bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel dual‐mode square‐loop resonators using Hilbert perturbation for simultaneous size reduction and mode splitting
Authors: Liu Ji‐Chyun , Lu Po‐Chiang , Chang Jun‐Mao , Chien Chi‐Hsu , Kuei Ching‐Pin
Published: April 2007

The novel dual‐mode square‐loop resonator (DMSLR) with Hilbert perturbation is introduced to design bandpass filter in this paper. To obtain low insertion loss (0.55 dB), high out‐of‐band rejection level (−28.8 dB), and wider splitting band (BW 26.14%) filters, iterative Hilbert perturbation and space‐filling technique usage are proposed here. Significant size reduction of over 19% is obtained at 0.948 GHz. Results including surface current distributions and frequency responses are presented and discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1735–1739, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22503
Improving the radiation characteristics of a base station antenna array using a particle swarm optimizer
Authors: Zaharis Z. D. , Kampitaki D. G. , Lazaridis P. I. , Papastergiou A. I. , Hatzigaidas A. T. , Gallion P. B.
Published: April 2007

A particle swarm optimization based technique is applied on linear antenna arrays used by broadcasting base stations. Both the geometry and the excitation of the antenna array are optimized by a suitable algorithm under the constraints of the maximum possible gain at the desired direction and the desired value of side lobe level. The matching condition of the elements of the antenna array is also required by the algorithm. The technique has been applied to antenna arrays composed of collinear wire dipoles and seems to be very promising for improving radiation patterns of base station antenna arrays in many practical applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1690–1698, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22505
Design of high‐performance three‐strip 3‐DB directional coupler in multilayer technology with compensated parasitic reactances
Authors: Gruszczynski Slawomir , Wincza Krzysztof , Sachse Krzysztof
Published: April 2007

Recently developed technique of discontinuity effect compensation in coupled stripline directional couplers, regarding the connection of coupled and terminating signal lines, has been for the first time applied to the design of multilayer three‐strip 3‐dB directional couplers. Results of simulations and measurements are presented to confirm usefulness of the technique. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1656–1659, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22507
Holey fiber analysis employing FDM and FDTD methods on the transverse plane
Authors: Kim Jeong I.
Published: April 2007

Considering applicability to the analysis of holey fibers with random air‐hole arrangement on a transverse plane, finite‐difference time‐domain, and finite difference method (FDM) techniques are proposed to evaluate the transmission properties such as normalized propagation constant, chromatic dispersion, and effective area. Results are in remarkable agreement with the published data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1592–1594, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22511
Tolerance analysis of a PCS ceramic monoblock filter
Authors: Tsitsos S. , Kyriazidis P. , Gibson A. A. P.
Published: April 2007

Using an efficient equivalent circuit approach, the performance of a PCS ceramic monoblock filter under dimensional and material variations is thoroughly investigated. Graphs are used to understand how perturbations in the filter geometry affect the equivalent circuit and filter performance. It is noted that the critical tolerances are associated with the dielectric constant and resonator length. It follows that this method provides an efficient route to adjusting the filter design for a new specification without having recourse to costly electromagnetic solvers. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1759–1764, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22514
Design and characteristics of a small U‐slotted planar antenna for IR‐UWB
Authors: Vuong Tan‐Phu , Ghiotto Anthony , Duroc Yvan , Tedjini Smail
Published: April 2007

This article introduces the design of a small (30 mm × 35 mm × 1.6 mm) band‐rejected U‐slotted planar antenna on FR4 substrate having a relative permittivity of εr= 4.4 for Impulse Radio Ultra Wide Band (IR‐UWB) systems. The antenna is fed by a microstrip line and rejects the frequency band from 5.15 GHz to 5.825 GHz used by IEEE 802.11a and HIPERLAN/2. This antenna shows good characteristics for IR‐UWB. The effects of variation on steps and U‐Slot are discussed. The antenna is characterized both in the time and frequency domains by use of simulation and measurement.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1727–1731, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22515
An improved method of approaching impedance computation of probe fed ring resonator
Authors: Mahajan Madhurika , Chakravarty Tapas , Khah Sunil Kumar
Published: April 2007

In this article a new method of computation of input impedance of a probe‐fed ring resonator is presented. The method utilizes both cavity model and circuit theory to accurately predict the impedance of a high Q‐dominant mode resonance. Apart from accurate, this method can be generalized to predict impedance of first few modes of a probe‐fed ring resonator to reasonable accuracy. The computed result is compared with previously published data for TM12mode and discrepancies observed are listed. The method is also used to compute impedance for first few modes. For dominant mode, the numerical results are compared with IE3D results, which is a commercially available software based on method of moments. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1681–1684, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22518
Controllable metamaterial electrmagnetic structure research on applying to stealth technology
Authors: Xu Zhanxian , Lin Weigan , Kong Lidu
Published: April 2007

