bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of compatibilizer on the co‐continuity and nanoclay dispersion level of tpe nanocomposites based on PP/EPDM
Authors: Mirzadeh Amin , Lafleur Pierre G. , Kamal Musa R. , Dubois Charles
Published: June 2010

The effects of different polypropylene (PP)‐g‐maleic anhydride polymers, used as compatibilizers, on the degree of exfoliation and co‐continuity of PP/ethylene‐propylene‐diene terpolymer (EPDM) thermoplastic elastomer (TPE)/clay nanocomposites were investigated. X‐ray diffraction and transmission electron microscopic micrographs showed that nanocomposites ranged from intercalated structure to a coexistence of intercalated tactoids and exfoliated layers. The observed significant increase in crystallization temperature (∼20°C) could be beneficial for molding applications, because it means faster solidification and shorter cycle time. The rheological characteristic relaxation time of the compatibilizer correlated with the dispersion level in the nanocomposites. Solvent extraction and gravimetry measurements of continuity showed that compatibilizer affects the co‐continuity composition range through its effect on the dispersion level of nanoclays. At high EPDM concentration, the continuity of the thermoplastic phase for semi‐exfoliated TPE nanocomposites was higher than in the corresponding TPEs. Considering that TPE formation is the first step for thermoplastic vulcanizate production, where the thermoplastic phase should have a certain level of continuity, these results suggest that higher levels of EPDM could be incorporated into the semi‐exfoliated system before losing matrix continuity. It was also observed that there is a direct relation between the magnitude of the normalized stress growth viscosity overshoot and the continuity of TPE nanocomposites. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers
Facile synthesis and characterization of hyperbranched poly(aryl ether ketone)s obtained via an A2 + BB′2 approach
Authors: Li Xiujie , Zhang Shuling , Wang Hui , Pang Jinhui , Sun Dong , Mu Jianxin , Wang Guibin , Jiang Zhenhua
Published: June 2010

A fast and highly efficient approach for the synthesis of hyperbranched poly(aryl ether ketone)s (HPAEKs) via the polycondensation of A2 and BB′2 monomers is described. Commercially available hydroquinone (HQ, A2 monomer) and easily synthesized 2,4′,6‐trifluorobenzophenone (TF, BB′2 monomer) were thermally polycondensed to prepared fluoro‐ or phenolic‐terminated HPAEKs with K2CO3 and Na2CO3 as catalysts. During the reaction, the fluorine at the 4′‐position of TF reacts rapidly with the phenolic group of HQ, forming predominantly dimers and some other species. The dimer can be considered as a new AB′2 monomer. Further reactions among molecules AB′2 and AB′2 with some other species result in the formation of HPAEKs. Fourier transform infrared and 1H NMR spectra revealed the structures of the resultant polymers. The degree of branching (DB) of the fluoro‐terminated hyperbranched polymers was determined to be in the range 50–57% from 1H NMR spectra, whereas the DB of the phenolic‐terminated hyperbranched polymers was determined to be 100%. These hyperbranched polymers exhibit excellent solubility in general organic solvents and possess moderate molecular weights with broad distributions determined using gel permeation chromatography. Moreover, the structure and performance of the HPAEKs can be conveniently regulated by adjusting the type and feed ratio of the two monomers. Copyright © 2010 Society of Chemical Industry
Synergistic reinforcement of nanoclay and carbon black in natural rubber
Authors: Qu Liangliang , Huang Guangsu , Zhang Peng , Nie Yijing , Weng Gengsheng , Wu Jinrong
Published: June 2010

The synergistic reinforcement of nanoclay (NC) and carbon black (CB) in natural rubber (NR) has not been much studied. Therefore, the reinforcement mechanism was probed using synchrotron wide‐angle X‐ray diffraction and transmission electron microscopy (TEM) observation and analyzed in terms of tube model theory. A synergistic effect in reinforcement between NC and CB was proved by the marked enhancement in tensile strength from 11.4 MPa for neat NR to 28.2 MPa for NR nanocomposite with 5 wt% NC and 20 wt% CB. From a study of crystallization under deformation it was found that crystallization plays a less important role in the reinforcement of NR/NC/CB. Analysis using tube model theory provided more evidence for the synergistic effect. NR containing a combination of NC and CB exhibited an increase of topological tube‐like constraints in comparison with NR/CB. That is to say, in NR/NC/CB nanocomposites, a CB–NC local filler network, as indicated by TEM images, induced a more entangled structure in which mobility of rubber chains was hindered for lateral fluctuations by the presence of neighboring chains. The synergistic reinforcement of NC and CB in NR/NC/CB nanocomposites can be reasonably understood as due to the formation CB–NC local filler networks. Copyright © 2010 Society of Chemical Industry
Synthesis and characterization of polyesters based on 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane
Authors: More Arvind S , Naik Parimal V , Kumbhar Kishor P , Wadgaonkar Prakash P
Published: June 2010

