bluuebunny/crossref_metadata_2025 huggingface dataset:
empty spiraclesis required for the development of olfactory projection neuron circuitry inDrosophila
Authors: Lichtneckert Robert , Nobs Lionel , Reichert Heinrich
Published: June 2008

In both insects and mammals, second-order olfactory neurons receive input from olfactory receptor neurons and relay olfactory input to higher brain centers. In Drosophila, the wiring specificity of these olfactory projection neurons (PNs) is predetermined by their lineage identity and birth order. However, the genetic programs that control this wiring specificity are not well understood. The cephalic gap gene empty spiracles(ems) encodes a homeodomain transcription factor required for embryonic development of the antennal brain neuromere. Here we show that ems is expressed postembryonically in the progenitors of the two major olfactory PN lineages. Moreover, we show that ems has cell lineage-specific functions in postembryonic PN development. Thus, in the lateral PN lineage, transient ems expression is essential for development of the correct number of PNs; in ems mutants, the number of PNs in the lineage is dramatically reduced by apoptosis. By contrast, in the anterodorsal PN lineage, transient ems expression is necessary for precise targeting of PN dendrites to appropriate glomeruli; in ems mutants, these PNs fail to innervate correct glomeruli, innervate inappropriate glomeruli, or mistarget dendrites to other brain regions. Furthermore, in the anterodorsal PN lineage, ems controls the expression of the POU-domain transcription factor Acj6 in approximately half of the cells and, in at least one glomerulus, ems function in dendritic targeting is mediated through Acj6. The finding that Drosophila ems, like its murine homologs Emx1/2, is required for the formation of olfactory circuitry implies that conserved genetic programs control olfactory system development in insects and mammals.
Placental rescue reveals a sole requirement for c-Myc in embryonic erythroblast survival and hematopoietic stem cell function
Authors: Dubois Nicole C. , Adolphe Christelle , Ehninger Armin , Wang Rong A. , Robertson Elisabeth J. , Trumpp Andreas
Published: June 2008

The c-Myc protein has been implicated in playing a pivotal role in regulating the expression of a large number of genes involved in many aspects of cellular function. Consistent with this view, embryos lacking the c-myc gene exhibit severe developmental defects and die before midgestation. Here, we show that Sox2Cre-mediated deletion of the conditional c-mycflox allele specifically in the epiblast (hence trophoectoderm and primitive endoderm structures are wild type) rescues the majority of developmental abnormalities previously characterized in c-myc knockout embryos, indicating that they are secondary defects and arise as a result of placental insufficiency. Epiblast-restricted c-Myc-null embryos appear morphologically normal and do not exhibit any obvious proliferation defects. Nonetheless, these embryos are severely anemic and die before E12. c-Myc-deficient embryos exhibit fetal liver hypoplasia,apoptosis of erythrocyte precursors and functionally defective definitive hematopoietic stem/progenitor cells. Specific deletion of c-mycflox in hemogenic or hepatocytic lineages validate the hematopoietic-specific requirement of c-Myc in the embryo proper and provide in vivo evidence to support a synergism between hematopoietic and liver development. Our results reveal for the first time that physiological levels of c-Myc are essential for cell survival and demonstrate that, in contrast to most other embryonic lineages, erythroblasts and hematopoietic stem/progenitor cells are particularly dependent on c-Myc function.
The Frank–Starling mechanism in vertebrate cardiac myocytes
Authors: Shiels Holly A. , White Ed
Published: June 2008

The Frank–Starling law of the heart applies to all classes of vertebrates. It describes how stretch of cardiac muscle, up to an optimum length, increases contractility thereby linking cardiac ejection to cardiac filling. The cellular mechanisms underlying the Frank–Starling response include an increase in myofilament sensitivity for Ca2+, decreased myofilament lattice spacing and increased thin filament cooperativity. Stretching of mammalian, amphibian and fish cardiac myocytes reveal that the functional peak of the sarcomere length (SL)–tension relationship occurs at longer SL in the non-mammalian classes. These findings correlate with in vivo cardiac function as non-mammalian vertebrates, such as fish,vary stroke volume to a relatively larger extent than mammals. Thus, it seems the length-dependent properties of individual myocytes are modified to accommodate differences in organ function, and the high extensibility of certain hearts is matched by the extensibility of their myocytes. Reasons for the differences between classes are still to be elucidated, however, the structure of mammalian ventricular myocytes, with larger widths and higher levels of passive stiffness than those from other vertebrate classes may be implicated.
The free-flight response ofDrosophilato motion of the visual environment
Authors: Mronz Markus , Lehmann Fritz-Olaf
Published: June 2008

