bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numeric simulation of permafrost degradation in the eastern Tibetan Plateau
Authors: Li Dongqing , Chen Jin , Meng Qingzhou , Liu Dengke , Fang Jianhong , Liu Jiankun 
Published: February 2008

AbstractRates of permafrost degradation at both the permafrost table and the base of permafrost were simulated using a prescribed rate of increase in mean annual air temperatures of 0.04°C/a for a site in continuous permafrost near Changshitou Mountain, eastern Tibetan Plateau. The results indicate that over 110 years, the permafrost table descends from a depth of 1.20 m to 1.48 m, and that the base of permafrost rises from the initial value of 55.0 m to 15.2 m. The predicted rate of basal permafrost degradation in low moisture content bedrock reaches a peak of 0.58 m/a after 60 years, assuming a constant thermal gradient at the base of 0.018°C/m. The permafrost is persistent due to the ice‐rich nature of the near‐surface soil layers. Copyright © 2008 John Wiley & Sons, Ltd.
Partially circumventing peripheral tolerance for oncogene‐specific prostate cancer immunotherapy
Authors: Neeley Yilin C. , Arredouani Mohamed S. , Hollenbeck Brent , Eng Marvin H. , Rubin Mark A. , Sanda Martin G. 
Published: February 2008

AbstractBACKGROUNDFailure of cancer immunotherapy is essentially due to immunological tolerance to tumor‐associated antigens (TAAs), as these antigens are also expressed in healthy tissues.METHODSHere, we used transgenic adenocarcinoma of mouse prostate (TRAMP) mice, which develop lethal prostate cancer due to prostate‐specific expression of SV40 T antigen (Tag), to evaluate effects of prostatic transformation on oncogene TAA‐specific tolerance and to test the possibility of breaking such tolerance using a modified recombinant vaccinia virus.RESULTSWe showed that Tag expression in TRAMP mice is uniquely extra‐thymic, and levels of prostatic Tag expression positively correlate with malignant transformation of the prostate. Yet, young tumor‐free TRAMP mice were tolerant to Tag antigen. We therefore attempted overcoming such peripheral oncogene‐specific T cell tolerance through immunization with a vaccinia construct encoding Tag immunogenic epitopes. This vaccination modality showed that oncogene‐specific tolerance was successfully overcome by effective in vivo priming of Tag‐specific cytotoxic T cells (CTLs). However, this was restricted to young TRAMP mice. Tag‐specific CTL from “tumor naïve” young TRAMP mice showed significant anti‐tumor efficacy in vivo by eliminating established heterotopic prostate tumors and prolonging survival in SCID mice harboring Tag‐expressing tumors. In contrast, older TRAMP mice with established prostate tumors exhibited oncogene‐specific tolerance as evidenced by failure to generate Tag‐specific CTL following Tag‐specific immunization.CONCLUSIONSPeripheral tolerance can be overcome for effective anti‐tumor therapy following oncogene‐specific immunization. However, this ability to elicit oncogene‐specific CTL is impeded in the tumor‐bearing host, in the context of increased oncogene expression associated with tumor progression. Prostate 68: 715–727, 2008. © 2008 Wiley‐Liss, Inc.
Evaluation of a variant in the transcription factor 7‐like 2 (TCF7L2) gene and prostate cancer risk in a population‐based study
Authors: Agalliu Ilir , Suuriniemi Miia , Prokunina‐Olsson Ludmila , Johanneson Bo , Collins Francis S. , Stanford Janet L. , Ostrander Elaine A. 
Published: February 2008