In this article, we present a new kind of a controllable metamaterial electromagnetic structure that it may be applied into stealth design and stealth technology in the future, in which the transmission coefficient of electromagnetic wave and single radar cross section (RCS) of structure are both electrically controlled, simulated, and characterized between 7 and 12 GHz. This structure is constructed with split ring resonators (SRRs) and metallic wire arrays including pin diodes, pin diodes are periodically inserted at these discontinuous each 10 mm to control the electrical continuity of the wires, and they can be either in an on state or in an off state depending on the voltage. the simulation and test prove that this structure could absorb electromagnetic incident wave, and have reduced RCS markedly with the largest scope of ‐6 dBm around frequency 9.0 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1616–1619, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22521
Experimental evaluation of indoor MIMO channel capacity for compact arrays of planar inverted‐F antennas
Authors: Carrasco Héctor , Feick Rodolfo , Hristov Hristo D.
Published: April 2007

Empirical results on indoor multiple input multiple output (MIMO) channel capacity obtained through the use of planar inverted‐F antennas (PIFA) are presented. An extensive statistical study done at 2.45 GHz reveals how antenna proximity and array configuration affects MIMO capacity. It is concluded that certain linear or square PIFA based arrays allow very compact multi‐antenna arrangements without significant capacity loss. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1754–1756, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22526
A very‐low‐profile broadband planar antenna for DCS‐1800 and IMT‐2000 applications
Authors: Li R. L. , Pan B. , Laskar J. , Tentzeris M. M.
Published: April 2007

A very‐low‐profile (VLP) broadband planar antenna is developed for DCS‐1800 and IMT‐2000 handsets. The VLP planar antenna consists of an S‐strip and a T‐strip, which are separately printed on the two sides of a thin substrate. The antenna height is only 4.8 mm which is much lower than previously published antenna configurations. The VLP planar antenna can achieve a bandwidth of ∼30% for return loss < ‐ 10 dB. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1679–1681, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22529
Using high permittivity ceramic substrates to fabricate a miniaturized bandpass filter with capacitive load
Authors: Huang Cheng‐Liang , Wang Jun‐Jie , Li Po‐Hsin
Published: April 2007

Using high permittivity ceramic substrates and capacitive coupling to miniaturize the sizes of Butterworth bandpass filters are investigated. The selectivity and stopband rejection of the designed filters can be improved significantly by utilizing a skew‐symmetric (zero degree) feed structure. These factors result in reducing the size of the filter. The responses of the Butterworth filters using Al2O3(εr= 10,Q × f= 20,000 GHz) and 0.85(Mg0.95Zn0.05)TiO3− 0.15Ca0.6La0.8/3TiO3(εr= 26,Q × f= 86,000 GHz) ceramic substrates are designed at a center frequency of 2.4 GHz. The compact size, low‐loss, sharp response, and performance of the filter are presented in this article. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1609–1613, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22533
Reshaping of picosecond optical pulses with a simple interferometer
Authors: Xianwei Zhou , Jianping Wang
Published: April 2007

In optical fiber communication systems, reshaping is crucial for long‐haul transmission and networks due to the accumulated noise and dispersion, which will gradually degrade the signals. In this article, a SOA (Semiconductor Optical Amplifier)‐based interferometer is proposed to realize all‐optical signal reshaping. Such scheme is known as advantageous for operation at high speed, which is analyst in theory. The distorted picosecond optical pulses train with repetition rate of 10 GHz is reshaped successfully in experiments employing this simple interferometer. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1606–1608, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22534
High‐coupling and ultra‐low‐loss interlaced stacked transformers for 60 100‐GHz CMOS RFIC applications
Authors: Lin Yo‐Sheng , Chen Chi‐Chen , Chen Chang‐Zhi , Yeh Po‐Feng
Published: April 2007

In this article, we demonstrate that high‐coupling and ultra‐low‐loss transformers for 60–100‐GHz CMOS RFIC applications can be achieved by using single‐turn two‐layer interlaced stacked (STIS) structure implemented in a standard CMOS technology. State‐of‐the‐art GAmaxof 0.711, 0.922, and ∼1 (i.e., NFminof 1.48, 0.35, and ∼0 dB) were achieved at 60, 80, and 100 GHz, respectively, for a STIS transformer with an inner dimension of 50 × 50 μm2and a metal width of 5 μm, mainly due to the high magnetic‐coupling factor and the high resistive‐coupling factor. In addition, a 94.1% (from 5.61 to 10.89) and a 196.8% (from 8.36 to 24.81) increase in Q‐factor, a 14.2% (from 0.711 to 0.812), and an 8.5% (from 0.922 to ∼1) increase in GAmax, and a 0.58 dB (from 1.48 to 0.90 dB) and a 0.35 dB (from 0.35 to ∼0 dB) decrease in NFminwere achieved at 60 and 80 GHz, respectively, for the transformer after the post‐process of proton implantation. The present analysis is helpful for RF engineers to design ultra‐low‐voltage high‐performance 60–100‐GHz transformer‐feedback CMOS (or BiCMOS) LNAs and VCOs, and other RF‐ICs which include transformers. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1750–1753, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22537
A Ku‐band three‐stage mmic low‐noise amplifier with superiorly low thermal‐sensitivity coefficients
Authors: Yu Shu‐Jenn , Hsu Wei‐Chou , Lee Ching‐Sung , Chang Chian‐Sern , Wu Chang‐Luen , Chang Ching‐Hsueh
Published: April 2007