In the present study we investigated the behavioural strategies with which freely flying fruit flies (Drosophila) control their flight trajectories during active optomotor stimulation in a free-flight arena. We measured forward, turning and climbing velocities of single flies using high-speed video analysis and estimated the output of a`Hassenstein–Reichardt' elementary motion detector (EMD) array and the fly's gaze to evaluate flight behaviour in response to a rotating visual panorama. In a stationary visual environment, flight is characterized by flight saccades during which the animals turn on average 120° within 130 ms. In a rotating environment, the fly's behaviour typically changes towards distinct, concentric circular flight paths where the radius of the paths increases with increasing arena velocity. The EMD simulation suggests that this behaviour is driven by a rotation-sensitive EMD detector system that minimizes retinal slip on each compound eye, whereas an expansion-sensitive EMD system with a laterally centred visual focus potentially helps to achieve centring response on the circular flight path. We developed a numerical model based on force balance between horizontal, vertical and lateral forces that allows predictions of flight path curvature at a given locomotor capacity of the fly. The model suggests that turning flight in Drosophila is constrained by the production of centripetal forces needed to avoid side-slip movements. At maximum horizontal velocity this force may account for up to 70%of the fly's body weight during yaw turning. Altogether, our analyses are widely consistent with previous studies on Drosophila free flight and those on the optomotor response under tethered flight conditions.
Oxygen consumption by a coral reef sponge
Authors: Hadas Eran , Ilan Micha , Shpigel Muki
Published: June 2008

Oxygen consumption of the Red Sea coral reef sponge Negombata magnifica was measured using both incubation and steady-state methods. The latter method was found to be the more reliable because sponge activity remained stable over time. Oxygen consumption rate was measured during three levels of sponge activity: full activity, reduced activity and basal activity(starved). It was found that the active oxygen consumption rate of N. magnifica averaged 37.3±4.6 nmol O2min–1 g–1 wet mass, which is within the upper range reported for other tropical marine sponges. Fully active N. magnifica individuals consumed an average of 41.8±3.2 nmol O2 min–1 g–1 wet mass. The mean basal respiration rate was 20.2±1.2 nmol O2min–1 g–1 wet mass, which is 51.6±2.5% of the active respiration rate. Therefore, the oxygen used for water pumping was calculated to be at most 10.6±1.8 nmol O2 min–1 g–1 wet mass, which is 25.1±3.6% of the total respiration. Combined oxygen used for maintenance and water pumping activity was calculated to be 30.8 nmol O2 min–1 g–1 wet mass, which is approximately 74% of the sponge's total oxygen requirement. The remaining oxygen is directed to other physiological activities, mainly the energy requirement of growth. These findings suggest that only a relatively minor amount of energy is potentially available for growth, and thus might be a factor in controlling the growth rate of N. magnifica in oligotrophic coral reefs.
Wing kinematics measurement and aerodynamics of hovering droneflies
Authors: Liu Yanpeng , Sun Mao
Published: June 2008

The time courses of wing and body kinematics of three freely hovering droneflies (Eristalis tenax) were measured using 3D high-speed video,and the morphological parameters of the wings and body of the insects were also measured. The measured wing kinematics was used in a Navier–Stokes solver to compute the aerodynamic forces and moments acting on the insects. The time courses of the geometrical angle of attack and the deviation angle of the wing are considerably different from that of fruit flies recently measured using the same approach. The angle of attack is approximately constant in the mid portions of a half-stroke (a downstroke or upstroke) and varies rapidly during the stroke reversal. The deviation angle is relatively small and is higher at the beginning and the end of a half-stroke and lower at the middle of the half-stroke, giving a shallow U-shaped wing-tip trajectory. For all three insects considered, the computed vertical force is approximately equal to the insect weight (the difference is less than 6% of the weight) and the computed horizontal force and pitching moment about the center of mass of the insect are approximately zero. The computed results satisfying the equilibrium flight conditions, especially the moment balance condition, validate the computation model. The lift principle is mainly used to produce the weight-supporting vertical force, unlike the fruit flies who use both lift and drag principles to generate the vertical force; the vertical force is mainly due to the delayed stall mechanism. The magnitude of the inertia power is larger than that of the aerodynamic power, and the largest possible effect of elastic storage amounts to a reduction of flight power by around 40%, much larger than in the case of the fruit fly.
Navigational abilities of homing pigeons deprived of olfactory or trigeminally mediated magnetic information when young
Authors: Gagliardo Anna , Ioalè Paolo , Savini Maria , Wild Martin
Published: June 2008

