bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging of optical field confinement in ridge waveguides fabricated on very-small-aperture laser
Authors: Chen Fang , Itagi A. , Bain J. A. , Stancil D. D. , Schlesinger T. E. , Stebounova L. , Walker G. C. , Akhremitchev B. B.
Published: October 2003

Optical field confinement in a ridge waveguide nanostructure (“C” aperture) designed for ultrahigh-density recording was observed using an apertureless near-field scanning optical microscope. The aperture was fabricated on a commercial edge-emitting semiconductor laser as the light source. High-contrast near-field images at both 1× and 2× lock-in detection frequencies were obtained. The emission patterns are in agreement with theoretical simulation of such structures. A 90 nm×70 nm full width half maximum spot size was measured and is comparable to the ridge width of the aperture.
Implantation-induced electrical isolation of GaAsN epilayers grown by metalorganic chemical vapor deposition
Authors: Gao Q. , Deenapanray P. N. K. , Tan H. H. , Jagadish C.
Published: October 2003

The electrical isolation of p-type GaAs1−xNx epilayers (x=0.6%, 1.4%, and 2.3%) produced by H, Li, C, or O ion implantation and its thermal stability in nominally undoped GaAs0.986N0.014 epilayers were investigated. Results show that the sheet resistance of p-type GaAsN layers can be increased by about five or six orders of magnitude by ion implantation and the threshold fluence (Fth) to convert a conductive layer to a highly resistive one depends on the original free carrier concentration and the number of implantation-generated atomic displacements, and does not depend on the nitrogen content. The thermal stability of electrical isolation in GaAsN depends on the ratio of the final fluence to the threshold fluence. The electrical isolation can be preserved up to 550 °C when the accumulated fluence is above 3.3 Fth.
Melting behavior of levitated Y2O3
Authors: Hennet L. , Thiaudière D. , Landron C. , Melin P. , Price D. L. , Coutures J.-P. , Bérar J.-F. , Saboungi M.-L.
Published: October 2003

The yttrium environment in liquid Y2O3 at 2770 K has been measured with anomalous x-ray scattering, aerodynamic levitation, and laser heating. The Y–O coordination of 6–7 and the Y–Y coordination of around 12 imply that the close packing of the high-temperature (H-type) solid phase is preserved on melting, in contrast to the large structural changes exhibited by Al2O3. The unusually sharp main diffraction peak implies a high degree of chemical order and mirrors the diffraction pattern of the H-type phase.
Negative luminescence with 93% efficiency from midwave infrared HgCdTe diode arrays
Authors: Bewley W. W. , Lindle J. R. , Vurgaftman I. , Meyer J. R. , Johnson J. L. , Thomas M. L. , Tennant W. E.
Published: October 2003

We have investigated the negative luminescence (NL) properties of an array of HgCdTe photodiodes (λco=4.6 μm at 295 K) as a function of temperature and wavelength. The internal NL efficiency of ≈93% at λ=4.0 μm is nearly independent of temperature in the 240–300 K range, and at 296 K corresponds to an apparent temperature reduction of 54 K. This is obtained at a reverse-bias saturation current density of only 0.13 A/cm2 at 296 K, which is attributable in part to an array geometry that reduces the influence of macroscopic defects. These observed NL performance characteristics are compatible with most of the requirements for applications such as cold shielding.
Measurement of the Auger recombination rate in p-type 0.54 eV GaInAsSb by time-resolved photoluminescence
Authors: Anikeev S. , Donetsky D. , Belenky G. , Luryi S. , Wang C. A. , Borrego J. M. , Nichols G.
Published: October 2003

Auger recombination in p-type GaSb, InAs, and their alloys is enhanced due to the proximity of the band gap energy and the energy separation to the spin split-off valence band. This can affect the device performance even at moderate doping concentration. We report electron lifetime measurements in a p-type 0.54 eV GaInAsSb alloy, commonly used in a variety of infrared devices. We have studied a series of double-capped heterostructures with varied thicknesses and doping levels, grown by organometallic vapor phase epitaxy on GaSb substrates. The Auger coefficient value of 2.3×10−28 cm6/s is determined by analyzing the photoluminescence decay constants with a systematic separation of different recombination mechanisms.
Light-driven microcantilever actuator based on photoenhanced magnetization in a GaAs–Fe composite film
Authors: Shinshi Tadahiko , Kato Fumihito , Shimokohbe Akira , Noguchi Hiroshi , Munekata Hiroo
Published: October 2003

Using the recently discovered phenomenon of photoenhanced magnetization in GaAs–Fe semiconductor-ferromagnet composite films [S. Haneda, S. Koshihara, and H. Munekata, Physica E 10, 437 (2001)], we have demonstrated a light-driven microactuator. It consists of a GaAs–Fe/GaAs(100) chip glued onto a 4.3 mm long, 2.1-μm-thick Si cantilever. A deflection of 0.7 μm was achieved when the cantilever was illuminated with 650 nm, 713 μW laser light in a magnetic field of 1.7 T at room temperature.
Electrical and optical properties of Fe-doped semi-insulating GaN templates
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Pearton S. J.
Published: October 2003