Aromatic polyesters are of considerable interest because of their excellent mechanical properties, chemical resistance and thermal stability. However, most aromatic polyesters are difficult to process due to their high glass transition temperatures coupled with their insolubility in common organic solvents. The present article describes a series of organosoluble polyesters and copolyesters based on 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane. A series of new aromatic polyesters containing pendant pentadecyl chains was synthesized by interfacial polycondensation of 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane with terephthalic acid chloride (TPC), isophthalic acid chloride (IPC) and a mixture of TPC and IPC. A series of copolyesters was synthesized from 4,4′‐isopropylidenediphenol with TPC by incorporating 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane as a comonomer. Inherent viscosities of the polyesters and copolyesters were in the range 0.72–1.65 dL g−1 and number‐average molecular weights were in the range 18 170–87 220. The polyesters and copolyesters containing pendant pentadecyl chains dissolved readily in organic solvents such as chloroform, dichloromethane, pyridine and m‐cresol and could be cast into transparent, flexible and apparently tough films. Wide‐angle X‐ray diffraction data revealed the amorphous nature of the polyesters and copolyesters. The formation of loosely developed layered structure was observed due to the packing of pendant pentadecyl chains. The temperature at 10% weight loss, determined using thermogravimetric analysis in nitrogen atmosphere, of the polyesters and copolyesters containing pendant pentadecyl chains was in the range 400–460 °C. The polyesters and copolyesters exhibited glass transition temperatures in the range 63–82 °C and 177–183 °C, respectively. Copyright © 2010 Society of Chemical Industry
Niobium oxide solid catalyst: esterification of fatty acids and modeling for biodiesel production
Authors: de Araújo Gonçalves Jussara , Ramos André Luis Dantas , Rocha Layla L. L. , Domingos Anderson Kurunczi , Monteiro Robson S. , Peres José Sotolongo , Furtado Nelson C. , Taft Carlton A. , Aranda Donato A. G.
Published: June 2010

Biodiesel can be obtained from fatty acid raw materials through esterification. The reactivity of lauric, palmitic, stearic, oleic, and linoleic fatty acids with methanol using powdered niobic acid as a heterogeneous catalyst was investigated in this work, both experimentally (in a batch reactor) and theoretically. A 23 experimental design was used, with methanol/fatty acid molar ratio, catalyst concentration, and temperature as main factors. An empirical model demonstrated that temperature is the most important variable. Fourteen heterogeneous and 56 homogeneous‐like kinetic models were tested. A homogeneous‐like model considering zero order for all species and inhibition by water was the most adequate for experiments without catalyst. A homogeneous‐like model considering a second‐order reaction in relation to the fatty acid and no water inhibition was the most adequate for niobic acid catalyzed reaction. Molecular modeling confirmed the experimental results showing that the reactivity is directly related to the increase of unsaturated bonds and the reduction of carbon chain length. The polarity of the fatty acid is determinant in the reactivity. At the molecular level, reaction occurs between the HOMO orbital of methanol and LUMO orbitals of fatty acids and reactivity is higher when the energy difference between these orbitals is lower. Copyright © 2010 John Wiley & Sons, Ltd.
The internal thioester and the covalent binding properties of the complement proteins C3 and C4
Authors: Law S. K. Alex , Dodds Alister W.
Published: June 2010

The covalent binding of complement components C3 and C4 is critical for their activities. This reaction is made possible by the presence of an internal thioester in the native protein. Upon activation, which involves a conformational change initiated by the cleavage of a single peptide bond, the thioester becomes available to react with molecules with nucleophilic groups. This description is probably sufficient to account for the binding of the C4A isotype of human C4 to amino nucleophiles. The binding of the C4B isotype, and most likely C3, to hydroxyl nucleophiles, however, involves a histidine residue, which attacks the thioester to form an intramolecular acyl‐imidazole bond. The released thiolate anion then acts as a base to catalyze the binding of hydroxyl nucleophiles, including water, to the acyl function. This mechanism allows the complement proteins to bind to the hydroxyl groups of carbohydrates found on all biological surfaces, including the components of bacterial cell walls. In addition, the fast hydrolysis of the thioester provides a means to contain this very damaging reaction to the immediate proximity of the site of activation.
1,25‐dihydroxyvitamin D3 and PI3K/AKT inhibitors synergistically inhibit growth and induce senescence in prostate cancer cells
Authors: Axanova Linara S. , Chen Yong Q. , McCoy Thomas , Sui Guangchao , Cramer Scott D.
Published: June 2010

BACKGROUND

1‐Alpha, 25‐dihydroxyvitamin D3 (1,25(OH)2D3) inhibits proliferation of multiple cancer cell types including prostate cells and upregulates p21 and/or p27, while loss of Pten and PI3K/AKT activation stimulates survival and downregulates p21 and p27. We hypothesized that inhibition of the PI3K/AKT pathway synergizes with the antiproliferative signaling of 1,25(OH)2D3.

METHODS

Viability, cell cycle and senescence of cells were evaluated upon combinational treatment with 1,25(OH)2D3 and pharmacological PI3K/AKT inhibitors.

RESULTS

Pharmacological inhibitors of PI3K or Akt and 1,25(OH)2D3 synergistically inhibited growth of DU145, LNCaP, primary human prostate cancer cell strains and Pten null mouse prostatic epithelial cells (MPEC). The inhibitors used included API‐2 (Triciribine) and GSK690693 which are currently in clinical trials for treatment of cancer. A novel mechanism for antiproliferative effects of 1,25(OH)2D3 in prostate cells, induction of senescence, was discovered. Combination of 1,25(OH)2D3 and AKT inhibitor cooperated to induce G1 arrest, senescence, and p21 levels in prostate cancer cells. As AKT is commonly activated by PTEN loss, we evaluated the role of Pten in responsiveness to 1,25(OH)2D3 using shRNA knockdown and by in vitro knockout of Pten. MPEC that lost Pten expression remained sensitive to the antiproliferative action of 1,25(OH)2D3, and showed higher degree of synergism between AKT inhibitor and 1,25(OH)2D3 compared to Pten‐expressing counterparts.