Anatomical evidence and conditioning experiments have recently suggested that magnetoreceptors are located in the upper beak of homing pigeons, where they are innervated by the ophthalmic branch of the trigeminal nerve. These findings have raised the issue of whether the trigeminally mediated magnetoreception is involved in the navigational mechanisms of homing pigeons. Recent data have shown that, in inexperienced pigeons, section of the ophthalmic branch of the trigeminal nerve does not impair navigational abilities, whereas the navigational performance of inexperienced pigeons is disrupted after section of the olfactory nerve. Nevertheless, the issue of whether the stimuli available during development of the navigational mechanism can influence the types of cues used in determining the direction of displacement remains unresolved. To address this issue, we surgically deprived young pigeons of either olfactory or trigeminally mediated magnetic information, and then later tested their navigational abilities subsequent to an intensive training flight program of up to 10 km in different directions. The birds deprived of trigeminally mediated magnetic information when young developed navigational abilities at the same level as intact control pigeons,whereas the olfactory deprived pigeons displayed randomly scattered initial orientation and poor homing performance. Our data show that olfactory cues are needed for the development of navigational abilities from unfamiliar locations and that the lack of magnetic information does not affect the development of homing abilities.
Modulation, individual variation and the role of lingual sensory afferents in the control of prey transport in the lizardPogona vitticeps
Authors: Schaerlaeken Vicky , Herrel Anthony , Meyers J. J.
Published: June 2008

Most organisms feed on a variety of food items that may differ dramatically in their physical and behavioural characteristics (e.g. mobility, mass,texture, etc.). Thus the ability to modulate prey transport behaviour in accordance with the characteristics of the food appears crucial. Consequently,prey reduction and transport movements must be adjusted to the natural variation in material properties of the food, between and within feeding sequences and transport cycles. Here we describe an investigation of (1) the ability of the agamid lizard Pogona vitticeps to modulate prey transport kinematics when feeding on a range of food items differing in their physical characteristics and (2) the role of sensory feedback in controlling jaw and tongue movements by bilateral transection of the lingual trigeminal sensory afferents. Our findings demonstrate that P. vitticepsmodulates the kinematics of its feeding behaviour in response to the mechanical demands imposed by different food types. In addition, transection of the trigeminal sensory afferents has an effect on the movements of jaws and tongue during transport, and increases the duration of transport cycles needed to process a given food type. However, after transection, transport cycles were still different for different food types suggesting that other sources of sensory information are also used to modulate prey transport in the lizard P. vitticeps.
Three- and four-element Windkessel models: Assessment of their fitting performance in a large cohort of healthy middle-aged individuals
Authors: Segers P , Rietzschel E R , De Buyzere M L , Stergiopulos N , Westerhof N , Van Bortel L M , Gillebert T , Verdonck P R
Published: June 2008

Lumped-parameter models are used to estimate the global arterial properties by fitting the model to measured (aortic) pressure and flow. Different model configurations coexist, and it is still an open question as to which model optimally reflects the arterial tree and leads to correct estimates of arterial properties. An assessment was made of the performance of (a) the three-element Windkessel model (WK3) consisting of vascular resistance R, total arterial compliance C, and characteristic impedance Zc; (b) a four-element model with an inertance element L placed in parallel with Zc (WK4-p); and (c) a four-element model with L placed in series with Zc (WK4-s). Models were fitted to data measured non-invasively in 2404 healthy subjects, aged between 35 and 55 years. It was found that model performance segregated into two groups. In a group containing 20 per cent of the dataset (characterized by low blood pressure and wave reflection) the WK4-p model outperformed the other models, with model behaviour as envisioned by its promoters. In these cases, the WK3 and WK4-s models led to increased overestimation of total arterial compliance and underestimation of characteristic impedance. However, in about 80 per cent of the cases, the WK4-p model showed a behaviour that was very similar to that of the WK3 and WK4-s models. Here, the WK4-s model yielded the best quality of fit, although model parameters reached physically impossible values for L in about 12 per cent of all cases. The debate about which lumped-parameter model is the better approximation of the arterial tree is therefore still not fully resolved.
Measurement and analysis of the flow field in a pulsatile ventricular assist device
Authors: Nugent A H , Bertram C D
Published: June 2008

A pneumatically driven ventricular assist device (VAD) of unconventional geometry, designed to mitigate adverse haemostatic phenomena by optimization of flow patterns, was investigated using two-component laser Doppler anemometry (LDA). Data were taken on a rectilinear grid over two orthogonal traverses, allowing synthesis of three-dimensional velocity vectors over most of the grid. The resulting data were examined by two-dimensional and three-dimensional static and animated computer graphic visualizations of the time-varying vector fields. This analysis revealed illuminating and previously unobserved features of the complex flow fields within pulsatile VADs and identified design considerations that bear upon minimization of turbulence and of flow recirculation and stasis. The findings of this study suggest that, while total abolition of undesirable flow phenomena in a diaphragm-type blood pump is probably impossible, comprehensive investigation in vitro can engender considerable improvements in the efficacy of a device.
Experimental and numerical modelling of the ventriculosinus shunt (El-Shafei shunt)
Authors: Van Canneyt K , Kips J , Mareels G , Baert E , Van Roost D , Verdonck P
Published: June 2008