A three‐stage monolithic microwave integrated‐circuit (MMIC) low‐noise amplifier (LNA) design with superiorly low thermal‐sensitivity coefficients in both the small‐signal gain and noise figure characteristics is reported. The amplifier is constituted by using the AlGaAs/GaAs pseudomorphic high electron mobility transistors (pHEMTs). It is suitable for the commercial applications at Ku‐band frequencies. Besides, a compact self‐biased structure with a single‐bias supply was employed to simplify the circuit and improve thermal stability. A noise figure of 2.3 dB with an associated gain of 22 dB is achieved at 16 GHz, and the output power, P1dB, is 17 dBm. The proposed LNA has demonstrated excellent thermal stability. The thermal‐sensitivity coefficients for the small‐signal gain and the noise figure are superiorly as low as 0.023 and 0.003 dB/°C, respectively, with respect to the temperature variation from −15 to 85°C. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1637–1641, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22543
An optical link for microwave clock distribution using optical carrier suppression and DC drift compensation
Authors: Onillon Bertrand , Danès Patrick , Bénazet Benoît , Llopis Olivier
Published: April 2007

Bias electrode DC drift of LiNbO3optical modulators becomes a critical problem when these devices operate over a long time period. This article presents a novel system of DC drift compensation for optical microwave transmissions using optical carrier suppression technique. In our case, such a system is dedicated to the optical distribution of high spectral purity microwave signals in future satellite payloads. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1634–1637, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22544
Compact semilumped elliptic‐function low‐pass filter using microstrip meander line
Authors: Lee Ju Gab , Lee Wu Seong , Ryu Jae Jong , Moon Yeon Kwan , Jang Joong Ho , Kim Ha Chul , Choi Hyun Chul
Published: April 2007

For the size reduction and sharp attenuation of the low‐pass filter in lower RF frequency range, a semilumped elliptic‐function low‐pass filter was proposed using microstrip meander line, chip capacitor, and radial stubs. To estimate more accurate inductance of microstrip meander line, it was modeled in an inhomogeneous dielectric environment, and then the calculated inductance was compared with the conventional case. To provide an additional attenuation pole in stop‐band, radial stubs were added to the proposed structure. The 3‐order low‐pass filter has a cutoff frequency of 1GHz and dimension of 14.6 × 16.3 mm2 on the substrate with a relative dielectric constant of 3.38. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1777–1779, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22545
Calculations of return loss of bonding wires fabricated on a test board by FDTD method
Authors: Chen Hsing‐Yi , Su Chieh‐Pin
Published: April 2007

Return losses of bonding wires fabricated on a test board for RF and microwave circuit applications are studied by the finite‐difference time‐domain (FDTD) method. Simulation results of return losses obtained by the FDTD method are presented and compared with those obtained by the HFSS software and measurements at frequencies of 0.04–6 GHz. It is found that simulation results calculated by the FDTD method make a good agreement with those obtained by the HFSS software. Results of the FDTD method are also further validated by the measurement data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1603–1606, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22546
Synovial fluid at microwave frequencies
Authors: Lonappan Anil , Thomas Vinu , Bindu G. , Rajasekaran C. , Mathew K. T.
Published: April 2007

Arthritis is one of the most pervasive diseases that causes of disability. For most people arthritis pain and inflammation cannot be avoided as the body ages. The present communication reports the study on the synovial fluid has the main lubricant in joints collected from normal persons and those ailing from arthritis are subjected to the microwave study and the variations of the dielectric parameters are investigated. The in vitro measurements of synovial fluid samples are done using cavity perturbation technique in the frequency range of 2–3 GHz. It is observed that in this band, the dielectric constant of normal samples are higher than those of arthritis affected ones and conductivity of is higher in normal samples, which finds application in detecting arthritis using microwaves. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1700–1702, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22552
A low‐profile planar antenna for DVB‐H terminals
Authors: Li R. L. , Pan B. , Laskar J. , Tentzeris M. M.
Published: April 2007