Electrical and optical properties of semi-insulating GaN films with the lower part of the film doped with Fe were studied. The room-temperature sheet resistivity of the films was found to be 2×1010 Ω/square. The activation energy of the dark conductivity was ∼0.5 eV which corresponds to the depth of the dominant electron traps pinning the Fermi level. The concentration of these traps was highest in the Fe-doped portion of the films and was on the order of 3×1016 cm−3. Photoinduced current transient spectroscopy also showed the presence of a high concentration of deeper electron traps with level at EC−0.9 eV and hole traps at EV+0.9 eV. These layers look very promising as insulating buffers for AlGaN/GaN transistor structures.
Fabrication and magnetic properties of ultrathin Fe nanowire arrays
Authors: Zhang X. Y. , Wen G. H. , Chan Y. F. , Zheng R. K. , Zhang X. X. , Wang N.
Published: October 2003

Ultrathin Fe nanowire (about 5 nm in diameter) arrays have been fabricated by electrodeposition using anodic porous alumina templates. These ultrathin nanowires exhibited uniaxial anisotropy and a quite large coercivity (4190 Oe) at 5 K. In addition, the field needed to saturate the magnetization, when the field was applied perpendicularly to the easy axis, was much larger than the shape anisotropy field (2πMS). This saturation field increased with decreasing temperature. We believed that this enhanced saturation field was mainly due to the contribution of the surface spins.
Neutron emission from a fast plasma focus of 400 Joules
Authors: Silva Patricio , Moreno José , Soto Leopoldo , Birstein Lipo , Mayer Roberto E. , Kies Walter
Published: October 2003

The neutron emission from a small and fast plasma focus operating in deuterium is presented. The system operates at low energy in the hundred of joules range (880 nF capacitor bank, 38 nH, 20–35 kV, 176–539 J, ∼300 ns current rise time). The neutrons were measured by means of a silver activation counter, and the total neutron yield versus deuterium gas filling pressure was obtained. For discharges operating at 30 kV charging voltage, the maximum neutron yield was (1.06±0.13)×106 neutrons per shot at 9 mbar.
Magnetic tunnel junctions with yttrium oxide barrier
Authors: Dimopoulos T. , Gieres G. , Colis S. , Wecker J. , Luo Y. , Samwer K.
Published: October 2003

Magnetic tunnel junctions have been studied, with YOx barriers prepared by plasma oxidation of a 1.5 nm Y film. We report their junction area resistance, tunnel magnetoresistance (TMR) and barrier parameters (height and thickness) as a function of the oxidation time. For the optimum oxidation time, TMR values of ∼25% are obtained at room temperature and ∼44% at low temperature (5 K). The barrier height extracted from the current–voltage curves, is close to 1 eV, which is less than half of what is usually reported for AlOx-based junctions. Structural and topographical characterization of the multilayes revealed that the YOx layer is amorphous with well-defined, smooth, and correlated interfaces with the ferromagnetic electrodes.
Ga-doped ZnO single-crystal nanotips grown on fused silica by metalorganic chemical vapor deposition
Authors: Zhong J. , Muthukumar S. , Chen Y. , Lu Y. , Ng H. M. , Jiang W. , Garfunkel E. L.
Published: October 2003

In situ Ga-doped ZnO nanotips were grown on amorphous fused silica substrates using metalorganic chemical vapor deposition. Structural, optical, and electrical properties of as-grown ZnO nanotips are investigated. Despite the amorphous nature of fused silica substrates, Ga-doped ZnO nanotips are found to be single crystalline and oriented along the c-axis. Photoluminescence (PL) spectra of Ga-doped ZnO nanotips are dominated by near-band-edge emission with negligible deep-level emission. The increase in PL intensity from Ga doping has been attributed to the increase of Ga donor-related impurity emission. Current–voltage characteristics of the ZnO nanotips are measured by conductive-tip atomic force microscopy, which shows the conductivity enhancement due to Ga doping.
Crossover between nucleation-controlled kinetics and domain wall motion kinetics of polarization reversal in ferroelectric films
Authors: Stolichnov I. , Tagantsev A. , Setter N. , Cross J. S. , Tsukada M.
Published: October 2003

The study of polarization reversal in (Pb,La)(Zr,Ti)O3 thin films reveals a drastic difference between the switching kinetics observed at RT and at low temperature of 40 K. In particular, at 40 K, the switching kinetics in studied films is similar to that observed in ferroelectric single crystals. Additionally, the films with completely different switching behavior at RT show very similar switching properties at 40 K. The data analysis suggests that the polarization reversal at RT is limited mainly by nucleation of reversed domains, while at 40 K, the switching kinetics is governed by domain wall motion. It is demonstrated that the measurements of switching kinetics at low temperature can provide useful information for modeling of the important, practical case of polarization reversal at RT.
Coercive field of ultrathin Pb(Zr0.52Ti0.48)O3 epitaxial films
Authors: Pertsev N. A. , Rodrı́guez Contreras J. , Kukhar V. G. , Hermanns B. , Kohlstedt H. , Waser R.
Published: October 2003

The polarization reversal in single-crystalline ferroelectric films has been investigated experimentally and theoretically. The hysteresis loops were measured for Pb(Zr0.52Ti0.48)O3 films with thicknesses ranging from 8 to 250 nm. These films were grown epitaxially on SrRuO3 bottom electrodes deposited on SrTiO3 substrates. The measurements using Pt top electrodes showed that the coercive field Ec increases drastically as the film becomes thinner, reaching values as high as Ec≈1200 kV/cm. To understand this observation, we calculated the thermodynamic coercive field Eth of a ferroelectric film as a function of the misfit strain Sm in an epitaxial system and showed that Eth strongly depends on Sm. However, the coercive field of ultrathin films, when measured at high frequencies, exceeds the calculated thermodynamic limit. Since this is impossible for an intrinsic coercive field Ec, we conclude that measurements give an apparent Ec rather than the intrinsic one. An enormous increase of apparent coercive field in ultrathin films may be explained by the presence of a conductive nonferroelectric interface layer.
Decomposition of interfacial SiO2 during HfO2 deposition
Authors: Copel M. , Reuter M. C.
Published: October 2003