This study assesses malresorptive hydrocephalus treatment by ventriculosinus shunting with the shunt in the antegrade or retrograde position. First, an experimental model of the cerebral ventricles, the arachnoid villi, the cortical veins, and the superior sagittal sinus was built. For this purpose, the compliance of a human cortical vein was measured and then modelled by means of Penrose tubes. The dimensions of the superior sagittal sinus were determined in vivo by measurements on magnetic resonance imaging scans of 21 patients. Second, a numerical model of the cortical veins and the superior sagittal sinus was built. The numerical results were validated with the results from the experimental model. The experimental and numerical pressure difference between the intracranial pressure and the static sinus pressure was small (0–20 Pa) and corresponded to the theoretically expected values. No overdrainage was found in either the antegrade or the retrograde position of the shunt. Blood reflow was only found while mimicking lumbar puncture or changes in position with the experimental model (lowering the intracranial pressure or increasing the sinus pressure rapidly). Optimal results can be obtained with the shunt positioned in the most downstream half of the superior sagittal sinus. The experimental and numerical results confirm the potential of ventriculosinus shunting as therapy for malresorptive hydrocephalus patients. The ventriculosinus shunt thus proves to be a promising technique.
A model morphology of the pulmonary acinus
Authors: Leeming A , Schroter R
Published: June 2008

A variation of a mathematical model of the structure of a pulmonary ventilatory unit is used to generate its internal ductal tree and associated alveolar architecture. The model unit comprises a space-filling block of regular polyhedra; ducts and alveoli were formed by opening specific common faces between polyhedra. The model employs a physically reasonable optimization strategy of maximizing gas exchange while minimizing the mean transit time to ventilate the ventilatory unit (assumed to be proportional to the mean path length) in order to create the ductal tree. The sensitivity of the global architecture to the competitive optimization parameters used and the tree structure are compared with independently published measurements. The study concludes that it is possible to model the detailed architecture of a unit using a simple space-invariant uniform modular structure for both alveoli and ductal parts. The close similarity between model and experimental measurement strongly suggests that the optimization used to create the unit is a likely one from a functional biological standpoint. The insensitivity of the architecture to the competition between the optimization parameters supports the belief that it is not important to consider the detailed measured size distribution of alveoli when considering how the large structure of the ventilatory unit is built up.
Measurement of pulsatile haemodynamic forces in a model of a bifurcated stent graft for abdominal aortic aneurysm repair
Authors: Zhou S N , How T V , Black R A , Vallabhaneni S R , McWilliams R , Brennan J A
Published: June 2008

The longitudinal haemodynamic force (LF) acting on a bifurcated stent graft for abdominal aortic aneurysm repair has been estimated previously using a simple one-dimensional analytical model based on the momentum equation which assumes steady flow of an inviscid fluid. Using an instrumented stent-graft model an experimental technique was developed to measure the LF under pulsatile flow conditions. The physical stent-graft model, with main trunk diameter of 30 mm and limb diameters of 12 mm, was fabricated from aluminium. Strain gauges were bonded on to the main trunk to determine the longitudinal strain which is related to the LF. After calibration, the model was placed in a pulsatile flow system with 40 per cent aqueous glycerol solution as the circulating fluid. The LF was determined using a Wheatstone bridge signal-conditioning circuit. The signals were averaged over 590 cardiac cycles and saved to a personal computer for subsequent processing. The LF was strongly dependent on the pressure but less so on the flowrate. The measured forces were higher than those predicted by the simplified mathematical model by about 6–18 per cent during the cardiac cycle. The excess measured forces are due to the viscous drag and the effect of pulsatile flow. The peak measured LF in this model of 30 mm diameter may exceed the fixation force of some current clinical endovascular stent grafts.
Separation of the reservoir and wave pressure and velocity from measurements at an arbitrary location in arteries
Authors: Aguado-Sierra J , Alastruey J , Wang J-J , Hadjiloizou N , Davies J , Parker K H
Published: June 2008

Previous studies based on measurements made in the ascending aorta have demonstrated that it can be useful to separate the arterial pressure P into a reservoir pressure P generated by the windkessel effect and a wave pressure p generated by the arterial waves: P= P + p. The separation in these studies was relatively straightforward since the flow into the arterial system was measured. In this study the idea is extended to measurements of pressure and velocity at sites distal to the aortic root where flow into the arterial system is not known. P is calculated from P at an arbitrary location in a large artery by fitting the pressure fall-off in diastole to an exponential function and assuming that p is proportional to the flow into the arterial system. A local reservoir velocity Ū that is proportional to P is also defined. The separation algorithm is applied to in vivo human and canine data and to numerical data generated using a one-dimensional model of pulse wave propagation in the larger conduit arteries. The results show that the proposed algorithm is reasonably robust, allowing for the separation of the measured pressure and velocity into reservoir and wave pressures and velocities. Application to data measured simultaneously in the aorta of the dog shows that the reservoir pressure is fairly uniform along the aorta, a test of self-consistency of the assumptions leading to the algorithm. Application to data generated with a validated numerical model indicates that the parameters derived by fitting the pressure data are close to the known values which were used to generate the numerical data. Finally, application to data measured in the human thoracic aorta indicates the potential usefulness of the separation.
The compression and expansion waves of the forward and backward flows: An in-vitro arterial model
Authors: Feng J , Khir A W
Published: June 2008

Although the propagation of arterial waves of forward flows has been studied before, that of backward flows has not been thoroughly investigated. The aim of this research is to investigate the propagation of the compression and expansion waves of backward flows in terms of wave speed and dissipation, in flexible tubes. The aim is also to compare the propagation of these waves with those of forward flows.