CONCLUSIONS

These findings provide the rationale for the development of therapies utilizing 1,25(OH)2D3 or its analogs combined with inhibition of PI3K/AKT for the treatment of prostate cancer. Prostate 70: 1658–1671, 2010. © 2010 Wiley‐Liss, Inc.
Inhibition of angiopoietin‐2 in LuCaP 23.1 prostate cancer tumors decreases tumor growth and viability
Authors: Morrissey Colm , Dowell Alex , Koreckij Theodore D. , Nguyen Holly , Lakely Bryce , Fanslow William C. , True Lawrence D. , Corey Eva , Vessella Robert L.
Published: June 2010

BACKGROUND

Angiopoietin‐2 is expressed in prostate cancer (PCa) bone, liver, and lymph node metastases, whereas, its competitor angiopoietin‐1 has limited expression in these tissues. Therefore, we hypothesized that the inhibition of angiopoietin‐2 activity in PCa will impede angiogenesis, tumor growth, and alter bone response in vivo.

METHODS

To test our hypothesis we used L1‐10, a peptide‐Fc fusion that inhibits interactions between angiopoietin‐2 and its receptor tie2. We blocked angiopoietin‐2 activity using L1‐10 in established subcutaneous and intra‐tibial LuCaP 23.1 xenografts. We then determined the effect of L1‐10 on survival, tumor growth, serum PSA, proliferation, microvessel density, and angiogenesis‐associated gene expression in subcutaneous tumors. We also determined serum PSA, tumor area, and bone response in intra‐tibial tumors.

RESULTS

The administration of L1‐10 decreased tumor volume and serum PSA, and increased survival in SCID mice bearing subcutaneous LuCaP 23.1 tumors. Histomorphometric analysis, showed a further significant decrease in tumor epithelial area within the L1‐10 treated LuCaP 23.1 subcutaneous tumors (P = 0.0063). There was also a significant decrease in cell proliferation (P = 0.012), microvessel density (P = 0.012), and a significant increase in ANGPT‐2 and HIF‐1α mRNA expression (P ≤ 0.05) associated with L1‐10 treatment. Alternatively, in LuCaP 23.1 intra‐tibial tumors L1‐10 treatment did not significantly change serum PSA, tumor area or bone response.

CONCLUSIONS

Our results demonstrate that inhibiting angiopoietin‐2 activity impedes angiogenesis and growth of LuCaP 23.1 PCa xenografts. Based on these data, we hypothesize that angiopoietin‐2 inhibition in combination with other therapies may represent a potential therapy for patients with metastatic disease. Prostate 70: 1799–1808, 2010. © 2010 Wiley‐Liss, Inc.
Cross‐resistance and possible mechanisms of chlorpyrifos resistance in Laodelphax striatellus (Fallén)
Authors: Wang Lihua , Zhang Yueliang , Han Zhaojun , Liu Yanhe , Fang Jichao
Published: June 2010

BACKGROUND: Laodelphax striatellus (Fallén) is a major pest of cultivated rice and is commonly controlled in China with the organophosphate insecticides. To develop a better resistance management strategy, a chlorpyrifos‐resistant strain of L. striatellus was selected in the laboratory, and its cross‐resistance to other insecticides and possible mechanisms of the chlorpyrifos resistance were investigated.

RESULTS: After 25 generations of selection with chlorpyrifos, the selected strain of L. striatellus developed 188‐fold resistance to chlorpyrifos in comparison with the susceptible strain, and showed 14‐ and 1.6‐fold cross‐resistance to dichlorvos and thiamethoxam respectively. There was no apparent cross‐resistance to abamectin. Chlorpyrifos was synergised by the inhibitor triphenyl phosphate; the carboxylesterase synergistic ratio was 3.8 for the selected strain, but only 0.92 for the susceptible strain. The carboxylesterase activity of the selected strain was approximately 4 times that of the susceptible strain, whereas there was no significant change in the activities of alkaline phosphatase, acid phosphatase, glutathione S‐transferase and cytochrome P450 monooxygenase between the strains. The Michaelis constant of acetylcholinesterase, maximum velocity of acetylcholinesterase and median inhibitory concentration of chlorpyrifos‐oxon on acetylcholinesterase were 1.7, 2.5 and 5 times higher respectively in the selected strain.