AbstractBackgroundTranscription factor 7‐like 2 (TCF7L2) is a high mobility group‐box containing protein that is a critical member of the Wnt/β‐catenin canonical signaling pathway. In addition to its recently recognized role in diabetes, aberrant TCF7L2 expression has been implicated in cancer through regulation of cell proliferation and apoptosis by c‐MYC and cyclin D. It has been hypothesized that germline variants within the TCF7L2 gene previously associated with diabetes may affect cancer risk through the Wnt/β‐catenin signaling pathway. Specifically, the same risk allele of single nucleotide polymorphism (SNP) rs12255372 that is associated with diabetes (T allele) has recently been associated with an increased risk of breast cancer.MethodsHere, we investigated associations between rs12255372 and prostate cancer risk among 1,457 cases and 1,351 controls from a population‐based study.ResultsThe variant TT genotype was not associated with overall prostate cancer risk. However, there was evidence that men homozygous for the variant T allele had an elevated relative risk of more aggressive prostate cancer, as defined by high Gleason score (OR = 1.7, 95% CI = 1.0–2.8) or regional/distant stage (OR = 1.7, 95% CI = 1.1–2.6) disease.ConclusionsOur findings suggest that this variant in the TCF7L2 gene may be associated with risk of developing more clinically significant disease. These results need to be confirmed, but provide initial evidence that the TCF7L2 gene may alter risk of developing more aggressive prostate cancer. Prostate 68: 740–747, 2008. © 2008 Wiley‐Liss, Inc.
Synthesis, characterization, and magnetic properties of flower‐like nickel materials
Authors: Zhou W. , Guo L. , He L. , Chen C. P. 
Published: February 2008

AbstractFlower‐like Ni particles about 1 µm in diameter have been synthesized by means of a mild chemical solution method with a soft template of hexadecyltrimethy‐lammonium bromide (CTAB). Analysis of the structures by scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM) reveal that they are composed of particles with an average diameter of 250 nm. The particles are composed of grains 20–30 nm in size. Based on a series of experiments, the growing process of the flower‐like structure is described briefly. The coercivity of the as‐grown product at 300 K is about 90 Oe. It is small in comparison with that of the reported flower‐like microstructure composed of nickel nanotips, ∼232 Oe. This is attributed to its shape anisotropy and polycrystalline structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ambipolar charge carrier transport in organic semiconductor blends of phthalocyanine and fullerene
Authors: Bronner Markus , Opitz Andreas , Brütting Wolfgang 
Published: February 2008

AbstractAmbipolar charge carrier transport is realised in organic field‐effect transistors using mixtures of p‐conductive copper‐phthalocyanine and n‐conductive buckminster fullerene as active layer. These blends are model systems for ambipolar transport with adjustable field‐effect mobilities for electrons and holes by variation of the mixing ratio. Thereby balanced mobilities for both charge‐carrier types are possible.In this paper we discuss the variation of mobility, threshold voltage and electronic energy levels with the mixing ratio. The charge carrier mobilities are strongly reduced upon dilution of the respective conducting phase by the other species. This shows that transport of each carrier species occurs by percolation through the respective phase in the blend. A strong correlation between contact resistance and mobility indicates that carrier injection is diffusion limited. A charge redistribution in the copper‐phthalocyanine causes a hole accumulation at the organic/organic interface and affects thereby the threshold voltage for holes. By analysing the electronic structure using photoelectron spectroscopy no charge transfer was found in the ground state. The common work function of these blends changes linearly between the work functions of the neat materials. Thus a constant ionisation potential for the highest occupied molecular orbitals of the two materials is obtained.Furthermore we have fabricated ambipolar inverters using mixed organic semiconductor layers and compare their behaviour to complementary inverters consisting of discrete p‐ and n‐channel transistors. The experimental findings and concomitant simulations demonstrate the need for balanced elec‐ tron and hole mobilities in order to achieve symmetric inverter characteristics. However, they also reveal the superior performance of true complementary logic inverters towards their ambipolar pendants. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of top layer geometries on the electronic properties of pentacene and diindenoperylene thin films
Authors: Scharnberg M. , Adelung R. , Faupel F. 
Published: February 2008