Growth of HfO2 by Hf deposition in an oxidizing ambient is found to cause removal of interfacial SiO2. Medium-energy ion scattering results show that the reaction takes place during growth, and involves transport of oxygen through the HfO2 layer. An examination of the temperature dependence suggests that oxygen vacancy reactions are responsible.
Evidence for two-phase regions in Ba0.5Sr0.5TiO3 thin films from capacitance–voltage data
Authors: Jiang A. Q. , Scott J. F. , Sinnamon L. J. , Gregg J. M.
Published: October 2003

The Curie–Weiss plots of reciprocal dielectric constant versus temperature, in Ba0.5Sr0.5TiO3 films grown onto SrRuO3 lower electrodes by pulsed-laser deposition, show two minima below film thicknesses of 280 nm. This double minima implies possible mixed phases in the thin films. A graphical plot of capacitance for decreasing dc voltage versus that of increasing dc voltage shows a well-defined triangular shape for both Pb(Zr0.4Ti0.6)O3 and SrBi2Ta2O9 thin films. However, for a 175-nm-thick Ba0.5Sr0.5TiO3 thin film, the plot shows an overlapping of two triangles, suggesting mixed phases. This graphical method appears to be effective in detecting structural subtleties in ferroelectric capacitors.
Bends and splitters for self-collimated beams in photonic crystals
Authors: Yu Xiaofang , Fan Shanhui
Published: October 2003

We present finite-difference time-domain studies for self-collimated beams in photonic crystal structures. Using a pulse propagation technique that eliminates the interference from the boundary of finite photonic crystal structures, we show that the self-collimation phenomena can occur within a relatively wide bandwidth. We also demonstrate near-perfect operation efficiencies over wide frequency ranges in bends and splitters constructed by simply truncating the photonic crystal.
Experimental verification of backward-wave phenomenon by observation of reflection at angles larger than 90° in an anisotropic medium
Authors: Jen Yi-Jun
Published: October 2003

Calcite with its principal axes coordinates at an angle of φ=45° from its surface normal is used here to observe the anomalous reflection at the calcite/air interface. Light is incident from the lateral side of the crystal to yield an angle of reflection larger than 90°. The reflected backward wave behavior is detected by observing the direction in which the light exits the crystal. Reflectance is calculated according to the nonsymmetric reflection theory.
Distribution of spermatozoa in the outer perivitelline layer from above the germinal disc of emu and ostrich eggs
Authors: Malecki Irek A. , Martin Graeme B.
Published: October 2003

In the present study, we determined the distribution of spermatozoa in the perivitelline layer above the germinal disc (GD) of emu and ostrich eggs that had been laid at random intervals after mating. Eggs were opened, the perivitelline layer overlying the GD region was collected and sperm were visualized with 4′,6′-diamidino-2-phenylindole under a fluorescence microscope. To map the distribution of sperm, the GD was divided into six areas (A–F), with A being the centre of the GD and F the area furthest from the centre. In both species, more spermatozoa were found in areas B, C and D than in areas A, E and F. More than half the GD spermatozoa were found in areas B, C and D. The pattern of distribution of spermatozoa across the GD depended on the total number of sperm in the GD. In the emu, the pattern was related to delay since last copulation and time of laying, whereas in the ostrich the pattern was related to the month of the season and the sex ratio of the mating system. When the total number of spermatozoa in the GD increased, the number of spermatozoa increased in every area of the GD, but the centre and the outer areas were the least affected. We conclude that sperm numbers are highest in a band immediately around the centre of the GD and then decline with increasing distance from the centre. The low numbers in the centre of the GD may be due to either low attractiveness of the centre for sperm or high attractiveness of the area immediately adjacent to the centre.
Consequences of exposure to serum, with or without vitamin E supplementation, in terms of the fatty acid content and viability of bovine blastocysts produced in vitro
Authors: Reis A. , Rooke J. A. , McCallum G. J. , Staines M. E. , Ewen M. , Lomax M. A. , McEvoy T. G.
Published: October 2003

To determine whether serum supplementation influenced fatty acid content of bovine blastocysts and whether vitamin E addition to culture medium containing serum could improve development in vitro, cleaved eggs were cultured in synthetic oviduct fluid supplemented with bovine serum albumin (BSA, 0.4% w/v, fraction V) (SVBSA), fetal calf serum (FCS, 10% v/v) (SFCS) or FCS (10% v/v) plus 100 μM vitamin E (SFCS + E). Blastocyst yields were recorded and fatty acid composition was determined by gas chromatography. Day 7 blastocysts were incubated with [2-14C] pyruvate for 3 h and then fixed for cell counts. Yields of good quality blastocysts were greatest from cleaved eggs cultured in serum-free conditions (P < 0.01). In the presence of serum, supplementation with vitamin E increased both total and good quality blastocyst yields (P < 0.01). Presence of serum increased fatty acid content (mean ± SEM) of blastocysts (SVBSA v. SFCS = 57 ± 2  v. 74 ± 2 ng embryo−1; P < 0.001). In contrast, pyruvate metabolism was greater in blastocysts produced without serum (27 ± 3 v. 21 ± 3 picomoles embryo−13 h−1; P < 0.01) but, on a per cell basis, no differences were detected. Addition of vitamin E to the serum-supplemented formulation did not alter either the fatty acid content (73 ± 2 ng embryo−1) or pyruvate metabolism index (19 ± 1 pmol embryo−13 h−1) of SFCS + E blastocysts. Thus, despite lipid accumulation, supplementary vitamin E improved blastocyst yields in embryos exposed to serum.
Alkaline phosphatase activity in bovine oocytes and preimplantation embryos as affected by removal of the zona pellucida and culture medium constituents
Authors: Edwards J. L. , Powell A. M. , Rexroad Jr C. E.
Published: October 2003

