An Investigation of Firm Heterogeneity in the Constraints to Development and Growth in Pakistan

This study considers the importance of firm characteristics in explaining the degree of business constraints facing Pakistani firms in the Investment Climate Survey. We quantify how firms with differing characteristics experience particular problems. After controlling for other factors, the largest differences in responses to business constraints occur among firms that vary by manufacturing industry, and among firms operating under different ownership structures or selling in different markets. In some cases, firm size and firm location also play an important role. The age of the firm generally does not lead to significant differences. These results account for the heterogeneity of firms better than others, and may be important for policy-makers to develop more specific approaches to fostering the investment climate.Pakistan, Investment Climate, Business Constraints

Electrical read out for coherent phenomena involving Rydberg atoms in thermal vapor cells

We present a very sensitive and scalable method to measure the population of highly excited Rydberg states in a thermal vapor cell of rubidium atoms. We detect the Rydberg ionization current in a 5 mm electrically contacted cell. The measured current is found to be in excellent agreement with a theory for the Rydberg population based on a master equation for the three level problem including an ionization channel and the full Doppler distributions at the corresponding temperatures. The signal-to-noise ratio of the current detection is substantially better than purely optical techniques.Comment: 4 pages, 4 figure

Effect of a unilateral hind limb orthotic lift on upper body movement symmetry in the trotting horse

In trotting horses, movement asymmetry is associated with ground reaction force asymmetry. In humans, limb length differences influence contralateral force production. Here we investigate whether horses, in immediate reaction to limb length changes, show movement asymmetry adaptations consistent with reported force differences. Aim of this study was to quantify pelvic and compensatory head and withers movement asymmetry as a function of limb length changes after application of orthotic lifts. In this experimental study movement asymmetry of eleven trotting horses was calculated from vertical displacement of poll, withers, sacrum and left and right tuber coxae with inertial sensors. Horses were assessed in-hand under 5 conditions (all with hind limb boots): without orthotic lifts, and with a 15mm or 30mm orthotic lift applied to the left hind or right hind. A linear mixed model investigated the influence of orthotic lift condition (P<0.05, pairwise posthoc Bonferroni correction). Pelvic movement asymmetry showed increased pelvic downward movement during stance of the shorter limb and increased pelvic upward movement during and after stance of the longer limb (P<0.001) with asymmetry changes of 3-7mm (4-10mm) for 15mm (30mm) lifts. Hip hike (tuber coxae movement asymmetry) was unaffected (P = 0.348). Head and withers movement asymmetry were affected less consistently (2 of 3 respectively 1 of 3 head or withers parameters). The small sample size of the study reduced generalizability, no direct force measurements were conducted and only immediate effects of orthotic lifts were assessed with no re-assessments days or weeks after. Conclusions about mechanical consequences (weight bearing, pushoff) are based on published movement-force associations. Pelvic movement asymmetry with an artificial change in limb length through application of an orthotic lift indicates increased weight support with the shorter limb and increased pushoff with the longer limb. This may be of relevance for the management of horses with different hoof shapes between contralateral limbs, for example some chronically lame horse

Cascade of magnetic field induced Lifshitz transitions in the ferromagnetic Kondo lattice material YbNi4P2

A ferromagnetic quantum critical point is thought not to exist in two and three-dimensional metallic systems yet is realized in the Kondo lattice compound YbNi4(P,As)2, possibly due to its one-dimensionality. It is crucial to investigate the dimensionality of the Fermi surface of YbNi4P2 experimentally but common probes such as ARPES and quantum oscillation measurements are lacking. Here, we studied the magnetic field dependence of transport and thermodynamic properties of YbNi4P2. The Kondo effect is continuously suppressed and additionally we identify nine Lifshitz transitions between 0.4 and 18 T. We analyze the transport coefficients in detail and identify the type of Lifshitz transitions as neck or void type to gain information on the Fermi surface of YbNi4P2. The large number of Lifshitz transitions observed within this small energy window is unprecedented and results from the particular flat renormalized band structure with strong 4f-electron character shaped by the Kondo lattice effect.Comment: 6 pages, 4 figure