A low‐profile planar antenna has been developed for UHF‐band DVB‐H terminals. The antenna has a height of 8 mm and can be easily integrated with a printed circuit board. Through the exploitation of the electromagnetic coupling between a T‐strip and an S‐strip, the antenna can radiate efficiently over a wide frequency band. It has been demonstrated that the antenna can achieve a gain of −2 to −4 dBi over the DVB‐H band (470–702 MHz), which is 3–7 dB higher than the standard specification. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1630–1633, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22556
A simple K‐band waveguide‐to‐microstrip probe transition
Authors: Navarrini Alessandro , Pisanu Tonino , Mariotti Sergio , Idda Tonio
Published: April 2007

We describe the design, construction, and test of a simple K‐band waveguide‐to‐microstrip transition based on a radial‐shaped probe patterned on a quartz substrate. From 16 to 28 GHz, the measured reflection coefficient at the coaxial SMA input, used for test purposes of the adapter, was less than −14 dB, and the dissipative loss was ∼0.30 dB. The estimated loss of the waveguide to microstrip transition only, with coaxial connector effects removed, is ∼0.08 dB. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1597–1600, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22558
A low‐noise UWB cmos mixer using current bleeding and resonant inductor techniques
Authors: Jung Goo‐Young , Shin Jae‐Hoon , Yun Tae‐Yeoul
Published: April 2007

This article presents a direct down‐conversion mixer for ultra‐wideband systems on 0.18 μm RF CMOS process. The proposed mixer uses a current bleeding technique and an internal resonant inductor to improve the conversion gain and noise figure of the conventional Gilbert‐cell mixer. Effects of each technique are compared on mixer's noise performance. Measured results show the conversion gain of 7.5–10.1 dB and the double side‐band noise figure of 8.8–12.5 dB at Band 1 (3.168–3.696 GHz) and the gain of −1.4 to 1.6 dB and the double side‐band noise figure of 12.2–17.6 dB at Band 13 (9.768–10.296 GHz). The circuit operates at the supply voltage of 1.8 V and dissipates 13.24 mW. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1595–1597, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22559
Dynamic data‐driven finite element models for laser treatment of cancer
Authors: Oden J.T. , Diller K.R. , Bajaj C. , Browne J.C. , Hazle J. , Babuška I. , Bass J. , Biduat L. , Demkowicz L. , Elliott A. , Feng Y. , Fuentes D. , Prudhomme S. , Rylander M. N. , Stafford R.J. , Zhang Y.
Published: April 2007

Elevating the temperature of cancerous cells is known to increase their susceptibility to subsequent radiation or chemotherapy treatments, and in the case in which a tumor exists as a well‐defined region, higher intensity heat sources may be used to ablate the tissue. These facts are the basis for hyperthermia based cancer treatments. Of the many available modalities for delivering the heat source, the application of a laser heat source under the guidance of real‐time treatment data has the potential to provide unprecedented control over the outcome of the treatment process (McNichols et al., Lasers Surg Med 34 (2004), 48–55; Salomir et al., Magn Reson Med 43 (2000), 342–347). The goals of this work are to provide a precise mathematical framework for the real‐time finite element solution of the problems of calibration, optimal heat source control, and goal‐oriented error estimation applied to the equations of bioheat transfer and demonstrate that current finite element technology, parallel computer architecture, data transfer infrastructure, and thermal imaging modalities are capable of inducing a precise computer controlled temperature field within the biological domain. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 23: 904–922, 2007
Reliability of computational science
Authors: Babuška I. , Nobile F. , Tempone R.
Published: April 2007

Today's computers allow us to simulate large, complex physical problems. Many times the mathematical models describing such problems are based on a relatively small amount of available information such as experimental measurements. The question arises whether the computed data could be used as the basis for decision in critical engineering, economic, and medicine applications. The representative list of engineering accidents occurred in the past years and their reasons illustrate the question. The paper describes a general framework for verification and validation (V&V) which deals with this question. The framework is then applied to an illustrative engineering problem, in which the basis for decision is a specific quantity of interest, namely the probability that the quantity does not exceed a given value. The V&V framework is applied and explained in detail. The result of the analysis is the computation of the failure probability as well as a quantification of the confidence in the computation, depending on the amount of available experimental data. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 23: 753–784, 2007
Proteomic analysis of photosystem I components from different plant species
Authors: Zolla Lello , Rinalducci Sara , Timperio Anna Maria
Published: April 2007

In this study, the photosystem I (PSI) highly hydrophobic proteins present within stroma lamellae of the thylakoid membrane were separated by RP‐HPLC and identified either by in‐solution trypsin digestion peptide fragment fingerprinting or by the close correspondence between the intact mass measurements (IMMs) and those expected from the DNA sequence. Protein identification performed by MS/MS was as reliable as IMMs. Thus, IMM is an easy and valid method for identifying proteins that have no PTMs. This paper reports the Mr for all PSI proteins in ten different species, including those whose genes have not yet been cloned. Lhca5 was revealed unequivocally in four species, corroborating that it is indeed a protein belonging to the light‐harvesting antenna of PSI. In all species examined, the product of the Lhca6 gene has never been revealed. Concerning core proteins, Psa‐O has been revealed in three species; isoforms of Psa‐D and Psa‐E have been found in both monocots and dicots. Small proteins like Psa‐I and Psa‐J are well separated and identified. RP‐HPLC produces reliable fingerprints and reveals that the relative amounts of PSI proteins appear to be markedly different.
Toward a better analysis of secreted proteins: the example of the myeloid cells secretome
Authors: Chevallet Mireille , Diemer Hélène , Van Dorssealer Alain , Villiers Christian , Rabilloud Thierry
Published: April 2007