CONCLUSION: The high cross‐resistance to the organophosphate dichlorvos in the chlorpyrifos‐resistant strain suggests that other non‐organophosphate insecticides would be necessary to counter resistance, should it arise in the field. Enhanced activities of carboxylesterase and the acetylcholinesterase insensitivity appear to be important mechanisms for chlorpyrifos resistance in L. striatellus. Copyright © 2010 Society of Chemical Industry
Syntheses and activities of backbone‐side chain cyclic octapeptide ligands with N‐functionalized phosphotyrosine for the N‐terminal SH2‐domain of the protein tyrosine phosphatase SHP‐1
Authors: Zoda Mohammad Safa , Zacharias Martin , Reissmann Siegmund
Published: June 2010

The protein tyrosine phosphatase SHP‐1 plays an important role in many physiological and pathophysiological processes. This phosphatase is activated through binding of ligands to its SH2‐domains, mainly to the N‐terminal one. Based on a theoretical docking model, backbone‐to‐side chain cyclized octapeptides were designed as ligands. Assembly of such modelled structures required the synthesis of N‐functionalized tyrosine derivatives and their incorporation into the sequence. Because of difficulties encountered in the condensation of N‐protected amino acids to the N‐alkylated tyrosine‐peptide we synthesized and used preformed dipeptide building units. As all attempts to obtain phosphorylated dipeptide units failed, the syntheses had to be performed with a free phenolic function. Use of different N‐alkyl or cycloalkyl residues in the N‐functionalized side chains allowed to investigate the effect of ring size, flexibility and hydrophobicity of formed lactam bridges on stimulatory activity. All tested linear and cyclic octapeptides stimulate the phosphatase activity of SHP‐1. Stimulatory activities of cyclic ligands increase with the chain length of the lactam bridges resulting in increased flexibility and better entropic preformation of the binding conformation. The strong activity of some cyclic octapeptides supports the modelled structure. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.
Electron‐beam‐induced fabrication of metal‐containing nanostructures
Authors: Kislov N. A. , Khodos I. I. , Ivanov E. D. , Barthel J.
Published: June 2010

An experimental system based on a transmission electron microscope JEM‐100CX has been developed for electron beam‐induced chemical vapor deposition. Direct electron beam‐induced growth of nanometer‐wide self‐supporting rods has been performed inside the microscope operating in scanning mode by decomposition of carbonyls of chromium Cr(CO)6, tungsten W(CO)6, and rhenium Re2(CO)10. In situ phase and structure transformations under annealing inside the microscope column were studied. Nanoscale rods and strips grown from rhenium carbonyl are of special interest because, after annealing, they consist of a single pure rhenium phase. The described method of metallic nanoelements fabrication enables us to produce highly conductive nanowires and tips for application in nanoelectronics, emission electronics, and scanning tunneling microscopy.
Advantages of backscatter electron imaging scanning electron microscopy for intracellular localization of cardiac analytes by gold conjugated antibody
Authors: Lea Peter. , Lee Lilian M. Y. , WeiShi Qin. , Takahashi Miyoko , Youn Woo , Jackowski George
Published: June 2010

Myoglobin and myosin light chain1 (MLC1) are intracellular human cardiac marker proteins which are released as a consequence of ischemia. Human cardiomyocytes were isolated from fresh biopsies and also maintained for several passages in cell culture. The cardiomyocytes were fixed in 100% methanol at −20°C, and labeled. The immunolocalization of intracellular antigen by fluorescence conjugated imaging was compared with scanning electron microscopy (SEM) backscatter electron (BSE) imaging of gold conjugated antibody. Ultraviolet light microscopy showed the intracellular distribution of both proteins to be mainly in the nuclear envelope, the cytoplasm immediately surrounding the nucleus and along portions of the cell membrane. To confirm this observed distribution of myoglobin and MLC1, labeling was repeated with antimyoglobin and anti‐MLC1 monoclonal antibodies conjugated to colloidal gold particles. The advantage of colloidal gold labeling is that the intracellular antigen‐antibody complexes may be more precisely located because of the significant improvement in resolution provided by BSE imaging in the SEM. BSE imaging confirmed the presence and subsarcolemma localization of myoglobin in cardiomyocytes directly isolated from fresh biopsies. The distribution of colloidal gold‐conjugated antibodies did not coincide with the intracellular distribution of the two proteins in the cardiomyocytes grown in cell culture as indicated by immunofluorescence. A relatively random, intracellular gold particle distribution was confirmed by x‐ray microanalysis. BSE imaging resulted in consistent auto‐backscatter labeling patterns very similar to the labeling patterns obtained with immunofluorescent labeling. X‐ray microanalysis confirmed that these auto‐backscatter labeling patterns were formed by concentrations of intracellular phosphate. Sodium dodecyl sulfate‐polyacrylamide gel eletrophoresis (SDS‐PAGE) and subsequent Western blotting indicated that myoglobin and MLC1 were no longer present in detectable quantities in these cells after several passages. Polymerase chain reaction (PCR) amplification of mRNA for human myoglobin and cardiac MLC1 confirmed the absence of their transcripts. Electrophoretic analysis of proteins in cardiomyocytes grown in cell culture confirmed an increasing presence of alkaline phosphatase. Staining of this enzyme with 5–bromo‐4–chloro‐3–indolyl phosphate and nitroblue tetrazolium showed that alkaline phosphatase was distributed in the same intracellular pattern as the fluorescence conjugated antibody and the phosphate auto‐backscatter. These results indicate that high‐resolution backscatter SEM imaging may be used as necessary control to confirm fluorescence light microscope intracellular labeling of antigens.
Magnetic refinement of tips for magnetic force microscopy
Authors: Bauer P. , Bochem H. P. , Leinenbach P. , Memmert U. , Schelten J.
Published: June 2010

