Structure formation of regenerated cellulose materials from NMMO-solutions

Polyvinyl alcohol: A review of research status and use of polyvinyl alcohol based nanocomposites

Initiation and completion of DNA replication defines the beginning and ending of S phase of the cell cycle. Successful progression through S phase requires that replication be properly regulated and monitored to ensure that the entire genome is duplicated exactly once, without errors, in a timely fashion. Given the immense size and complexity of eukaryotic genomes, this presents a significant challenge for the cell. As a result, DNA replication has evolved into a tightly regulated process involving the coordinated action of numerous factors that function in all phases of the cell cycle. We will review our current understanding of these processes from the formation of prereplicative complexes in preparation for S phase to the series of events that culminate in the loading of DNA polymerases during S phase. We will incorporate structural data from archaeal and bacterial replication proteins and discuss their implications for understanding the mechanism of action of their corresponding eukaryotic homologues. We will also describe the concept of replication licensing which protects against genomic instability by limiting initiation events to once per cell cycle. Lastly, we will review our knowledge of checkpoint pathways that maintain the integrity of stalled forks and relay defects in replication to the rest of the cell cycle.

/pdf/dna-replication-and-progression-through-s-phase-41r5txvdv5.pdf

DNA replication and progression through S phase

The most exciting advances in the tuberous sclerosis complex (TSC) field occurred in 1993 and 1997 with the cloning of the TSC2 and TSC1 genes, respectively, and in 2003 with the identification of Rheb as the target of tuberin's (TSC2) GTPase activating protein (GAP) domain. Rheb has a dual role: it activates mTOR and inactivates B-Raf. Activation of mTOR leads to increased protein synthesis through phosphorylation of p70S6K and 4E-BP1. Upon insulin or growth factor stimulation, tuberin is phosphorylated by several kinases, including AKT/PKB, thereby suppressing its GAP activity and activating mTOR. Phosphorylation of hamartin (TSC1) by CDK1 also negatively regulates the activity of the hamartin/tuberin complex. Despite these biochemical advances, exactly how mutations in TSC1 or TSC2 lead to the clinical manifestations of TSC is far from being understood. Two of the most unusual phenotypes in TSC are the apparent metastasis of benign cells carrying TSC1 and TSC2 mutations, resulting in pulmonary lymphangiomyomatosis, and the ability of cells with TSC1 or TSC2 mutations to differentiate into the separate components of renal angiomyolipomas (vessels, smooth muscle and fat). We will discuss how the TSC signaling pathways are affected by mutations in TSC1 or TSC2, focusing on how these mutations may lead to the renal and pulmonary manifestations of TSC.

Tuberous sclerosis complex: linking growth and energy signaling pathways with human disease

Synthesis, self-assembly and drug release behaviors of pH-responsive copolymers ethyl cellulose-graft-PDEAEMA through ATRP

In order to gain an understanding of the process of Lyocell fiber formation, the melting and solidification behaviors, heat capacity and density of cellulose N-methylmorpholine-N-oxide monohydrate (NMMO-MH) solutions were studied by differential scanning calorimetry (DSC) and dilatometry, and the diameter development of Lyocell fibers in the air gap was measured online. It was found that the Lyocell process can be considered as both a melt–spinning process in the air gap and a wet-spinning process in the coagulation bath. Cellulose chains in the solutions hindered the crystallization of NMMO-MH, and the melting point of the solutions decreased with increasing cellulose concentration. The density of cellulose NMMO-MH solutions decreased linearly with increasing temperature in the solid or the liquid state, and it increased with increasing cellulose concentration. The heat capacity of the solutions increased slightly with increasing temperature and concentration. The development of fiber diameter, the velocity gradient, and the gradient of the filaments in the air gap were limited to a short distance from the spinneret orifice. The position at which the velocity and the tensile stress gradient reached their maximum values moved closer to the spinneret orifice with increasing take-up speed.

An Analysis of Lyocell Fiber Formation as a Melt–spinning Process

The degree of polymerization (DP) and the molecular weight distribution (MWD) play a special role in producing cellulose fiber by using the N-methyl morpholine N-oxide (NMMO) process. In this paper, rheological methods have been used to determine the MWD of cellulose. It is shown that the limiting compliance J0e of cellulose samples increases strongly with the increasing broadness of MWD, and that the polydispersity index ‹τW›/‹τN› of the distribution of relaxation times can also well characterize the polydispersity of MWD of the cellulose samples. By using Tuminello's method, the cumulative weight distribution C(M) can be calculated from the terminal modulus and the plateau modulus of the cellulose/NMMO solution via 1-[G'(ω)/and G0N]0.5 (G'(ω) and G0N are the storage modulus and the plateau modulus respectively).

Xue-Chao Hu

Papers

An Analysis of Lyocell Fiber Formation as a Melt–spinning Process

Study on Molecular Weight Distribution of Cellulose by Using Rheological Methods