The analysis of secreted proteins represents a challenge for current proteomics techniques. Proteins are usually secreted at low concentrations in the culture media, which makes their recovery difficult. In addition, culture media are rich in salts and other compounds interfering with most proteomics techniques, which makes selective precipitation of proteins almost mandatory for a correct subsequent proteomics analysis. Last but not least, the non‐secreted proteins liberated in the culture medium upon lysis of a few dead cells heavily contaminate the so‐called secreted proteins preparations. Several techniques have been used in the past for concentration of proteins secreted in culture media. These techniques present several drawbacks, such as coprecipitation of salts or poor yields at low protein concentrations. Improved techniques based on carrier‐assisted TCA precipitation are described and discussed in this report. These techniques have been used to analyze the secretome of myeloid cells (macrophages, dendritic cells) and enabled to analyze proteins secreted at concentrations close to 1 ng/mL, thereby allowing the detection of some of the cytokines (TNF, IL‐12) secreted by the myeloid cells upon activation by bacterial products.
The contribution of attachment security and social support to depressive symptoms in patients with metastatic cancer
Authors: Rodin Gary , Walsh Andrew , Zimmermann Camilla , Gagliese Lucia , Jones Jennifer , Shepherd Frances A. , Moore Malcolm , Braun Michal , Donner Allan , Mikulincer Mario
Published: April 2007

The present study examines the association between disease‐related factors, perceived social support, attachment security (i.e. attachment anxiety and avoidance), and the occurrence of depressive symptoms in a sample of patients with metastatic gastrointestinal or lung cancer. Results from a sample of 326 cancer outpatients with advanced disease indicate that disease‐related factors are significantly associated with the occurrence of depressive symptoms, and the latter are inversely related to the degree of attachment anxiety and avoidance, and perceived social support. Attachment security (on the dimension of anxious attachment) significantly buffered the effect of disease‐related factors on depressive symptoms, and perceived social support mediated the relationship between attachment security and depressive symptoms. The buffering effect of attachment security on depressive symptoms and its partial mediation through social support suggest that the interaction of individual, social, and disease‐related factors contribute to the emergence of depressive symptoms in patients with metastatic cancer. Copyright © 2007 John Wiley & Sons, Ltd.
Thermoelectric effects in STM tunneling through a monoatomic chain
Authors: Krawiec M. , Jałochowski M.
Published: April 2007

We study thermoelectric properties of the system composed of a monoatomic chain on a surface and additional electrode coupled to the chain, which can be an STM tip. In particular, we are interested in thermopower, electric and thermal conductance, Wiedemann–Franz relation and thermoelectric figure of merit, which is a direct measure of the usefulness of the system for applications. We discuss the modifications of the STM wire topography due to temperature difference between the electrodes. Finally, we also make connection to STM experiment, in which the thermopower has been directly measured, showing different structure, not visible in topography spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bottom‐up approach to high‐temperature superconductivity
Authors: Won Hyekyung , Haas Stephan , Maki Kazumi
Published: April 2007

Since the discovery of high‐temperature superconductivity in the cuprates a theoretical understanding of their phase diagram has remained one of the major outstanding problems in condensed matter physics. Here we propose an effective low‐energy Hamiltonian which produces both d‐wave density wave (dDW) and d‐wave superconducting (dSC) solutions within the BCS mean‐field theory. This model predicts that (a) the observed pseudogap phase is a dDW state, (b) the superconducting phase is a d‐wave BCS state, and (c) in the underdoped regime there is a gossamer superconducting state, i.e. dSC in coexistence with dDW. Moreover, this theory naturally explains the Uemura relation, the reduction of the quasiparticle density of states at the Fermi level, and the salient features in the tunneling conductivity measured in underdoped Bi2212. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shell structures and electron‐spin configurations in single‐walled carbon nanotube quantum dots
Authors: Moriyama S. , Fuse T. , Ishibashi K.
Published: April 2007

We have carried out low‐temperature transport measurements in individual carbon nanotube quantum dots. Two‐ and four‐electron shell structures have been carefully investigated, and the magnetic field evolution of the single‐electron transport spectroscopy has revealed the electron‐spin configurations in the dot. Our experimental results reveal that the carbon nanotube quantum dot is an artificial atom that exhibits shell filling and is the simplest example of the Hund's rule. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effective‐site percolation approach in two dimensions
Authors: Pawłowski G.
Published: April 2007