AbstractTop layers have a pronounced influence on the electronic properties of molecular organic thin films. Here, we report about the changes induced by metallic and polymeric top layers and contacts. As test structures, model systems of diindenoperylene and pentacene crystalline molecular organic thin films are used. A very sensitive radiotracer technique is introduced to study the details of metal penetration during top contact formation. The influence of temperature, evaporation time, adhesion promoter and grain size of the organic film were examined. The electric currents passing through metal top contacts were found to vary by more than a factor of three, depending on the preparation conditions of the metal contact. Furthermore, the series resistance of chemically identical contacts that only differed in the morphology of the interface were found to show pronounced asymmetric conductivity behaviour. We also show that with the help of electret top layers, based on the Teflon‐AF fluropolymer, the threshold voltage of an organic field effect transistor can be tuned by several volts. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Potentiometry on pentacene OFETs: Charge carrier mobilities and injection barriers in bottom and top contact configurations
Authors: Scholz R. , Lehmann D. , Müller A.‐D. , Müller F. , Zahn D. R. T. 
Published: February 2008

AbstractIn a combination of experimental techniques including electrical probes, potentiometry, and charge transient spectroscopy (QTS), we develop concepts how to quantify the potential drops at the contacts, the mobility in the channel region, and the density of states of deep traps in pentacene OFETs. For OFETs grown from unpurified pentacene on pre‐patterned Au bottom contacts, a comparison between potentiometry and two‐dimensional device simulations determines an injection barrier of 0.73 eV at the source contact and a hole mobility of 0.014 cm2 V–1 s–1 in the pentacene channel. Temperature‐dependent QTS data reveal a trap level at about 125 meV from the hole transport band, indicating a relatively high density of unintentional dopants and therefore a high background density of majority charge carriers. In OFETs grown from purified pentacene onto a SiO2 gate dielectric and Au top contacts evaporated onto the pentacene channel without breaking the vacuum, potentiometry reveals a nearly perfect alignment of the metal work function with the hole transport level in the organic layer. The much lower density of deep traps in these samples raises the hole mobility to the range 0.1–0.2 cm2 V–1 s–1. A further improvement of the hole mobility and the resulting device performance can be achieved by a chemical treatment of the gate oxide with n‐octadecytrichlorosilane (OTS). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic states at the dielectric/semiconductor interface in organic field effect transistors
Authors: Benson Niels , Melzer Christian , Schmechel Roland , Seggern Heinz von 
Published: February 2008

AbstractElectronic trap states at the interface of the gate insulator and the organic semiconductor play a decisive role for the current–voltage characteristic of organic field effect transistors. In this article two techniques will be introduced which eliminate and generate those trap states on SiO2 as well as polymer dielectric interfaces, respectively. Employing these interface modifications, p‐ and n‐type pentacene field‐effect transistors as well as an organic CMOS inverter with a single organic semiconductor and a single type of source–drain metallization were engineered. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray structural and crystallinity studies of low and high molecular weight poly(3‐hexylthiophene)
Authors: Joshi S. , Grigorian S. , Pietsch U. 
Published: February 2008

AbstractX‐ray diffraction studies were performed in order to understand the crystallinity, the molecular orientation and the nanoscale morphology of a low‐(LMW) and a high molecular weight (HMW) fractions of Poly(3‐hexylthiophene) (P3HT) thin films. The thickness of films was found to be in the range between 10 nm and 200 nm. Further structural information was obtained using X‐ray grazing incidence in‐plane and out‐of‐plane diffraction using synchrotron radiation. The X‐ray analysis reveals that the films are mainly amorphous and contain randomly oriented nanocrystallites with the best match for a monoclinic unit cell. Additionally, polymorphism was found for ∼200 nm thick films of LMW fraction. Interestingly, the film morphology varies as a function of the film thickness. For LMW material the random orientation of nanocrystallites changes to preferential orientation of lamellae along the surface normal when the size of crystallites become of the order of film thickness, i.e. below 20 nm. For the HMW fraction we found an increase of lamellar ordering at about 60 K below the melting point of the material. Temperature‐resolved measurements reveal a thickness dependence of crystallinity. For the LMW fraction the character of the phase transition changes from continuous drop of intensity (for thick films) to sharp drop of intensity for extremely thin films, which is a hint for the importance of the film to substrate interaction. The figure shows the proposed monoclinic unit cell of the P3HT low molecular weight fraction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Organic field‐effect transistors for spin‐polarized transport
Authors: Michelfeit M. , Schmidt G. , Geurts J. , Molenkamp L. W. 
Published: February 2008