A piston pump generated a flow waveform in the shape of approximately half-sinusoid, in flexible tubes (12 mm and 16 mm diameter). The pump produced flow in either the forward or the backward direction by moving the piston forward, in a ‘pushing action’ or backward, in a ‘pulling action’, using a graphite brushes d.c. motor. Pressure and flow were measured at intervals of 5 cm along each tube and wave speed was determined using the PU-loop method. The simultaneous measurements of diameter were also taken at the same position of the pressure and flow in the 16 mm tube. Wave intensity analysis was used to determine the magnitude of the pressure and velocity waveforms and wave intensity in the forward and backward directions.

Under the same initial experimental conditions, wave speed was higher during the pulling action (backward flow) than during the pushing action (forward flow). The amplitudes of pressure and velocity in the pulling action were significantly higher than those in the pushing action. The tube diameter was approximately 20 per cent smaller in the pulling action than in the pushing action in the 16 mm tube. The compression and expansion waves resulting from the pushing and pulling actions dissipated exponentially along the travelling distance, and their dissipation was greater in the smaller than in the larger tubes.

Local wave speed in flexible tubes is flow direction- and wave nature-dependent and is greater with expansion than with compression waves. Wave dissipation has an inverse relationship with the vessel diameter, and dissipation of the expansion wave of the pulling action was greater than that of the pushing action.
Fast algorithm for real-time torque estimation
Authors: Stotsky A
Published: June 2008

A new computationally efficient filtering algorithm based on the Kaczmarz projection method for reconstruction of the first harmonic of a periodic signal is presented. The algorithm makes it possible to recover the combustion quality information from engine speed measurements that are noise contaminated. The algorithm is verified by using a spark ignition six-cylinder engine in the torque estimation problem.
Credit Elasticities in Less-Developed Economies: Implications for Microfinance
Authors: Karlan Dean S , Zinman Jonathan
Published: June 2008

Policymakers often prescribe that microfinance institutions increase interest rates to eliminate their reliance on subsidies. This strategy makes sense if the poor are rate insensitive: then microlenders increase profitability (or achieve sustainability) without reducing the poor's access to credit. We test the assumption of price inelastic demand using randomized trials conducted by a consumer lender in South Africa. The demand curves are downward sloping, and steeper for price increases relative to the lender's standard rates. We also find that loan size is far more responsive to changes in loan maturity than to changes in interest rates, which is consistent with binding liquidity constraints. (JEL G21, O16)
The Interaction of Public and Private Insurance: Medicaid and the Long-Term Care Insurance Market
Authors: Brown Jeffrey R , Finkelstein Amy
Published: June 2008

We show that even incomplete public insurance can crowd out private insurance demand. We estimate that Medicaid could explain the lack of private long-term care insurance for about two-thirds of the wealth distribution, even if no other factors limited the market's size. Yet Medicaid provides incomplete consumption smoothing for most individuals. Medicaid's crowd-out effect stems from the large implicit tax (about 60–75 percent for a median-wealth individual) that Medicaid imposes on private insurance. An implication is that public policies designed to stimulate the private insurance market will have limited efficacy as long as Medicaid's large implicit tax remains. (JEL G22, I18, I38)
Strotz Meets Allais: Diminishing Impatience and the Certainty Effect
Authors: Halevy Yoram
Published: June 2008

Decision makers tend to exhibit a higher degree of impatience when considering a delay to an immediate reward than when contemplating an identical delay to an equal future reward. This work argues that diminishing impatience originates from the distinction between the certain present and the risky future. A simple functional representation of preferences, exhibiting time inconsistency when the future is uncertain, is derived. Experimental evidence, which is inconsistent with other formulations that account for diminishing impatience, supports the proposed approach. The new theory uncovers a tight relation between diminishing impatience and well-known behavioral regularities in choice under risk and uncertainty. (JEL D12, D81)
Monetary Policy, Judgment, and Near-Rational Exuberance
Authors: Bullard James , Evans George W , Honkapohja Seppo
Published: June 2008

We study how the use of judgment or “add-factors” in macroeconomic forecasting may disturb the set of equilibrium outcomes when agents learn using recursive methods. We examine the possibility of a new phenomenon, which we call exuberance equilibria, in the New Keynesian monetary policy framework. Inclusion of judgment in forecasts can lead to self-fulfilling fluctuations in a subset of the determinacy region. We study how policymakers can minimize the risk of exuberance equilibria. (JEL E17, E31, E52)
Evolution of Time Preference by Natural Selection: Comment
Authors: Robson Arthur J , Szentes Balázs
Published: June 2008