The aims of the present study were: (1) to characterize alkaline phosphatase (AP) activity in bovine oocytes and embryos with intact or removed zona pellucida (ZP); and (2) to evaluate the effect of culture medium constituents on AP activity. Alkaline phosphatase activity in non-matured and matured oocytes was most evident nearest the plasma membrane and perivitelline space. In more than 90% of two- to 16-cell embryos, AP activity was observed in the perivitelline space and at blastomere contacts. In blastocysts, AP activity was localized to the trophectoderm. Only after immunodissection was AP activity detected in the inner cell mass. Removal of the ZP by pronase or mechanical means reduced AP activity. Alkaline phosphatase activity was detected in evacuated ZP after mechanical removal. Specific constituents comprising the embryo culture medium altered AP activity. Alkaline phosphatase activity was reduced in eight- to 16-cell embryos and evacuated ZP cultured in CR1aa + 0.4% bovine serum albumin compared with embryos cultured in CR1aa alone or embryos co-cultured on a monolayer of Buffalo rat liver cells in the presence of 10% fetal bovine serum. The presence of AP activity at blastomere contacts and in evacuated ZP limits its usefulness as a marker for the differentiation of embryonic cells comprising the early cleavage-stage embryo.
In vitro maturation of oocytes from non-stimulated common wombats
Authors: Cleary M. , West M. , Shaw J. , Jenkin G. , Trounson A.
Published: October 2003

Assisted reproductive techniques, such as in vitro oocyte maturation in conjunction with in vitro fertilisation, may be used as a tool to manipulate reproduction. Using the common wombat as a model for the critically endangered northern hairy-nosed wombat, the present study examined whether oocyte maturation could be achieved under field conditions. At the time of collection, no oocytes were at the metaphase II (MII) stage (0/42). After 60 h culture using the submarine incubation system, 34% of oocytes (24/70) matured to telophase/MII, as indicated by the presence of a polar body. The proportion of oocytes that reached MII was higher for oocytes collected from follicles >2 mm in diameter compared with follicles <2 mm (40% v. 22%, respectively). The presence of cumulus cells alone did not influence the maturation potential. Oocytes without cumulus cells collected from follicles >2 mm in diameter had the highest maturation rate (58%). Maturation was not affected by the reproductive status of the common wombat or a delay of up to 5 h before oocyte collection. In conclusion, the present study demonstrated that oocytes collected from non-stimulated common wombats can mature to MII in culture.
The two-by-two spectral Nevanlinna-Pick problem
Authors: Agler Jim , Young N.
Published: October 2003

We give a criterion for the existence of an analytic

2
×
2

2 \times 2

matrix-valued function on the disc satisfying a finite set of interpolation conditions and having spectral radius bounded by

1
1

. We also give a realization theorem for analytic functions from the disc to the symmetrised bidisc.
Examples of pleating varieties for twice punctured tori
Authors: Díaz Raquel , Series Caroline
Published: October 2003

We give an explicit description of some pleating varieties (sets with a fixed set of bending lines in the convex hull boundary) in the quasi-Fuchsian space of the twice punctured torus. In accordance with a conjecture of the second author, we show that their closures intersect Fuchsian space in the simplices of minima introduced by Kerckhoff. All computations are done using complex Fenchel-Nielsen coordinates for quasi-Fuchsian space referred to a maximal system of curves.
Variational principles for circle patterns and Koebe’s theorem
Authors: Bobenko Alexander , Springborn Boris
Published: October 2003

We prove existence and uniqueness results for patterns of circles with prescribed intersection angles on constant curvature surfaces. Our method is based on two new functionals—one for the Euclidean and one for the hyperbolic case. We show how Colin de Verdière’s, Brägger’s and Rivin’s functionals can be derived from ours.
Deriving calculus with cotriples
Authors: Johnson B. , McCarthy R.
Published: October 2003

We construct a Taylor tower for functors from pointed categories to abelian categories via cotriples associated to cross effect functors. The tower was inspired by Goodwillie’s Taylor tower for functors of spaces, and is related to Dold and Puppe’s stable derived functors and Mac Lane’s

Q
Q

-construction. We study the layers,

D

n

F
=
fiber
⁡
(

P

n

F
→

P

n
−
1

F
)

D_{n}F = \operatorname {fiber}(P_{n}F\rightarrow P_{n-1}F)

, and the limit of the tower. For the latter we determine a condition on the cross effects that guarantees convergence. We define differentials for functors, and establish chain and product rules for them. We conclude by studying exponential functors in this setting and describing their Taylor towers.
Symmetries of flat rank two distributions and sub-Riemannian structures
Authors: Sachkov Yuri
Published: October 2003