AbstractIn order to combine the merits of the rapidly developing fields of spintronics and organic electronics, we present a concept of an organic field‐effect transistor (OFET) for spin‐polarized transport, enabling a non‐volatile activation and deactivation by magnetic field pulses. This new steering parameter in addition to the usual steering by the electrical gate voltage opens the path toward programmable logics. In our concept, the magnetic‐field sensitivity is achieved by the employment of ferromagnetic source and drain contacts with different coercive field strength. This enables a separate switching of its magnetization directions. The resulting parallel or anti‐parallel orientation of the magnetization of source and drain corresponds to a low or high channel resistance for the spin‐polarized electrons. On the route towards the experimental realization of this device, we present a working OFET, based on dihexylquaterthiophene (DH4T), with ferromagnetic FeCoB stripes as source and drain contacts. Besides, the ability of a separate switching of the contact stripe magnetizations is demonstrated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aluminum oxide film as gate dielectric for organic FETs: Anodization and characterization
Authors: Dang X.‐D. , Plieth W. , Richter S. , Plötner M. , Fischer W.‐J. 
Published: February 2008

AbstractThe influences of the preparation conditions on the properties of anodic aluminium oxide films were studied by electrochemical impedance spectroscopy. A two‐layer model of the film, consisting of barrier and porous layers was used to analyze the impedance data. The thickness of the barrier layer was calculated from the capacitance values. The total thickness of the aluminium oxide film was determined by cross‐section SEM micrographs. Thus, anodic aluminium oxide films were prepared showing dielectric properties comparable to that of silicon dioxide films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A study of magnetic properties in CoFeSiB amorphous thin films submitted to furnace annealing
Authors: Celegato F. , Coïsson M. , Olivetti E. , Tiberto P. , Vinai F. 
Published: February 2008

AbstractCo67Fe4Si14.5B14.5 amorphous thin films have been produced by rf sputtering with thickness varying from 30 nm to 90 nm. Differential scanning calorimetry and X‐ray diffraction have been employed to reveal a predominant amorphous phase in the as‐prepared samples, although a small crystalline fraction cannot be excluded. Selected specimens have been submitted to furnace annealing in vacuum with and without the application of an in‐plane magnetic field with an intensity of 100 Oe. At temperatures ≥550 °C the thin films develop a significant crystalline fraction responsible of the large increase of the coercivity of their magnetic hysteresis loops. Thicker films develop larger coercivities upon crystallization. Field annealing below the Curie temperature of the alloy results in the induction of a uniaxial magnetic anisotropy (rectangular hysteresis loop along the easy axis, almost linear loops along the hard axis). Sample thickness and annealing time affect the development of the uniaxial anisotropy and the remanence to saturation ratio. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Organic transistors utilising highly soluble swivel‐cruciform oligothiophenes
Authors: Zen Achmad , Pingel Patrick , Neher Dieter , Scherf Ullrich 
Published: February 2008

AbstractA series of soluble swivel‐cruciform oligothiophene dimers with increasing chain length – bis(terthiophene) (BT3), bis(pentathiophene) (BT5) and bis(heptathiophene) (BT7) – was used as semiconductor in organic field‐effect transistors. A field‐effect mobility of 3.7 × 10–5 cm2/Vs and a current on/off ratio of >103 was obtained with dimer BT5. The attachment of terminal n‐hexyls to BT5 provides a swivel‐cruciform α,α′‐dihexylpentathiophene dimer (DHPT‐SC) with increased solubility. XRD and AFM analysis of the resulting thin films reveals that they are highly crystalline. Using the DHPT‐SC swivel cruciform in solution‐processed organic field‐effect transistors, we obtained a field‐effect mobility of 0.012 cm2/Vs and a current on/off ratio of >105, which is among the highest values reported to date for wet‐processed OFETs utilizing oligothiophenes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of Alq3 and/or Al2O3 layers at the C60/aluminum interface on the I –V characteristics of CuPc/C60‐based solar cells
Authors: Morsli M. , Berredjem Y. , Drici A. , Kouskoussa B. , Boulmokh A. , Bernède J. C. 
Published: February 2008