Silicon cantilever probes with monolithically integrated tips are commercially available and are routinely used for atomic force microscopy (AFM). For such probes, amagnetic refinement of the silicon tip has been developed and results in a deposition of ferromagnetic material such as nickel or CrCoTa in the top area of the tip. The method consists of essentially three steps: (1) A broad‐area sputter deposition of a ferromagnetic material; (2) a selective electron beam‐induced carbon deposition at the top of the tip; (3) a broad‐area ion‐beam sputter etching, which removes the magnetic layer everywhere except underneath the carbon cap. The method allows to control the total amount and extension of the magnetic material left at the tip. It is applicable to all kinds of ferromagnetic materials which can be deposited as a thin layer by sputter deposition or evaporation. Experiments indicate that the method is reliable and improves the resolution of magnetic force microscopy (MFM). With such magnetically refined tips on silicon cantilevers, MFM measurements have been performed in contact mode as well as in dynamic and static noncontact modes. In this paper, the method for magnetic tip refinement is described and MFM measurements with these tips are presented.
Angioarchitecture of the terminal vascular system in inflammatory bowel disease—A comparative corrosion‐anatomic study
Authors: Busch C. , Gawad K. A. , Prenzel K. L. , Knoefel W. T. , Izbicki J. R. , Broelsch C. E.
Published: June 2010

The vascular origin of Crohn's disease (CD) and ulcerative colitis has been discussed but is poorly understood and investigated. A comparison of both diseases on the basis of the angioarchitecture had yet to be performed to investigate vascular morphology further and to evaluate its relevance for the etiology and differential diagnosis. The vascular system of 29 human colonic specimens of patients with CD (n=10), ulcerative colitis (n=11), and colon cancer (n=8), which were taken as controls, was perfused blood‐free immediately after resection. Corrosion casts were obtained by injection of Mercox Cl and consecutive digestion with potassium hydroxide. Casts were then cut into sections, sputter coated with gold, and examined in a blinded fashion by scanning electron microscopy. Normal intestine showed a typical honeycomb appearance, the mucosal capillary network was smooth and regular, and the subepithelial vascular plexus was supplied by regularly arranged arterioles. In CD, a partially intact capillary net with alterations, dominant collecting veins, and a characteristic pattern of diameter changes with narrow segments in the capillary bed was seen. In ulcerative colitis a disruption of the colonic vascular architecture was found. The capillarization was rarefied and irregular lumps of subepithelial capillary structures were observed. The morphology of the terminal vascular bed in inflammatory bowel disease in contrast to normal controls is uniquely described. The technique of injecting fresh, human specimens was applied for the first time. The homogeneity of vascular changes within each entity seems to allow a differentiation between CD and ulcerative colitis.
Key morphologic changes and DNA strand breaks in human lymphoid cells: Discriminating apoptosis from necrosis
Authors: Fairbairn Daryl W. , Walburger David K. , Fairbairn Joshua J. , O'Neill Kim L.
Published: June 2010

Apoptosis is an important form of physiologic cell death displayed by an enormous variety of tissues under divergent conditions. The recent attention toward apoptosis in virtually all aspects of modern biology indicates that rapid and accurate differentiation between apoptosis and necrotic death is of considerable interest. Apoptosis is distinguishable from necrosis on the basis of several criteria. In this study, we undertook to examine the effects of mild hyperthermia (43°C leading to apoptotic death) and severe hyperthermia (50°C leading to necrotic killing) on associated DNA fragmentation. Using laser scanning and fluorescent microscopic evaluation of DNA “comets” in the single cell gel assay, we compared necrotic and apoptotic DNA damage in a variety of human leukemia and lymphoma cell lines at the level of the individual cell. We show that necrotic cells do display detectable DNA damage. We confirm our preliminary report that comet “tail moment” is sufficient to distinguish between necrotic and apoptotic DNA damage, while comet tail length may confuse the two forms. We report that a recovery period is necessary for expression of increasing apoptotic but not necrotic DNA damage. We show that apoptosis increases with prolonged hyperthermia and confirm that the mode of death changes from apoptosis to necrosis with higher heat loads, producing a greater fraction of cells showing damage. In addition, we show that for necrotic cells, DNA tail moment reflects sensitivity to prolonged exposure without a concomitant change in tail length.
Digital photogrammetric quantification of surface area and volume on scanning electron micrographs of frozen hydrated lung tissue
Authors: Poinar H. N. , Strohman R. D. , Lee C. Y. , Bastacky S. J.
Published: June 2010

A digital video plotter (DVP, Leica), the personal computer equivalent of an analytical plotter, was used to measure the coordinates of points chosen from stereo pair images of the surface of frozen hydrated lung imaged at magnifications of 2000 and 5000x with a low‐temperature scanning electron microscope (SEM). Rat lung tissue was frozen in vivo with a liquid nitrogen cryoprobe under carefully controlled physiologic conditions. At slow freezing rates, water in the aqueous layer at the surface of the lung segregates into ice crystals (dendrites) which branch in the plane of the surface. Coordinates of points on dendrite surfaces were measured by the DVP and passed to TERRAMODEL (Plus III Software, a land modeling program) where they were used to generate a three‐dimensional model, from which surface area and planimetric area of the lung surface were calculated. Additional measurements were made at the top and bottom of the ice structures and a Basic language program was written to calculate the volume of ice on the lung surface. Digital photogrammetry coupled with low‐temperature SEM of frozen samples allows measurement of water and water‐containing microstructures ubiquitous in biology.
The role of the environmental scanning electron microscope in the investigation of cement‐based materials
Authors: Neubauer C. M. , Jennings H. M.
Published: June 2010