Flat sub-Riemannian structures are local approximations — nilpotentizations — of sub-Riemannian structures at regular points. Lie algebras of symmetries of flat maximal growth distributions and sub-Riemannian structures of rank two are computed in dimensions 3, 4, and 5.
Simple birational extensions of the polynomial algebra ℂ^{[3]}
Authors: Kaliman Shulim , Vénéreau Stéphane , Zaidenberg Mikhail
Published: October 2003

The Abhyankar-Sathaye Problem asks whether any biregular embedding

φ
:

C

k

↪

C

n

\varphi :\mathbb {C}^k\hookrightarrow \mathbb {C}^n

can be rectified, that is, whether there exists an automorphism

α
∈
Aut
⁡

C

n

\alpha \in \operatorname {Aut} \mathbb {C}^n

such that

α
∘
φ

\alpha \circ \varphi

is a linear embedding. Here we study this problem for the embeddings

φ
:

C

3

↪

C

4

\varphi :\mathbb {C}^3\hookrightarrow \mathbb {C}^4

whose image

X
=
φ
(

C

3

)

X=\varphi (\mathbb {C}^3)

is given in

C

4

\mathbb {C}^4

by an equation

p
=
f
(
x
,
y
)
u
+
g
(
x
,
y
,
z
)
=
0

p=f(x,y)u+g(x,y,z)=0

, where

f
∈

C

[
x
,
y
]
∖
{
0
}

f\in \mathbb {C}[x,y]\backslash \{0\}

and

g
∈

C

[
x
,
y
,
z
]

g\in \mathbb {C}[x,y,z]

. Under certain additional assumptions we show that, indeed, the polynomial

p
p

is a variable of the polynomial ring

C

[
4
]

=

C

[
x
,
y
,
z
,
u
]

\mathbb {C}^{[4]}=\mathbb {C}[x,y,z,u]

(i.e., a coordinate of a polynomial automorphism of

C

4

\mathbb {C}^4

). This is an analog of a theorem due to Sathaye (1976) which concerns the case of embeddings

C

2

↪

C

3

\mathbb {C}^2\hookrightarrow \mathbb {C}^3

. Besides, we generalize a theorem of Miyanishi (1984) giving, for a polynomial

p
p

as above, a criterion for when

X
=

p

−
1

(
0
)
≃

C

3

X=p^{-1}(0)\simeq \mathbb {C}^3

.
Chern numbers of ample vector bundles on toric surfaces
Authors: Di Rocco Sandra , Sommese Andrew
Published: October 2003

This article shows a number of strong inequalities that hold for the Chern numbers

c
1
2

c_1^2

,

c
2

c_2

of any ample vector bundle

E

\mathcal {E}

of rank

r
r

on a smooth toric projective surface,

S
S

, whose topological Euler characteristic is

e
(
S
)

e(S)

. One general lower bound for

c
1
2

c_1^2

proven in this article has leading term

(
4
r
+
2
)
e
(
S
)

ln
2

⁡

(

e
(
S
)

12

)

(4r+2)e(S)\ln _2\left (\tfrac {e(S)}{12}\right )

. Using Bogomolov instability, strong lower bounds for

c
2

c_2

are also given. Using the new inequalities, the exceptions to the lower bounds

c
1
2

>
4
e
(
S
)

c_1^2> 4e(S)

and

c
2

>
e
(
S
)

c_2>e(S)

are classified.
A version of Gordon’s theorem for multi-dimensional Schrödinger operators
Authors: Damanik David
Published: October 2003

We consider discrete Schrödinger operators

H
=
Δ
+
V

H = \Delta + V

in

ℓ
2

(

Z

d

)

\ell ^2(\mathbb {Z}^d)

with

d
≥
1

d \ge 1

, and study the eigenvalue problem for these operators. It is shown that the point spectrum is empty if the potential

V
V

is sufficiently well approximated by periodic potentials. This criterion is applied to quasiperiodic

V
V

and to so-called Fibonacci-type superlattices.
Introduction to the Special Issue
Authors: Aldrich John , Alt James
Published: October 2003

This special issue is devoted to original articles that reflect recent progress in one of the most exciting developments in Political Science, the National Science Foundation's (NSF) initiative called Empirical Implications of Theoretical Models (EITM). This initiative reflects the ideas and hard work of the Political Science team there, Jim Granato and Frank Scioli, backed up by the contributions of an EITM panel that assembled at NSF in July 2001, some of whose observations we mention below. The challenge set by the EITM program is straightforward: to improve our theoretical work so that it yields more testable hypotheses and to improve our methodological work so that testing is made more effective and informative about theories. It is hard to object to this, but it also turns out to be hard to meet fully. The EITM initiative contains several components designed to close the gap between theoretical derivation and empirical test. This issue represents one component, presenting some of the most innovative work in the discipline on the current research frontier in EITM.
Structure and Uncertainty in Discrete Choice Models
Authors: Signorino Curtis S.
Published: October 2003

Social scientists are often confronted with theories in which one or more actors make choices over a discrete set of options. In this article, I generalize a broad class of statistical discrete choice models, with both well-known and new nonstrategic and strategic special cases. I demonstrate how to derive statistical models from theoretical discrete choice models and, in doing so, I address the statistical implications of three sources of uncertainty: agent error, private information about payoffs, and regressor error. For strategic and some nonstrategic choice models, the three types of uncertainty produce different statistical models. In these cases, misspecifying the type of uncertainty leads to biased and inconsistent estimates, and to incorrect inferences based on estimated probabilities.
Roll Calls, Party Labels, and Elections
Authors: Snyder James M. , Ting Michael M.
Published: October 2003