A new Monte Carlo cluster approach to describe the order–order and order–disorder transitions in two‐dimensional (2D) correlated systems is presented. It is shown that a phase transition of a physical system can be correctly described in terms of the percolation language of the effective‐site approach. In contrast to the well‐known bond approaches, the method proposed does not require additional assumptions as to the acceptance of the bonds. The new idea is based on the site approach to elementary ordered plaquettes, leading to the accurate coincidence of percolation and the phase transitions in 2D. Here I present the analysis of the spin‐system in the Blume–Capel model and the charged‐system in the atomic limit of the extended Hubbard model. In both cases the interpretation of the phase transition is made in terms of the percolation of different types of order. The new method allows precise identification of the pure and mixed phases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tight binding analogue of cyclotron orbits
Authors: Wal A.
Published: April 2007

The magnetic translation group describes the symmetry of the itinerant electron on two‐dimensional lattice with perpendicular magnetic field. For such a finite system, with periodic condition the properties of the irreducible representations of this group are responsible for the tight‐binding analogue of cyclotron orbits of the free electron case. The relation between the size of the planar lattice and the structure of the group and its irreducible representations is pointed out. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic phase diagram of the anisotropic multi‐band Hubbard model
Authors: van Dongen P. G. J. , Knecht C. , Blümer N.
Published: April 2007

Using quantum Monte Carlo (QMC) simulations we determine the magnetic phase diagram of the anisotropic two‐band Hubbard model within the dynamical mean‐field theory (DMFT) in the important intermediate‐coupling regime. We compare the QMC predictions with exact results from second‐order weak‐ and strong‐coupling perturbation theory. We find that the orbital‐selective Mott transition (OSMT), which occurs in the fully frustrated case, is completely hidden in the antiferromagnetic (AF) ground state of the model. On the basis of our results, we discuss possible mechanisms of frustration. We also demonstrate the close relationship of the physics of the two‐band Hubbard model in the orbital‐selective Mott (OSM) phase to the Falicov–Kimball model. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fibre structure of a model manifold of classical configuration space in Bethe ansatz
Authors: Milewski J. , Lulek B. , Lulek T.
Published: April 2007

Within Bethe ansatz approach, the system of r Bethe pseudoparticles on a magnetic ring of N nodes is characterised by a finite set of magnetic configurations which can be interpreted as a classical configuration space. This space can be embedded into r ‐dimensional manifold. Here we present the fibre bundle structure of this model manifold. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ergot alkaloids in Norwegian wild grasses: a mass spectrometric approach
Authors: Uhlig Silvio , Vikøren Turid , Ivanova Lada , Handeland Kjell
Published: April 2007

Ergot alkaloids are mycotoxins which are produced among fungi in the family Clavicipitaceae. Poisoning with ergot alkaloids is an important veterinary problem in animal husbandry and has recently also been recognised in wild animals. While the poisoning syndrome observed in domestic animals such as cattle, horses and sheep is usually caused by endophyte‐infected grass, the recently observed ergotism among Norwegian cervids is probably due to infection of wild grasses with Claviceps. Mass spectrometry is today the method of choice for the rapid qualitative and quantitative determination of many natural compounds. This study uses tandem quadrupole mass spectrometry as well as ion trap mass spectrometry in connection with electrospray(+) ionisation for the quantification, screening and fragmentation of ergot alkaloids in extracts from Claviceps sclerotia that had been picked from wild grasses from several locations in Norway. Ergotamine, ergovaline, ergonovine and ergocryptine were available as standards and were quantified in the extracts, while ergocrystine, ergocornine, ergonine/ergosine, lysergic acid and lysergol were identified on the basis of their molecular weights and semi‐quantified. Ergocrystine dominated the alkaloid spectrum of most extracts. Levels of the quantified alkaloids were in the range 0.2–9300 µg/g. Several unknown ergot alkaloids were found in the extracts. MSn experiments identified some as simple lysergic acid amide derivatives, while othes are probably related to ergocrystine and ergocryptine by dehydration, dehydrogenation and/or amino acid substitution at R1 of the peptide moiety. Copyright © 2007 John Wiley & Sons, Ltd.
A method for testing the significance of geographical correlations with application to industrial lung cancer in France
Authors: Richardson Sylvia
Published: April 2007

This paper discusses some of the problems encountered when testing significance in geographical epidemiology where variables typically exhibit some spatial autocorrelation. A test of partial correlation between spatially autocorrelated variables is presented. It is based on evaluation of an effective sample size which takes account of spatial structure. Performance is assessed by Monte Carlo simulation. The proposed method is used to study male lung cancer rates in specific industries in France.
Maximum likelihood estimation of reference centiles
Authors: Thompson M. L. , Theron G. B.
Published: April 2007