We reexamine Alan R. Rogers' (1994) analysis of the biological basis of the rate of time preference. Although his basic insight concerning the derivation of the utility function holds up, the functional form he uses does not generate equilibrium evolutionary behavior. Moreover, Rogers relies upon an interior solution for a particular kind of intergenerational transfer. We show such interior solutions need not generally arise. Hence Rogers most striking prediction, namely that the real interest rate should be about 2 percent per annum, does not follow. (JEL D11, D91)
Matching with Contracts: Comment
Authors: Hatfield John William , Kojima Fuhito
Published: June 2008

Hatfield and Milgrom (2005) present a unified model of matching with contracts phrased in terms of hospitals and doctors, which subsumes the standard two-sided matching and some package auction models. They show that a stable allocation exists if contracts are substitutes for each hospital. They further claim that if a hospital's preferences violate the substitutes condition, there exist singleton preferences for the other hospitals and doctors such that no stable allocation exists. We show this last claim does not hold in general. We further present a weaker condition that is necessary to guarantee the existence of stable allocations. (JEL C78, D86, J41)
The Difference That CEOs Make: An Assignment Model Approach
Authors: Terviö Marko
Published: June 2008

This paper presents an assignment model of CEOs and firms. The distributions of CEO pay levels and firms' market values are analyzed as the competitive equilibrium of a matching market where talents, as well as CEO positions, are scarce. It is shown how the observed joint distribution of CEO pay and market value can then be used to infer the economic value of underlying ability differences. The variation in CEO pay is found to be mostly due to variation in firm characteristics, whereas implied differences in managerial ability are small and make relatively little difference to shareholder value. (JEL G32, M12, M52)
Default Risk and Income Fluctuations in Emerging Economies
Authors: Arellano Cristina
Published: June 2008

Recent sovereign defaults are accompanied by interest rate spikes and deep recessions. This paper develops a small open economy model to study default risk and its interaction with output and foreign debt. Default probabilities and interest rates depend on incentives for repayment. Default is more likely in recessions because this is when it is more costly for a risk averse borrower to repay noncontingent debt. The model closely matches business cycles in Argentina predicting high volatility of interest rates, higher volatility of consumption relative to output, and negative correlations of output with interest rates and the trade balance. (JEL E21, E23, E32, E43, F34, O11, O19)
Do Wealth Fluctuations Generate Time-Varying Risk Aversion? Micro-Evidence on Individuals' Asset Allocation
Authors: Brunnermeier Markus K , Nagel Stefan
Published: June 2008

We use data from the Panel Study of Income Dynamics to investigate how households' portfolio allocations change in response to wealth fluctuations. Persistent habits, consumption commitments, and subsistence levels can generate time-varying risk aversion with the consequence that when the level of liquid wealth changes, the proportion a household invests in risky assets should also change in the same direction. In contrast, our analysis shows that the share of liquid assets that households invest in risky assets is not affected by wealth changes. Instead, one of the major drivers of household portfolio allocation seems to be inertia: households rebalance only very slowly following inflows and outflows or capital gains and losses. (JEL D14, D31)
Temporary Investment Tax Incentives: Theory with Evidence from Bonus Depreciation
Authors: House Christopher L , Shapiro Matthew D
Published: June 2008

The intertemporal elasticity of investment for long-lived capital goods is nearly infinite. Consequently, investment prices should fully reflect temporary tax subsidies, regardless of the investment supply elasticity. Since prices move one-for-one with the subsidy, elasticities can be inferred from quantities alone. This paper uses a recent tax policy—bonus depreciation—to estimate the investment supply elasticity. Investment in qualified capital increased sharply. The estimated elasticity is high—between 6 and 14. There is no evidence that market prices reacted to the subsidy, suggesting that adjustment costs are internal, or that measurement error masks the price changes. (JEL G31, H32)
How the Electoral College Influences Campaigns and Policy: The Probability of Being Florida
Authors: Strömberg David
Published: June 2008

This paper analyzes how US presidential candidates should allocate resources across states to maximize the probability of winning the election, by developing and estimating a probabilistic-voting model of political competition under the Electoral College system. Actual campaigns act in close agreement with the model. There is a 0.9 correlation between equilibrium and actual presidential campaign visits across states, both in 2000 and 2004. The paper shows how presidential candidate attention is affected by the states' number of electoral votes, forecasted state-election outcomes, and forecast uncertainty. It also analyzes the effects of a direct national popular vote for president. (JEL D72)
Do People Vote with Their Feet? An Empirical Test of Tiebout's Mechanism
Authors: Banzhaf H. Spencer , Walsh Randall P
Published: June 2008