We develop a model of legislative policymaking in which individual legislators are concerned with both policy and reelection. Legislators' preferences are private information, and they have two means of communicating their preferences to voters. First, they each have a “party label” that credibly identifies an interval within which their ideal points must lie. Second, their roll call votes may convey additional information about their preferences. Each legislator must therefore tailor his or her votes to his or her district in order to forestall a reelection challenge from the opposing party. In equilibrium, nonsincere voting records will occur mostly in moderate districts, where extreme incumbents are vulnerable to challenges from relatively centrist candidates. In those districts, the most extreme legislators may even choose to vote sincerely and retire rather than compile a moderate voting record. Thus, both roll call scores and candidate types will be responsive to district type. An empirical test of shifts in roll call scores of retiring House members in moderate districts confirms these findings.
Alaska Native Mortality, 1979–1998
Authors: Day Gretchen Ehrsam , Lanier Anne P.
Published: October 2003

Objectives.

This study compares mortality patterns for the Alaska Native population and the U.S. white population for 1989–1998 and examines trends for the 20-year period 1979–1998.

Methods.

The authors used death certificate data and Indian Health Service population estimates to calculate mortality rates for the Alaska Native population, age-adjusted to the U.S. 1940 standard million. Data on population and mortality for U.S. whites, aggregated by 10-year age groups and by gender, were obtained from the National Center for Health Statistics, and U.S. white mortality rates were age-adjusted to the U.S. 1940 standard million.

Results.

Overall, 1989–1998 Alaska Native mortality rates were 60% higher than those for the U.S. white population for the same period. There were significant disparities for eight of 10 leading causes of death, particularly unintentional injury, suicide, and homicide/legal intervention. Although declines in injury rates can be documented for the period 1979–1998, large disparities still exist. Alaska Native death rates for cancer, cerebrovascular disease, chronic obstructive pulmonary disease, and diabetes increased from 1979 to 1998. Given decreases in some cause-specific mortality rates in the U.S. white population, increased rates among Alaska Natives have resulted in new disparities.

Conclusions.

These data indicate that improvements in injury mortality rates are offset by marked increases in chronic disease deaths.
Couples treatment for major depression: critique of the literature and suggestions for some different directions
Authors: Gupta Maya , Coyne James C. , Beach Steven R. H.
Published: October 2003

Current couples approaches to the treatment of depression show considerable promise for some couples, but have substantial room for improvement – in terms of efficacy as well as applicability and acceptability to a broader population. Although conjoint approaches have been shown to be efficacious in reducing couple distress and are possibly efficacious in ameliorating depression that co‐occurs with couple distress, methodological problems hamper generalization from the published findings. Therefore, it is not clear that most depressed persons are likely to benefit from currently available conjoint formats. Most basically, there may often be obstacles that prevent or delay partner involvement, highlighting the need for treatments that can enhance relationship functioning without relying on a conjoint format. Existing treatment delivery systems may also fail to reach a considerable segment of the population. Developing a more flexible set of options for implementing couple‐focused treatment, as well as rethinking dominant assumptions about depression, may be integral to extending the viability of couples therapy for depression.
The ongoing silencing of women in families: an analysis and rethinking of premenstrual syndrome and therapy
Authors: Ussher Jane M.
Published: October 2003

Traditionally, explanations for premenstrual symptomatology have focused on the individual woman as the site of difficulties, and as the sole target of intervention. In contrast, from the perspective of a material‐discursive‐intrapsychic model, this paper will focus on the ways in which ‘PMS’ is experienced, constructed and dealt with in family relationships. Drawing on in‐depth narrative interviews conducted with women with moderate to severe premenstrual symptoms, it is argued that ‘PMS’ is closely tied to relationship difficulties and responsibilities; familial expectations and attributions for women's behaviour provide a discursive context for behaviour and emotions to be positioned as ‘PMS’; and that the ongoing self‐silencing and pathologization of women's emotions in families are key attributes of ‘PMS’. This suggests that a consideration of relationship issues should be central to any assessment or intervention for premenstrual symptoms, and conversely, that attention should be given to premenstrual exacerbation of relationship difficulties in family or couples therapy.
Outcome studies of family therapy in child and adolescent depression
Authors: Cottrell David
Published: October 2003

There is surprisingly little good‐quality evidence for the effectiveness of family systemic interventions with child and adolescent depression given the prevalence of depression and the demonstrated association with a range of family factors. What studies there are suggest the possibility of family therapy being an effective intervention but more research is needed before firm conclusions may be drawn. Family interventions may be more effective in children than in adolescents and where other family members are depressed. It is possible that family interventions continue to bring about improvement in symptoms after cessation of treatment. What research there is evaluates older structural models of therapy: there is a real need for more evaluation of newer models of practice.
The family therapy journals in 2002: a thematic review
Authors: Rivett Mark
Published: October 2003

This article reviews the principal English‐language (including British) family therapy journals for the year 2002. A number of common themes and threads predominate within these journals. Articles relating to these themes are reported under distinct headings. These themes were: responding to 9/11; marital therapy and diversity practice. Significant research papers are incorporated into the relevant heading. This is the final thematic review undertaken by the current author.
Slotting Allowances as a Facilitating Practice by Food Processors in Wholesale Grocery Markets: Profitability and Welfare Effects
Authors: Hamilton Stephen F.
Published: October 2003