We propose the use of centile estimates which are based on the fitting of appropriate densities by maximum likelihood. In the case of cross‐sectional centile estimation, we show that this approach will generally lead to more precise estimates than would result from the use of non‐parametric centile estimates. When longitudinal data are available or a series of cross‐sectional data at different time points, the maximum likelihood approach can be used to simultaneously fit densities to each cross‐section, subject to constraints (for example, smoothness constraints) on the parameters. The variances of these centile estimates are readily obtained and missing values and unequally spaced records are easily accommodated. We illustrate the procedure by means of an application using the Johnson family of densities to a study of weight gain in pregnancy.
Outlier detection in bioavailability/bioequivalence studies
Authors: Chow Shein‐Chung , Tse Siu‐Keung
Published: April 2007

This paper concerns techniques for detection of a potential outlier or extreme observation in a bioavailabi1ity/bioequivalence study. A bioavailability analysis that includes possible outlying values may affect the decision on bioequivalence. We consider a general crossover model that takes into account period and formulation effects. We derive two test procedures, the likelihood distance and the estimates distance, to detect potential outliers. We show that the two procedures relate to a chi‐square distribution with three degrees of freedom. The main purpose of this paper is to exhibit and discuss these two general approaches of outliers detection in the context of a bioavailability/bioequivalence study. To illustrate these approaches, we use data from three‐way crossover experiment in the pharmaceutical industry that concerned the comparison of the bioavailability of two test formulations and a standard (reference) formulation of a drug. This example demonstrates the influence of an outlying value in the study of bioequivalence.
Latent class analysis of diagnostic agreement
Authors: Uebersax John S. , Grove William M.
Published: April 2007

We describe methods based on latent class analysis for analysis and interpretation of agreement on dichotomous diagnostic ratings. This approach formulates agreement in terms of parameters directly related to diagnostic accuracy and leads to many practical applications, such as estimation of the accuracy of individual ratings and the extent to which accuracy may improve with multiple opinions. We describe refinements in the estimation of parameters for varying panel designs, and apply latent class methods successfully to examples of medical agreement data that include data previously found to be poorly fitted by two‐class models. Latent class techniques provide a powerful and flexible set of tools to analyse diagnostic agreement and one should consider them routinely in the analysis of such data.
Randomized consent designs for clinical trials: An update
Authors: Zelen M.
Published: April 2007

Randomized consent designs were introduced to make it easier for physicians to enter patients in randomized clinical trials. Physician reluctance to participate in randomized clinical trials is often a reflection that the physician‐patient relationship could be compromised if the physician makes known to the patient his/her inability to select a preferred therapy. Clinical trials having a no‐treatment control or placebo amplify this concern. This paper reviews the main ideas of randomized consent designs (single and double) and the statistical model underlying the analysis, and presents some recent experiences.
Time from infection with HIV to onset of AIDS in patients with haemophilia in the UK
Authors: Darby S. C. , Doll R. , Thakrar B. , Rizza C. R. , Cox D. R.
Published: April 2007

The two‐stage parametric regression model of Brookmeyer and Goedert has been adapted and fitted to data on the development of AIDS in haemophiliacs in the UK who are seropositive for HIV. The risk of developing AIDS by a given time following seroconversion increases with increasing age at seroconversion. It is likely that the risk increases smoothly with age, although the data have been analysed in three age categories, and it is estimated that by seven years after seroconversion 6 per cent of patients aged under 25 at seroconversion, 20 per cent of those aged 25–44 and 34 per cent of those aged 45 or more have developed AIDS. For a given age at seroconversion the annual risk of developing AIDS increases with increasing time after seroconversion, and at seven years the annual risks of developing AIDS during the next year in the three age groups are estimated to be 2 per cent for those aged less than 25 at seroconversion, and 10 and 11 per cent respectively for those aged 25–44 and 45 or more.
An application of density estimation to geographical epidemiology
Authors: Bithell J. F.
Published: April 2007

A relative risk function over a geographical region is defined and it is shown that it can be estimated effectively using kernel density estimation separately for the spatial distribution of disease cases and for a sample of controls. This procedure is demonstrated using data on childhood leukaemia in the vicinity of the Sellafield nuclear reprocessing plant in Cumbria, U.K. Various modifications to the method are proposed, including the use of an adaptive kernel. The final plot demonstrates a sharp peak at Sellafield and a reasonably smooth surface over the rest of the region, despite the small number of cases in the series.
Statistical analysis of quality of life data in cancer clinical trials
Authors: Olschewski M. , Schumacher M.
Published: April 2007