Charles Tiebout's suggestion that people “vote with their feet” for communities with optimal bundles of taxes and public goods has played a central role in local public finance for over 50 years. Using a locational equilibrium model, we derive formal tests of his premise. The model predicts increased population density in neighborhoods experiencing exogenous improvements in public goods and, for large improvements, increased relative mean incomes. We test these hypotheses in the context of changing air quality. Our results provide strong empirical support for the notion that households “vote with their feet” for environmental quality. (JEL H41, H73, Q53, R23)
Thar She Blows: Can Bubbles Be Rekindled with Experienced Subjects?
Authors: Hussam Reshmaan N , Porter David , Smith Vernon L
Published: June 2008

We report 28 new experiment sessions consisting of up to three experience levels to examine the robustness of learning and “error” elimination among participants in a laboratory asset market and its effect on price bubbles. Our answer to the title question is: “yes.” We impose a large increase in liquidity and dividend uncertainty to shock the environment of experienced subjects who have converged to equilibrium, and this treatment rekindles a bubble. However, in replications of that same challenging environment across three experience levels, we discover that the environment yields a rare residual tendency to bubble even in the third experience session. Therefore, a caveat must be placed on the effect of twice-experienced subjects in asset markets: in order for price bubbles to be extinguished, the environment in which the participants engage in exchange must be stationary and bounded by a range of parameters. Experience, including possible “error” elimination, is not robust to major new environment changes in determining the characteristics of a price bubble. (JEL C91, D83)
Pride and Prejudice: The Human Side of Incentive Theory
Authors: Ellingsen Tore , Johannesson Magnus
Published: June 2008

Desire for social esteem is a source of prosocial behavior. We develop a model in which actors' utility of esteem depends on the audience. In a principal-agent setting, we show that the model can account for motivational crowding out. Control systems and pecuniary incentives erode morale by signaling to the agent that the principal is not worth impressing. The model also offers an explanation for why agents are motivated by unconditionally high pay and by mission-oriented principals. (JEL D01, D82)
Mathematical Programming Algorithms for Two-Path Routing Problems with Reliability Considerations
Authors: Andreas April K. , Smith J. Cole
Published: June 2008

Most traditional routing problems assume perfect operability of all arcs and nodes. However, when independent arc failure probabilities exist, a secondary objective must be present to retain some measure of expected functionality, introducing nonlinear, nonconvex constraints. We examine the robust two-path problem, which seeks to establish two paths between a source and destination node wherein at least one path must remain fully operable with some threshold probability. We consider the case where both paths must be arc disjoint and the case where arcs can be shared between the paths. We examine various strategies for solving the resulting nonlinear integer program, including pruning, coefficient tightening, lifting, and branch-and-bound partitioning schemes. We discuss the advantages and disadvantages of these methods and conclude with computational results.
Marketspace or Marketplace? Online Information Search and Channel Outcomes in Auto Retailing
Authors: Kuruzovich Jason , Viswanathan Siva , Agarwal Ritu , Gosain Sanjay , Weitzman Scott
Published: June 2008

The growth of the Internet has spawned an increasing number of online information sources (OISs). The effect of OISs on consumer information search processes has been particularly striking in sectors such as auto retailing, where the typical consumer has conventionally been confronted with an unpleasant and inefficient purchase process. However, the relationships between the information found in the online “marketspace,” consumer search in the offline “marketplace,” and other aspects of the multichannel shopping process are not well understood. This study examines the differential impact of price and product information found in the marketspace, relating consumers' information needs and information retrieval from OISs to three shopping-related outcomes—purchase based on online infomediary referral (i.e., referred purchase), intensity of search in the marketplace, and online search satisfaction. We draw on a large data set of more than 16,000 new vehicle purchasers who reported using the Web for search related to their new vehicle purchase. We find that OISs offer different levels of price and product information and consumers are differentiated in their ability to retrieve this information. Further, the retrieval of price versus product information online has important implications for whether consumers consummate their online search through referred purchase or extend their search into the physical marketplace. Our results suggest different business models for infomediaries providing price and product information and underscore the need for designing information provisioning systems of OISs to facilitate transition between the marketspace and the marketplace.
Research Note—Awareness Displays and Social Motivation for Coordinating Communication
Authors: Dabbish Laura , Kraut Robert
Published: June 2008

Researchers and designers have been building awareness displays to improve the coordination of communication between distributed co-workers since the early 1990s. Awareness displays are technology designed to provide contextual information about the activities of group members. Most researchers have assumed that these displays improve the coordination of communication regardless of the relationship between the communicating parties. This article examines the conditions under which awareness displays improve coordination and the types of designs that most effectively support communication timing without overwhelming people with irrelevant information. Results from a pair of laboratory experiments indicate that awareness displays containing information about a remote collaborator's workload lead to communication attempts that are less disruptive, but only when the interrupter has incentives to be concerned about the collaborator's welfare. High-information awareness displays harmed interrupters' task performance, while abstract displays did not. We conclude that a display with an abstract representation of a collaborator's workload is optimal; it leads to better timing of interruptions without overwhelming the person viewing the display.
Contingency Theory and Public Bureaucracies
Authors: Greenwood Royston , Hinings C.R.
Published: June 2008