The role of the environmental scanning electron microscope (ESEM) in the study of cement‐based materials is reviewed. Since water is an intrinsic part of the microstructure of cement paste, techniques that facilitate the study of wet specimens are necessary. The evolution of techniques is traced from standard microscopic methods to the use of the ESEM for in situ analysis. The importance of past and current work is discussed, including novel analytical methods designed for the study of cement pastes. Directions for future work are also discussed.
Applications of the environmental scanning electron microscope to the analysis of pharmaceutical formulations
Authors: Emanuele Antony D. , Gilpin Christopher
Published: June 2010

Electron microscopy has been used for several years as a routine tool for the study of pharmaceutical formulations. However, it is usually desirable to obtain information on these systems in the wet state, and there are concerns regarding the interpretation of information provided by conventional electron microscopy where samples are subjected to preparation techniques which may include freezing, drying, fracturing, and coating. The environmental scanning electron microscope (ESEM) has been used to analyse a number of pharmaceutical samples in their natural state. Results obtained from these samples, including biodegradable matrices, microparticulate systems (both degradable and non‐biodegradable), and bioadhesive matrices, will be discussed and the merits and limitations of the ESEM will be highlighted.
Image sharpness measurement in scanning electron microscopy—part I
Authors: Chae Postek M. L. T. , Vladár András E.
Published: June 2010

This study introduces the idea of the sharpness concept in relationship to the determination of scanning electron microscope (SEM) performance. Scanning electron microscopes are routinely used in many manufacturing environments. Fully automated or semiautomated SEMs as metrology instruments are used in semiconductor production and other forms of manufacturing where the ability to measure small features with the smallest possible errors is essential. It is felt that these automated instruments must be routinely capable of 5 nm (or better) resolution at or below 1 kV accelerating voltage for the measurement of nominal 0.18–0.35 μm size parts of the integrated circuits. Testing and proving on a day‐by‐day basis that an instrument is performing well is not easy, but, understandably, is an industry need and concern. Furthermore, with the introduction of fully automated inspection and metrology instrumentation, not only does an appropriate, easy to obtain or manufacture sharpness measurement sample have to exist but also an objective and automated algorithm must be developed for its analysis. Both of these have been the object of a study at the National Institute of Standards and Technology (NIST), and the fundamentals are discussed in this paper and the computer‐based automated analysis in a companion paper (Part II; Vladáret al. 1998). The method described in these papers is based on the analysis of the frequency domain representation of the SEM image and can also be used to check and optimize two basic parameters—focus and astigmatism—of the primary electron beam as related to a measure of image sharpness. The application of this technique to check regularly the resolution of the SEM in quantitative form will also be discussed.
Mean atomic number and backscattered electron coefficient calculations for some materials with low mean atomic number
Authors: Howell P. G. T. , Davy K. M. W. , Boyde A.
Published: June 2010

In modelling electron backscattering from solids using Monte Carlo simulations, knowledge of mean atomic number, mean atomic weight, and density of the bulk material are required. We studied four different ways in common useforthe calculation of mean atomic number. An alternative and improved approach is to calculate the mean backscattered electron (BSE) coefficient, η, from a knowledge of the elemental composition and values of η for the elements. Again, we studied a number of formulae suggested for this averaging process. As it is not possible to measure η directly for a number of elements, the method used to interpolate between elements with known η was also examined. In addition, we obtained experimental backscattering relationships for topography‐free samples of poly (methylmethacrylate) (PMMA), carbon, aluminium, and a series of novel halogenated resins, all solids with relatively low mean atomic numbers, and calcified tissues. None of the methods for determining mean atomic number placed the materials of interest in the correct sequence of their experimentally determined BSE peaks: the data differed widely between the individual methods. The averaged BSE coefficient calculated by the Castaing formula gave the best agreement with the experimentally derived data.
Three‐dimensional reconstruction and modeling of microstructures and microchemistry in geological materials
Authors: Marschallinger Robert
Published: June 2010

Computer‐aided three‐dimensional (3‐D) reconstruction of minerals and rock fabrics enables quantification, spatial analysis, and state of the art communication of the complex spatial relations typically encountered in geological materials. An efficient and versatile combination of sample preparation, data acquisition, and processing methods has been established which renders the 3‐D reconstruction of microstructures in geological materials applicable on a routine basis: rock samples are subject to a cycle of precision serial lapping and subsequent image acquisition by an electron probe microanalyzer. The yielded backscattered electron images and x‐ray maps depict mineral phase distribution and chemical variation; backscattered electron images are stacked in a voxel array to be interpolated by binary processing. X‐ray map data are interpolated by geostatistical methods, and the results are forwarded to one voxel array per chemical element of interest. Merging the voxel arrays by boolean and image algebraic methods enables the integrated analysis and visualization of mineral morphology and associated chemical variation in geological materials.
Toward a standard for remote microscope control systems
Authors: Morgan Christopher , Pardoe Don , Smith Nancy
Published: June 2010