In clinical trials endpoints other than total and/or disease‐free survival are gaining more and more interest. In particular, quality of life (QOL) or the well‐being of patients has emerged as a synonym for variables describing the subjective reactions of patienis towards their disease and its treatment. The statistical analysis of such QOL data is complicated firstly by the large number of variables measured and their obvious lack of objectivity. The construction of suitable aggregate measures allowing a reduction of the measurements into a (preferably) unidimensional index are discussed in the context of an analysis at a fixed time point during the course of treatment. A second problem arises from the consideration that a patient's well‐being is subject to changes over time. We discuss the modelling of QOL by suitable stochastic processes which are extensions of a multistate disease process. This allows QOL events to be incorporated into methods of survival analysis by either estimating the relevant transition probabilities between states or calculating quality‐adjusted survival times. Finally, some brief guidelines for the planning of clinical trials including QOL measurements will be proposed.
Applications of global statistics in analysing quality of life data
Authors: Tandon P. K.
Published: April 2007

Quality of life (QOL) instruments usually consist of a number of components, each of which deals specifically with a particular functionally related dysfunction. In a clinical trial whose primary aim is the evaluation of the treatment by means of QOL instruments, analysis of each of the components usually consists of either univariate analysis of variance (ANOVA) or some non‐parametric methods. This multiple testing approach can produce an increase in false positive findings. One attempt to correct for this is the Bonferroni adjustment. Another approach is to apply global statistics (parametric or non‐parametric) for the null hypothesis of no treatment difference versus the alternative hypothesis that one treatment is uniformly better than the other for QOL instruments as a whole.

Data from a randomized double‐blind trial of 111 congestive heart failure patients, which involved four QOL instruments, were analysed with univariate ANOVA, Bonferroni adjustment, parametric and non‐parametric global statistics. The global statistics complemented the univariate methods and made the presentation of QOL data very effective. I recommend the general use of global statistics in analysis of QOL data.
A two‐step method for understanding and fitting growth curve models
Authors: Stanek Edward J.
Published: April 2007

With data from a repeated measures design, analysts often overlook growth curve analysis based on the Potthoff‐Roy model. The reluctance to perform a growth analysis may result partially from unfamiliarity with the technique, and partially from the lack of readily available computational programs to fit the models. Although growth curve analysis has traditionally appeared as a special technique in multivariate analysis, one can fit the models with the use of two simple ideas: transformation of variables, and weighted least squares (WLS). When presented in this manner, growth models are a natural extension of univariate repeated measures models. Growth curve analyses share with univariate analyses the common objective to limit estimation to a parsimonious set of parameters that characterize the response profiles. One can readily fit models with commonly available software. The two‐step methodology also allows the fit of more general growth models that are appropriate when groups have different shape profiles. Two examples illustrate this approach to growth curve analysis.
Historical and methodological developments in clinical trials at the national cancer institute
Authors: Gehan Edmund A. , Schneiderman Marvin A.
Published: April 2007

The first randomized clinical trial at the National Cancer Institute (NCI), planned in 1954, commenced in 1955 for the treatment of patients with acute leukaemia. The programme in clinical trials at NCI had strong influence from the clinician and administrator, C. Gordon Zubrod, who introduced the randomized clinical trial at NCI and organized the co‐operative clinical trials programme of the Cancer Chemotherapy National Service Center (CCNSC) beginning about 1955. The biostatistician, Marvin Schneiderman, collaborated on the first randomized trials in acute leukaemia and solid tumours and recruited the biostatisticians and statistical centres in the early phase of the co‐operative clinical trials programme of the CCNSC. From the beginning, there was acceptance of the principles of the randomization of patients and the statistical analysis of data. The sequence of clinical trials for a new agent included the non‐randomized phase I (dosage finding) and phase II (preliminary efficacy) trials as well as the phase III (comparison of treatments) trials. New concepts for the treatment of patients developed from 1955 to the mid‐1960s included the combination of therapies with independent activity to increase response rates and the administration of therapy to patients in a disease‐free (remission) state to prolong the disease‐free state. Methodological developments related to clinical trials up to the mid‐1960s included: a plan for phase II trials (Gehan10); a generalization of the Wilcoxon test for the comparison of survival distributions with right‐censored data (Gehan25); a test of proportional hazards for survival distributions, which later became known as the Mantel‐Haenszel test (Mantel38), and an exponential regression model with an explanatory variable (Feigl and Zelen41).
Application of the triangular test to phase II cancer clinical trials
Authors: Bellissant Eric , Benichou Jacques , Chastang Claude
Published: April 2007

Phase II cancer clinical trials are primarily designed to determine whether the response rate p to the treatment under study is greater than a specified value p0, that is to test the null hypothesis H0: p < p0 against an alternative hypothesis H1: p > p0 specified by p = p1. As an alternative to the single and multistage procedures and to Wald's continuous sequential probability ratio test (SPRT), we applied the group sequential methods proposed by Jones and Whitehead, namely the triangular test (TT) and the discrete SPRT, to the comparison of p with p0, and we expressed H0 and H1 in terms of the log odds‐ratio statistic log [p(1 — p0)/Po(1 — p)]. A simulation study showed that both the TT and the discrete SPRT had type I error and power close to the nominal values, and they compared favourably with multistage methods in terms of the average sample size.