertension. POL4 is composed of equal proportion of Nigella sativa, Cichorium intybus, Trigonella foenum graecum and Gymnema sylvestre mixed in powdered form. Chronic (6 to 7 weeks) administration of POL4 and its ingredients mixed in diet caused a notable attenuation in total cholesterol, low density lipoprotein cholesterol, triglycerides, atherogenic index, C-reactive protein and glucose, while it has increased high density lipoprotein levels. POL4 intervention markedly (p\u3c0.01) reduced systolic blood pressure in rats to 127±1.92 vs. 145.4±1.07 mm of Hg using tail-cuff method and significantly (p\u3c0.05) improved endothelium-dependent relaxation (75±2.88 vs. 82.75±1.22%) to acetylcholine in isolated aortae of rats in treatment groups using force transducer and PowerLab system. Similar activities were assessed on the part of ingredients of POL4. These findings indicate that POL4 and its ingredients possess antihyperlipidemic, endothelium-dependent modulatory and antihypertensive activities, thus providing an evidence to the vernacular use of POL4 in hyperlipidemia and hypertension

Direct observation of long chain enrichment in flow-induced nuclei from molecular dynamics simulations of bimodal blends

Modelling of flow-induced nucleation in polymers suggest that long chains are enriched in nuclei, relative to their melt concentration. This enrichment has important consequences for the nucle-ation rate and mechanism, but cannot be directly observed with current experimental techniques. Instead, we ran united atom molecular dynamics simulations of bimodal polyethylene blends, comprising linear chains at a 50:50 mix of long (1000 carbon) and short (500-125 carbon) chains, under shear flow. We developed a method to extract the nucleus composition during a transient start-up flow. Our simulations show significant and systematic enrichment of long-chains for all nucleus sizes up to and beyond the critical nucleus. This enrichment is quantitatively predicted by the recent polySTRAND model [Read et al. Phys. Rev. Lett. 2020, 124,147802]. The same model parameters also correctly capture the nucleus induction time in our simulations. All parameters of the model were fitted to a small subset of our data in which long chain enhancement was absent. We conclude that long-chain enrichment is central to the mechanism of flow-induced nucleation and that this enrichment must be captured to correctly predict the nucleation rate

Poverty Condition of Lipa’ Saqbe Mandar Weavers: Initial Findings from Agriculture Area of West Sulawesi, Indonesia

Lipa' Saqbe Mandar (or just called Lipa' saqbe) is an unique culture of Mandar ethnic, it is still preserved today, because the Mandar people wear Lipa' Saqbe at every event held both in traditional ceremonies of Mandar culture like weddings or grief moments. Lipa' Saqbe weavers are the majority of mandarist fishermen and the wives of the peasants who in the concept of indigenous culture mandar adheres to the principle of Siwali Parriq which means the wives of Mandar descendants are able to work to help the family economy, one of them by weaving. This paper attempst to calculate weavers household who are living below poverty line and how severe they are? The study employed Foster- Greer-Torbecke (FGT) Indices Method: Head Count Index (HCI) and Poverty Gap Index (PGI). The results show that: (1) HCI of the study is 0.7333 indicate that 70.33% of Lipa' Saqbe weaver is living below poverty line, while (2) PGI reveals that the depth of poverty in weaver household is, however, close to zero (0) indicating that no poverty severity gap among households. The low income of Mandar silk weavers is the marketing system through traders or distributors. Although most of the weavers sell their woven products directly to the local market, the purchasing power of local communities is quite low so that their woven products are sold to wholesalers or distributors