Slotting allowances, which are lump‐sum transfers paid by food manufacturers to grocery retailers in return for various retail concessions, are becoming increasingly common in wholesale grocery markets. This article extends the literature on slotting allowances by considering two features that previously have been ignored: the role of food processors in determining these pricing arrangements, and the effect of slotting allowances on the size and distribution of economic surplus. Slotting allowances motivated by food processors increase procurement quantities and farm prices, and this raises farm surplus, increases total producer surplus, and improves consumer welfare in the food system.
Shared Agents and Competition in Laboratory English Auctions
Authors: Menkhaus Dale J. , Phillips Owen R. , Coatney Kalyn T.
Published: October 2003

At livestock auctions, the same purchasing agent can represent more than one processor. Repeated multiple‐unit English auctions are created in a laboratory to measure the impact of shared agents on trade prices under alternative treatments with six, and as few as two, agents representing six principals. Treatments are constructed in which the agents either know or do not know quantity for sale, and in which there are progressively fewer agents bidding. Knowledge of quantity for sale can be anticompetitive. Evolution toward increased market concentration leads to consistent anticompetitive pricing, resulting in prices significantly lower than the predicted competitive equilibrium prices.
Effects of Cheap Talk on Consumer Willingness‐to‐Pay for Golden Rice
Authors: Lusk Jayson L.
Published: October 2003

A large body of literature suggests willingness‐to‐pay is overstated in hypothetical valuation questions as compared to when actual payment is required. Recently, “cheap talk” has been proposed to eliminate the potential bias in hypothetical valuation questions. Cheap talk refers to process of explaining hypothetical bias to individuals prior to asking a valuation question. This study explores the effect of cheap talk in a mass mail survey using a conventional value elicitation technique. Results indicate that cheap talk was effective at reducing willingness‐to‐pay for most survey participants; however, consistent with previous research, cheap talk did not reduce willingness‐to‐pay for knowledgeable consumers.
Spatial and Temporal Marketing Considerations under Marketing Loan Programs
Authors: Saak Alexander E.
Published: October 2003

Marketing assistance loan (MAL) and loan deficiency payment (LDP) programs differ in their treatment of transportation costs. Marketing decisions are analyzed under these programs when producers are differentiated by location with respect to the terminal market. Under certain conditions, a complete characterization of equilibrium is developed. The proposed model broadly fits several “stylized” facts about producer enrollment in these programs. If LDPs are uniform at all locations, LDP programs do not interfere with marketing decisions. MAL programs distort the optimal marketing pattern by providing incentives to store for producers who should be among the first ones to supply the market.
Impacts of Declining U.S. Retail Beef Demand on Farm‐Level Beef Prices and Production
Authors: Marsh John M.
Published: October 2003

A systems model was estimated to determine the effects of declining U.S. retail beef demand on farm‐level beef prices and production. Retail beef demand declined by nearly 66% from 1976 to 1999. Results indicate autonomous shifts in retail demand significantly impacted farm‐level demands and production. Based on equilibrium multipliers, the 1976–99 reduction in beef demand decreased real slaughter cattle prices and production by 32.1% and 11.2%, respectively. Real feeder cattle prices and production decreased by 8.0% and 22.6%, respectively. Combining the decreases in farm prices and production, slaughter and feeder cattle producers experienced a real revenue reduction of $13.3 billion (61%) due to the long‐term decline in demand.
Bridging the Gap between Partial and Total Factor Productivity Measures Using Directional Distance Functions
Authors: Nin Alejandro , Arndt Channing , Hertel Thomas W. , Preckel Paul V.
Published: October 2003

Technical dependencies as well as data constraints limit our ability to allocate inputs across sectors and hence our ability to measure sectoral productivity. We adapt a directional measure of efficiency to the measurement of sector‐specific productivity that does not require allocating all inputs across sectors. Applied to the agricultural sector of a group of countries, the results show important differences in livestock and crops productivity growth. Commonly used partial factor productivity measures for livestock and crops tend to overestimate productivity growth in most developing countries while underestimating it in European countries.
Efficiency and Technical Change in the Philippine Rice Sector: A Malmquist Total Factor Productivity Analysis
Authors: Umetsu Chieko , Lekprichakul Thamana , Chakravorty Ujjayant
Published: October 2003

Regional differences in total factor productivity, efficiency, and technological change in the Philippine rice sector are examined for the post‐Green Revolution era. Malmquist productivity indices were constructed for 1971–90 and were decomposed into efficiency and technological change. The average annual Malmquist productivity growth was only slightly positive. Productivity growth was negative during the early 1970s, and was followed by a period of positive growth. Growth was negative again in the late 1980s. The period of positive growth coincided with the introduction of new rice varieties while the declines are likely to have been caused by intensification of rice production in lowland farming systems. Certain regions such as Central Luzon, Western Visayas, and Southern and Northern Mindanao had higher rates of technological change than others. This may be due to higher investments in infrastructure and education, increased adoption of tractors, and a better agroclimatic environment.
Protectionism, Trade, and Measures of Damage from Exotic Species Introductions
Authors: Costello Christopher , McAusland Carol
Published: October 2003