Strongly correlated growth of Rydberg aggregates in a vapor cell

The observation of strongly interacting many-body phenomena in atomic gases typically requires ultracold samples. Here we show that the strong interaction potentials between Rydberg atoms enable the observation of many-body effects in an atomic vapor, even at room temperature. We excite Rydberg atoms in cesium vapor and observe in real-time an out-of-equilibrium excitation dynamics that is consistent with an aggregation mechanism. The experimental observations show qualitative and quantitative agreement with a microscopic theoretical model. Numerical simulations reveal that the strongly correlated growth of the emerging aggregates is reminiscent of soft-matter type systems

Determination of the s-wave Scattering Length of Chromium

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes $^{52}$Cr and $^{50}$Cr. From the time constants for cross-dimensional thermalization in atomic samples we have determined the magnitudes $|a(^{52}Cr)|=(170 \pm 39)a_0$ and $|a(^{50}Cr)|=(40 \pm 15)a_0$, where $a_0=0.053nm$. By measuring the rethermalization rate of $^{52}$Cr over a wide temperature range and comparing the temperature dependence with the effective-range theory and single-channel calculations, we have obtained strong evidence that the sign of $a(^{52}Cr)$ is positive. Rescaling our $^{52}$Cr model potential to $^{50}$Cr strongly suggests that $a(^{50}Cr)$ is positive, too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and

Occurrence of Blarina brevicauda in Arkansas and Notes on the Distribution of Blarina carolinensis and Cryptotis parva

We provide an update on the species and distribution of shrews occurring in Arkansas. Shrews were collected within Arkansas Game and Fish Commission Wildlife Management Areas and along the Buffalo National River. We also searched mammal collections at several institutional museums to provide additional locality records for Cryptotis parva. Specimens of Blarina were identified to species by DNA sequencing of the mitochondrial cytochrome b gene. Previously, Blarina hylophaga was believed to occur in the northwest corner of Arkansas and B. carolinensis throughout the rest of the state. However, our genetic analysis revealed that it is B. brevicauda that occupies the northwestern portion of the state. We also document several new county records for B. carolinensis and C. parva in Arkansas

The Portfolio Size Effect and Lifecycle Asset Allocation Funds: A Different Perspective

経済学 / EconomicsBasu and Drew (in the JPM Spring 2009 issue) argue that lifecycle asset allocation strategies are counterproductive to the retirement savings goals of typical individual investors. Because of the portfolio size effect, most portfolio growth will occur in the years just before retirement when lifecycle funds have already switched to a more conservative asset allocation. In this article, we use the same methodology as Basu and Drew, but we do not share their conclusion that the portfolio size effect soundly overturns the justification for the lifecycle asset allocation strategy. While strategies that maintain a large allocation to stocks do provide many attractive features, we aim to demonstrate that a case for supporting a lifecycle strategy can still be made with modest assumptions for risk aversion and diminishing utility from wealth. Our differing conclusion results from four factors: (1) we compare the interactions between different strategies; (2) we consider a more realistic example for the lifecycle asset allocation strategy; (3) we examine the results for 17 countries; and (4) we provide an expected utility framework to compare different strategies. We find that with a very reasonable degree of risk aversion, investors have reason to prefer the lifecycle strategy in spite of the portfolio size effect.JEL Classification Codes: D14, D81, G11, G2

An International Perspective on Safe Withdrawal Rates from Retirement Savings: The Demise of the 4 Percent Rule?

経済学 / EconomicsNumerous studies about sustainable withdrawal rates from retirement savings have been published, but they are overwhelmingly based on the same underlying data for US asset returns since 1926. From an international perspective, the United States enjoyed a particularly favorable climate for asset returns in the twentieth century, and to the extent that the US may experience mean reversion in the current century, sustainable withdrawal rates may be overstated in many studies. This paper explores the issue of sustainable withdrawal rates using 109 years of financial market data for 17 developed market countries in an attempt to provide a broader perspective about sustainable withdrawal rates, as financial planners and their clients must consider whether they will be comfortable basing decisions using the impressive and perhaps anomalous numbers found in the past US data. From an international perspective, a 4 percent real withdrawal rate is surprisingly risky. Even with some overly optimistic assumptions, it would have only provided “safety” in 4 of the 17 countries. A fixed asset allocation split evenly between stocks and bonds would have failed in all 17 countries.JEL Classification Codes: G11, G15, G17, C1