AbstractThe electrical properties of organic solar cells based on the couple copper phthalocyanine/fullerene (CuPc/C60) have been studied as a function of the interface fullerene/aluminum (C60/Al). It is shown that, in the case of direct contact, the cells properties depend on the ageing of the cells. Indeed, when the cell is in contact for 5 min with air before encapsulation, i.e. when a thin natural alumina (Al2O3) layer is present between the C60 and Al there is an increase of the open‐circuit voltage, which is attributed to an increase of the shunt resistance. When a tris(8‐hydroxyquinoline) (Alq3) thin film is introduced between the C60 and the Al, ageing of the devices, that is to say the contact or not for 5 min with air before encapsulation, does not strongly modify the cells properties. The presence of such exciton blocking film improves the cell performance. It is shown that in the presence of Alq3 the forward bias adhered qualitatively to expectations for p–n junctions at the CuPc/C60 interface. Without this blocking exciton film, the analysis of the variation of the current with the forward bias shows that it fails to behave like a p–n junction. In this case it is shown that the current flow can be seen as nearly ohmic at low fields and close to space‐charge limited at higher fields. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inner‐shell photoabsorption spectroscopy of push–pull nitroanilines—Theoretical and experimental studies at N 1s region
Authors: Guerra Antonio C. O. , Ferreira Glaucio B. , Machado Sérgio P. , Turci Cássia C. 
Published: February 2008

AbstractOscillator strengths for N 1s excitation spectra of the gas‐phase aniline and nitrobenzene, and the solid‐phase meta‐ and para‐nitroanilines have been derived from the total electron yield and total ion yield spectra acquired by tunable synchrotron radiation. Ab initio calculations carried out within the improved virtual orbital method and equivalent ionic core virtual orbital model have been used to aid spectral interpretation. The Rydberg‐valency mixture has also been evaluated for all compounds. These results are compared to those acquired with the extended hückel molecular orbital method [Goeta et al., Chem Mater, 2000, 12, 3342]. The building block model has been used to simulate the nitroanilines spectra. The sensitivity of core excitation spectroscopy to intramolecular nitroanilines charge transfer and the N 1s → π* spectral features dependence upon the substitution pattern (meta or para) have been confirmed, as already verified for the gas‐phase inner‐shell energy loss spectra for the same molecules [Turci et al., Can J Chem, 1996, 74, 851]. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Stabilities, electronic properties of exohedral fluorine and trifluoromethyl derivatives for Td C28 fullerene C28F4–n(CF3)n (n = 0,1,2,3,4)
Authors: Tang Shu‐Wei , Chang Ying‐Fei , Sun Li‐Li , Sun Hao , Su Zhong‐Min , Wang Rong‐Shun 
Published: February 2008

AbstractABSTRACT:Stability and electronic property calculations are performed systematically based on density functional theory at the B3LYP/6‐31G(d) level for Td C28 fullerene and exohedral fluorine and trifluoromethyl derivatives C28F4–n(CF3)n (n = 0,1,2,3,4). All the exohedral derivatives that are on the potential energy surfaces are kinetically stable with large HOMO‐LUMO gaps. Further investigations show that binding energies of C28F4–n(CF3)n (n = 0,1,2,3,4) molecules are positive, suggesting they are thermodynamically stable. An analysis of the π‐orbital axis vector indicates the high strain in Td C28 cage could be greatly released by fluorine and trifluoromethyl decorations. Mulliken charge analysis reveals that adding different electron groups to the Td C28 cage can cause remarkably different charge populations. In addition, from the ionization potential and electron affinity investigations, the C28F4–n(CF3)n (n = 0,1,2,3,4) molecules manifest weak redox properties. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008