A statistical model of the dynamics of a mosquito vector (Culex tarsalis) population

A model of the dynamics of a mosquito Culex tarsalis is derived that includes the life states through which the mosquito proceeds. Transition probabilities from one state (egg, larva, pupa and adult) to another are derived and they depend on the duration of stay and mortality in each state. A formula is derived for the expected number of mosquitoes alive at any time during the spring or summer. This formula depends on the number of eggs oviposited and the transition probabilities. Data are used to estimate the parameters and to illustrate the usefulness of this model in examining the effect of changes in mosquito survival on the dynamics of the population.     

Preparation and etherification reaction of fatty dichlorocyclopropanes

Dichlorocarbene was added tocis-9-octadecene, methyl oleate, methyl elaidate, and methyl linoleate to form the corresponding mono- or bis-dichlorocyclopropanes in yields of 75–88%. The dichlorocyclopropanes underwent ring-opening substitution on heating with alcohols (or water) to form β-chlorallylic ethers (or alcohols). The ethers were obtained in yields of 46 to 84%. Tetraethylene glycol and methyl lactate, as hydroxyl compounds, gave a polyethenoxy ester and an ether-linked diester, respectively. Presented at AOCS meeting, Toronto, October, 1962. F. Utiliz. Res. & Dev. Div. ARS, U.S.D.A.     

The membrane affinities of the aliphatic amino acid side chains in an alpha-helical context are independent of membrane immersion depth

Understanding, predicting, and designing the binding of peptides and proteins to bilayers require quantifying the intrinsic propensities of individual amino acid residues to bind membranes as a function of structural context and bilayer depth. A host-guest study was performed using the peptide host named helix5 in order to determine the membrane affinities of the aliphatic side chains both in an alpha-helical context and as a function of bilayer depth. Use of the alpha-helical host with a constrained geometry allowed the placement of guest sites at three different depths in bilayers and minimized secondary structural changes due to guest substitutions. Circular dichroism and electron paramagnetic resonance (EPR) were used to characterize the aqueous and bilayer-bound structures of the peptide variants. EPR was also used to measure the bilayer-water partition constants of the peptide variants, and the Delta DeltaGtr values (relative to Gly) of the aliphatic amino acid side chains were subsequently calculated. Surprisingly, the DeltaDeltaGtr values did not significantly vary as a function of the guest site depth in bilayers. In addition, the Delta DeltaGtr values determined in an alpha-helical context are reduced to approximately two-thirds of Delta DeltaGtr values determined in other studies for the bilayer-water and octanol-water partitioning of amino acid side chains in extended and unstructured hosts. Both the relative reduction in Delta DeltaGtr values in the context of an alpha-helical host and the invariance of Delta DeltaGtr values with respect to bilayer depth are consistent with the membrane affinities of the aliphatic residues being largely determined by the classical hydrophobic effect.     

Fetal islet xenotransplantation in rodents and primates

(E)-2'-deoxy-2'-(fluoromethylene) cytidine (FMdC), a novel inhibitor of ribonucleotide-diphosphate reductase, has been shown to have anti-tumor activity against solid tumors and sensitize tumor cells to ionizing radiation. Pentoxifylline (PTX) can potentiate the cell killing induced by DNA-damaging agents through abrogation of DNA-damage-dependent G2 checkpoint. We investigated the cytotoxic, radiosensitizing and cell-cycle effects of FMdC and PTX in a human colon-cancer cell line WiDr. PTX at 0.25-1.0 mM enhanced the cytotoxicity of FMdC and lowered the IC50 of FMdC from 79 +/- 0.1 to 31.2 +/- 2.1 nM, as determined by MTT assay. Using clonogenic assay, pre-irradiation exposure of exponentially growing WiDr cells to 30 nM FMdC for 48 hr or post-irradiation to 0.5 to 1.0 mM PTX alone resulted in an increase in radiation-induced cytotoxicity. Moreover, there was a significant change of the radiosensitization if both drugs were combined as compared with the effect of either drug alone. Cell-cycle analysis showed that treatment with nanomolar FMdC resulted in S-phase accumulation and that such an S-phase arrest can be abrogated by PTX. Treatment with FMdC prior to radiation increased post-irradiation-induced G2 arrest, and such G2 accumulation was also abrogated by PTX. These results suggest that pharmacological abrogation of S and G2 checkpoints by PTX may provide an effective strategy for enhancing the cytotoxic and radiosensitizing effects of FMdC.     

Fatigue behaviour of synthetic fibres,yarns, and ropes

S-N fatigue and creep-rupture data have been obtained for nylon 6,6 single fibres, interlaced yarns, and small ropes under a variety of loading conditions. The results show a similar degradation rate at each level of structure, with no apparent influence of inter-fibre effects. Cyclic lifetimes of single fibres of nylon 6,6 as well as polyester and aramid can be predicted from a creep rupture model. Consistent with this model, the time to failure is insensitive to frequency over a broad range. For each level of structure the strain at failure is the same whether tested in simple tension or under cyclic or creep loading. Failure modes were generally similar in creep rupture and cyclic fatigue tests; no effect of a slack load on each cycle was evident either in the failure mode or specimen lifetime.     

Immobilization of acrylamide-modified oligonucleotides by co-polymerization

A flexible chemistry for solid phase attachment of oligonucleotides is described. Oligonucleotides bearing 5'-terminal acrylamide modifications efficiently co-polymerize with acrylamide monomers to form thermally stable DNA-containing polyacrylamide co-polymers. Co-polymerization attachment is specific for the terminal acrylamide group. Stable probe-containing layers are easily fabricated on supports bearing exposed acrylic groups, including plastic microtiter plates and silanized glass. Attachment can be accomplished using standard polyacrylamide gel recipes and polymerization techniques. Supports having a high surface density of hybridizable oligonucleotide (approximately 200 fmol/mm2) can be produced.     

The alloimmune thrombocytopenic syndromes

We have summarized five thrombocytopenic syndromes caused by platelet-reactive alloantibodies. Increased awareness of these five syndromes, together with the greater availability of highly-specialized laboratory methods to detect and to characterize platelet-reactive alloantibodies, will lead to their more frequent diagnosis. It is important for the clinician to consider unusual alloimmune thrombocytopenic disorders in clinical settings in which alloantigens that could be limited to just one family could cause important disease (ie, NAT caused by a private alloantigen; theoretically, PAT or TAT related to directed donations of blood or bone marrow). These considerations underscore the need for serological investigations to involve the family members rather than to rely on standard platelet typing donor pools.