Unintentional introductions of nonindigenous plants, animals, and microbes cause significant ecological and agricultural crop damage worldwide. Trade in both manufactured and agricultural goods is a primary vector for such introductions. Fusing simple models of trade and biological introductions, we explore the links between trade, protectionism, and damage arising from exotic species introductions. We show that it is possible for freer trade to reduce damage arising from exotic species invasions. We also show how current measures of damage—heavily weighted toward agricultural damage—serve as misleading indicators of how restrictions to trade affect total losses arising from exotic species introductions.
A Joint Framework for Analysis of Agri‐Environmental Payment Programs
Authors: Cooper Joseph C.
Published: October 2003

This article presents an approach for simultaneously estimating farmers' decisions to accept incentive payments in return for adopting a bundle of environmentally benign best management practices. Using the results of a multinomial probit analysis of surveys of over 1,000 farmers facing five adoption decisions in a voluntary program, we show how the farmers' perceptions of the desirability of various bundles change with the offer amounts and with which practices are offered in the bundle. We also demonstrate an estimator for the mean minimum willingness to accept for the adoption of a practice conditional on the cost share offers for other practices.
Measuring Interactions among Urbanization, Land Use Regulations, and Public Finance
Authors: Cho Seong‐Hoon , Wu JunJie , Boggess William G.
Published: October 2003

This article presents a polychotomous choice‐selectivity model to estimate the interactions among urbanization, land use regulations, and public finance in five western states (California, Idaho, Nevada, Oregon, and Washington). Land use regulations in these five states reduced the total developed area by an estimated 12.2% from 1982 to 1992, but increased housing prices between 1.3% and 4.7%, depending on the intensity of land use regulations in a county. Land use regulations also reduced public expenditure and property tax in the long run by 5.6% and 8.4%, respectively, but increased public expenditure and property tax in the short run by 9.8% and 12.6%.
Rural Amenity Values and Length of Residency
Authors: Johnston Robert J. , Swallow Stephen K. , Tyrrell Timothy J. , Bauer Dana Marie
Published: October 2003

New residents of rural communities are often assumed to have preferences for development and conservation that differ from those of longer‐term residents. However, the literature offers little to quantify presumed preference heterogeneity. This article assesses whether stated preferences differ according to length of residency. Results are based on a conjoint (choice experiment) survey of Rhode Island rural residents. Heterogeneity—according to length of town residency—is modeled using dummy variables, multiplicative interactions, and Lagrangian interpolation polynomials. Results are compared across the three models, and identify a range of attributes for which willingness to pay depends on length of residency.
Determinants of Land Use in Amazônia: A Fine‐Scale Spatial Analysis
Authors: Chomitz Kenneth M. , Thomas Timothy S.
Published: October 2003

Wetter areas of the Amazon basin exhibit lower rates of agricultural conversion. Previous analyses, using relatively aggregate data on land cover, have been unable to determine the extent to which this reflects limited access versus unfavorable agroclimatic conditions. This article uses census‐tract level data for the Brazilian Amazon to relate forest conversion and pasture productivity to precipitation, soil quality, infrastructure and market access, proximity to past conversion, and protection status. The probability that land is used for agriculture or intensively stocked with cattle declines markedly with increasing rainfall, other things equal.
Efficient Estimation of Agricultural Time Series Models with Nonnormal Dependent Variables
Authors: Ramírez Octavio A. , Misra Sukant K. , Nelson Jeannie
Published: October 2003

This article proposes using an expanded form of the Johnson SU family as a way to approximate nonnormal distributions in regression models. The distribution is one of the few that allows modeling heteroskedasticity and autocorrelation. The technique is evaluated with Monte Carlo simulation and illustrated through an empirical model of the West Texas cotton basis. Given nonnormality, this technique can substantially reduce the variance of slope parameter estimates relative to least squares procedures.
Spatial Market Arbitrage and Threshold Cointegration
Authors: Sephton Peter S.
Published: October 2003

Goodwin and Piggott reported that corn and soybean prices in spatially separated markets in North Carolina exhibited threshold cointegration and that commodity prices in different markets may persistently diverge. Here, a multivariate approach is used to test for threshold cointegration and nonlinear cointegration. The results suggest that departures from the law of one price do not persist indefinitely.
The Political Dynamics of Sub-State Regionalisation: A Neo-Functionalist Perspective and the Case of Devolution in the UK
Authors: Bradbury Jonathan
Published: October 2003

The article seeks to contribute to theoretical analysis of sub-state regionalisation, particularly as applied to the study of its principal history-making developments. It argues that cross-fertilising the classic neo-functionalist perspective on European supranational regionalisation offers a profitable basis for development. The article clarifies its conceptual categories, adapting to take account of the sub-state context, and then applies the approach to devolution in the UK. Reference to this case seeks to confirm the utility of the perspective, and in the process offers a novel framework for clarifying the common and distinctive political dynamics of devolution across the UK.
The dynamics of technology strategy: an exploratory study
Authors: Davenport Sally , Campbell‐Hunt Colin , Solomon Julia
Published: October 2003

A study of the evolution of competitive capabilities in exemplar New Zealand firms identified that technology strategy played the key role in motivating the firms' transition to positions of global prominence. Adequate description of these transitions required a view of technology strategy that is more dynamic than those typically available. We use complexity theory to identify, first, a number of positive feedback loops that have driven the technological progression of these firms, second to identify the complex webs of strategic development within which technology has progressed, and finally to explain why these trajectories carry firms to positions of distinctive advantage. These loops come together to impel firms through a radical transition from broad technology dabblers to focussed technology specialists. We view the study as exploratory to a class of studies aimed at understanding the evolution of technology strategy over time.