Remote access to scientific instruments provides a way to share a variety of valuable resources with a worldwide audience. By pooling these resources and providing a common network and user interfaces to these resources, science researchers and educators will have capabilities that no one institution could afford. The Microscope And Graphic Imaging Center (MAGIC) at California State University, Hayward (CSU Hayward) is developing a model for such a system. We are developing model software for interactive remote‐shared access to an unmodified Philips XL 40 scanning electron microscope (SEM). Located within the Department of Biological Sciences, MAGIC provides facilities and expertise in specimen preparation as well as providing remote access to researchers and educators over the Internet. We have used a wide range of networking technologies, including modem, ISDN, Ethernet, T1, and ATM to control the SEM, and a wide range of image transmission technologies, including closed circuit TV, compressed video over ATM, and digital imaging (Smith et al. 1996a,b,c). We have taken a modular approach to software control which allows us to arrange key pieces in a variety of ways on a number of different platforms. Results indicate that under the correct conditions, access to expensive and sensitive commercially available scientific equipment can be shared by large research, educational, and industrial communities. However, care must be taken to address issues of security, robustness, and performance. Plans are to incorporate remote access into university, community college, and high school use starting in 1998. Based upon this experience, we propose a framework for standardizing remote access to visual scientific equipment. This framework consists of three layers: (1) clients, (2) servers, and (3) instruments. This approach will allow a wide variety of equipment to be shared in a flexible and uniform manner.
A low‐temperature scanning tunneling microscopy investigation of single electron effects
Authors: Drechsler T. , Chi L. F. , Fuchs H.
Published: June 2010

The design and the performance of a low‐temperature scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV) is described. The sample and the STM are cooled by means of a helium bath cryostate. The STM consists of a “beetle”‐type microscope, which is mounted on a spring suspension stage that can be operated between room temperature and 30 K. We present the results of tunneling spectroscopy on ligand‐stabilized Au55‐clusters on a thiol‐covered gold substrate. I(V)‐curves taken at 100 K clearly show coulomb staircase structures, which agree well with theoretical predictions for these structures.
Microstructure of the processing of black beans (Phaseolus vulgaris L.) from purée to drum‐dried flakes
Authors: Wood Delilah. F. , De J. Berrios Joseé , Venet Cecile
Published: June 2010

Black bean purée and drum‐dried flake microstructures were studied and compared with raw bean by light and scanning electron microscopies. Results illustrate the value of microscopy as a tool for evaluating physical and chemical changes in bean components due to processing. Microscopy was employed to follow the microstructural changes during the processing of black beans by looking at the intermediate product (the purée) and the end product (the flake). The consequences of processing on storage components such as starch, proteins, lipids, and cell walls were elucidated. The bean purée contained starch granules within intact cells and seed coat fragments throughout the product. The drum‐dried flakes had a rough exterior, and starch granules were also found within intact cells. Both starch granules and seed coat fragments were found in the drum‐dried flake matrices. Protein bodies, occurring in the raw bean, were present (but less obvious than in the raw bean) in both the bean purée and the drum‐dried flake. Cell contents that no longer occurred in intact cells consisted of fused protein bodies in both products. The seed coat did not change significantly during processing, and pieces of seed coat were easily differentiated throughout the bean purée and the drum‐dried flakes. The endosperm, which is closely adherent to the inner portion of the seed coat in the intact bean, was no longer evident in the processed samples, presumably because the endosperm tissue had completely solubilized following the addition of water. Lipids occurred as small droplets and were located throughout both the bean purée and the drum‐dried flakes. The bean purée consisted mostly of clumps of intact cotyledon cells with very few broken cells. The cotyledon cells contained intact starch granules with no evidence of starch gelatinization [i.e., the irreversible breakdown of the granule structure (Dengate 1984)]. Free starch granules in the purée, resulting from broken cells, were slightly swollen and had begun to gelatinize. Protein bodies were still evident in the purée, but no longer stained as in the raw, mature bean. The drum‐dried flakes contained intact and broken cotyledon cells. Intact cells contained protein bodies that were difficult to detect and appeared to be a rather continuous protein matrix. The cotyledon cells also contained partially gelatinized starch granules that remained mostly distinct but were beginning to fuse. Starch granules interspersed between intact cells were fused and completely gelatinized. The drum‐dried flake matrix consisted of a continuous mixture of protein, starch, and cell wall material.
Computer‐aided design helps design what may be world's smallest scanning tunneling microscope
Authors: Fasanella Kenn
Published: June 2010

Computer‐aided design (CAD) played a crucial role in designing what is believed to be the world's smallest scanning tunneling microscope. Conventional scanning tunneling microscopes (STMs) are 2) to 6) in diameter. NEC researchers needed an STM only 1) in diameter to study objects in a high magnetic field at very low temperature within a tank of liquid helium. NEC engineers built the microscope in‐house and at a local machine shop using a combination of commercial components and others that they built themselves. Computer‐aided design was crucial in the fitting of all the required components within the very tight envelope requirement. An inexpensive Macintosh and PC‐based CAD program, Vellumfrom Ashlar, Inc., San Jose, California, was used to evaluate a wide range of possible configurations in minimal time.
Sintering of Sio2‐Tio2 obtained by the sol‐gel process from chelated Ti precursors
Authors: Méndez‐vivar J. , Mendoza‐Serna R.
Published: June 2010

Two experimental procedures were used to obtain SiO2‐TiO2. In one case, the Si precursor was prehydrolyzed before reacting with Ti to equalize the chemical reactivity of both reagents. In the other case, H2O was produced in situ to avoid precipitation of TiO2. Two chelating agents were also used separately to control the polymerization process. It was found that the type of chelating agent leads to differences in the particle size.
Mechanical properties of L929 cells measured by atomic force microscopy: Effects of anticytoskeletal drugs and membrane crosslinking
Authors: Wu H. W. , Kuhn T. , Moy V. T.
Published: June 2010