The study of organizational bureaucracies has in recent years taken the form of ‘contingency theory’ a theory which rests upon the assumption that organizational characteristics have to be shaped to meet situational circumstances. The theory implies that the extent to which an organization secures a ‘goodness of fit’ between situational circumstances and structural characteristics will determine the level of organizational performance. Child summarizes it as follows: contingency theory ‘regards the design of an effective organization as necessarily having to be adapted to cope with the “contingencies” which derive from the circumstances of environment, technology, scale, resources and other factors in the situation in which an organization is operating’.

It is interesting that not one of the major contributions to contingency theory has considered the existence of elected representatives, to whom an organization is subordinated, and who are themselves accountable to a wider electorate, as being a significant contingency operating upon government bureaucracies. Blau has studied several government agencies in the United States, covering personnel agencies finance departments and employment security agencies; Meyer examined finance authorities; Hage and Aiken studied sixteen social welfare agencies; Hall and Pugh et al. covered both public and private bureaucracies.
Rapid Nondestructive On-Site Screening of Methylamphetamine Seizures by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy
Authors: Goh Ching Yong , Van Bronswijk Wilhelm , Priddis Colin
Published: June 2008

The identification and quantification of illicit substances in the field is often desirable. Fourier transform infrared spectroscopy (FT-IR) has both qualitative and quantitative capabilities and field portable instruments are commercially available. Transmission infrared spectra of mixtures containing ephedrine hydrochloride, glucose, and caffeine and attenuated total reflection (ATR) infrared spectra of mixtures composed of methylamphetamine hydrochloride, glucose, and caffeine were used to develop principal component regression (PCR) calibration models. The root mean sum of errors of predictions (RMSEP) of all individual components in a mixture from a single measurement was <6% w/w, which reduced to ∼3% w/w when triplicates were averaged. Sample mixing and grinding are essential to minimize the effect of heterogeneity, as deviations of up to 20% w/w were observed for single measurements of unground samples. Poor predictions of the components in a mixture occurred when samples were “contaminated” with substances not present in the calibration set, as would be expected. When only a single analyte (drug) was targeted, using a calibration set that contained both contaminated and uncontaminated samples, an RMSEP of ∼4% w/w was achieved. The results demonstrate that ATR-FT-IR has the potential to quantify methylamphetamine samples, and possibly other licit or illicit substances, in at-seizure and on-site scenarios.
Micro Attenuated Total Reflection Spectra of Bulk Silica Glass: Effects of Experimental Conditions and Glass Thermal History on Appearance of a Surface Polariton in the Si—O Stretching Region
Authors: Stolov Andrei A. , Simoff Debra A.
Published: June 2008

Micro attenuated total reflection (micro-ATR) spectra of bulk silica glass were investigated for a variety of samples, including fused quartz slides, an optical fiber preform, and a series of optical fiber claddings. The experiments were performed at varied distances between the internal reflection element (IRE) and the sample. At certain conditions, a surface polariton peak is observed in the region 1100–1160 cm−1. The position of this peak is affected by the type of IRE (Ge, Si, ZnSe, or diamond), IRE–sample distance, and the material used as an interlayer between the IRE and the sample (air or Nujol). From the experimental data, the dielectric constant of silica is determined in the region between 1100 and 1160 cm−1. The polariton peak is also observed when glass is coated with a thin (40 nm) layer of carbon. It has also been found that the polariton peak position is affected by the thermal history of the glass, and an attempt is made to correlate the observed changes with the glass fictive temperature.
Fourier Transform Infrared Measurement of Solid-, Liquid-, and Gas-Phase Samples with a Single Photoacoustic Cell
Authors: Uotila Juho , Kauppinen Jyrki
Published: June 2008

A photoacoustic detector based on the optical cantilever microphone has been built. The detector is capable of measuring solid-, liquid-, and gas-phase samples. Photoacoustic Fourier transform infrared (FT-IR) measurement with three samples in different phases was demonstrated. Example samples were polyethene, sunflower oil, and methane. The sensitivity of the cell was compared to a commercial photoacoustic FT-IR detector. With the standard carbon black sample the cantilever detector gave approximately five times higher signal-to-noise ratio than the reference detector. The sensitivity with methane was also compared to the DTGS detector of the FT-IR instrument corresponding to an absorption path of 6.3 cm. Simulation of the photoacoustic signal showed that a compromise has to be made in the cell design between sensitivity for solid- and gas-phase samples but it is possible to highly enhance the sensitivity for all types of samples by reducing cantilever dimensions.