To shed light on the architecture of the cytoskeleton, we used the atomic force microscope (AFM) to measure the elasticity, viscoelasticity, and plasticity of L929 cells. The initial elastic response (Young's modulus ∼ 4,000 Pa) of the cells to an applied force was followed by a slow compression of the cytoskeleton (τ1/2 ≈ 10 s). When force application was terminated, the cytoskeleton underwent a sudden partial decompression and a subsequent slow, incomplete recovery. The role of the cytoskeletal elements in cell mechanics was accessed in AFM measurements carried out on cells treated with cytochalasin D, nocodazole, or col‐cemid. Cytochalasin D treatment reduced both elasticity (∼45%) and cytoplasmic viscosity (∼65%), whereas cells treated with nocodazole or colcemid exhibited a marked increase in elasticity (∼100%) and a slight increase in viscosity (∼15%). The AFM force measurements also provided evidence that the cell membrane and the cytoskeleton are mechanically coupled. Tightly adherent cells were stiffer than cells that were loosely attached. Moreover, cells crosslinked with either glutaraldehyde, 3,3 ‘‐dithiobis’sul‐fosuccinimidylpropionate] (DTSSP), or Concanavalin A were more rigid than untreated cells. It is of interest that cells crosslinked with Concanavalin A, but not DTSSP, displayed plastic behaviors that may reflect the induction of cytoskeletal reorganization by Concanavalin A.
Quantitative secondary ion mass spectrometry imaging of self‐assembled monolayer films for electron beam dose mapping in the environmental scanning electron microscope
Authors: Gillen Greg , Wight Scott , Bright David , Herne Tonya
Published: June 2010

Fluorinated alkanethiol self‐assembled monolayers (SAM) films immobilized on gold substrates have been used as electron‐sensitive resists to map quantitatively the spatial distribution of the primary electronbeam scattering in an environmental scanning electron microscope (ESEM). In this procedure, a series of electron dose standards are prepared by exposing a SAM film to electron bombardment in well‐defined regions at different levels of electron dose. Microbeam secondary ion mass spectrometry (SIMS) using Cs+ bombardment is then used to image the F‐ secondary ion signal from these areas. From the reduction in F‐ intensity as a function of increasing electron dose, a calibration curve is generated that allows conversion of secondary ion signal to electron dose on a pixel‐by‐pixel basis. Using this calibration, electron dose images can be prepared that quantitatively map the electron scattering distribution in the ESEM with micrometer spatial resolution. The SIMS imaging technique may also be used to explore other aspects of electron‐surface interactions in the ESEM.
Study of luminescent centers annealing in wide bandgap semiconductors: Color cathodoluminescence‐scanning electron microscopy
Authors: Mokhov E. N. , Roenkov A. D. , Saparin G. V. , Obyden S. K.
Published: June 2010

A color cathodoluminescence‐scanning electron microscopy (CCL‐SEM) technique was used to study the annealing of luminescent centers in wide bandgap semiconductors (mainly silicon carbide), due to native defects, induced during the growth process or to radiation by high‐energy particles. The significant role of dislocations in the crystals was revealed. These dislocations are created by the mechanical failure of crystals and play the role of getters for unstable defects and assist in quenching the luminescence at fairly low annealing temperatures. During the electron beam annealing of the samples, the resolved CL fine structure of luminescence images was measured around failure regions which look like a rosette of strength* at temperatures of 1300–1350°C.
Transmission line probes for scanning photon‐tunneling microscopy
Authors: McCutchen C. W.
Published: June 2010

Because metalized light probes for scanning photon‐tunneling microscopy are tapered waveguides beyond cutoff, tapered coaxial transmission lines have been tried instead. It is shown here that insertion losses in such a line can be reduced by asymmetrically phase‐apodizing the illuminating lens. Alternatively, a strip rather than a coaxial line can be used.
High‐resolution photon scanning tunneling microscopic investigations of NaCl crystal surfaces
Authors: Brückl H. , Pagnia H. , Sotnik N.
Published: June 2010

Cleaved NaCl crystal surfaces were investigated with a photon scanning tunneling microscope. Steps 4 nm high and 3 nm wide could be resolved. The lateral resolution is coupled to the step height by the steepest measured slopes of about 50°. The measured stepwidth at shallow steps is noise‐and slope‐limited to 3 nm. The mapping of the decay coefficient of the evanescent field shows spatial inhomogeneities often coupled to the crystalline structure.
The influence of elastic and ionization cross‐section approximations on the result of Monte Carlo calculations
Authors: Bakaleinikov L. A. , Tretyakov V. V.
Published: June 2010

A Monte Carlo program has been developed on the basis of a Mott cross‐section and knock‐on model. The use of this program for the set of the film‐substrate type systems shows that there is some difference between the calculated and experimental x‐ray depth distribution. To clear up the reasons for the discrepancies, the Monte Carlo model is investigated by calculating the various physical quantities associated with the electron distribution in homogeneous bulk and film specimens and by comparing them with the known experimental data. The influence of the elastic and ionization cross‐section approximation on the electron distribution in target is studied.