The impact of financing constraints on investment.

This thesis is an empirical and theoretical analysis of the impact of financing constraints on firm-level investment behaviour. Its primary objectives are to model this impact, and to test the restrictions these models place on the data. Chapter 1 contains a discussion of these themes, and provides an overview of the thesis. Chapter 2 addresses the empirical question of whether innovative firms are financially constrained. To answer this question, several structural investment equations are tested, and the sensitivity of physical investment expenditures to internal finance is compared across innovative and non-innovative firms. The investment expenditures of innovative firms are found to be more sensitive to cash flow than those of non-innovative firms. These results support the hypothesis that innovative firms are financially constrained. The third chapter builds a theoretical model to explain a widely reported fact in the inventory literature, which is that the variance of production exceeds the variance of sales. This fact contradicts a prediction of the standard Linear-Quadratic model of inventory investment, and for this reason is often referred to as the "excess variance of production" puzzle. In this chapter, a model of inventory investment is built. It is shown that when financing constraints are imposed on the model, it can explain the excess variance of production puzzle. In the absence of these constraints, the model does not deliver this result. The fourth chapter returns to the theme of identifying financially constrained firms. A weakness of existing tests of financing constraints is that they are not both direct and structural. This chapter addresses that criticism by constructing a model of investment from which is derived a simple and direct, structural test of the null hypothesis that a group of firms is financially constrained. The test is implemented on a panel of U.S. manufacturing firms. The results support the findings of existing tests

Non trivial generalizations of the Schwinger pair production result

We present new, non trivial generalizations of the recent Tomaras, Tsamis and Woodard extension of the original Schwinger formula for charged pair production in a constant field.Comment: 11 page

Temperature dependence of the Casimir effect between metallic mirrors

We calculate the Casimir force and free energy for plane metallic mirrors at non-zero temperature. Numerical evaluations are given with temperature and conductivity effects treated simultaneously. The results are compared with the approximation where both effects are treated independently and the corrections simply multiplied. The deviation between the exact and approximated results takes the form of a temperature dependent function for which an analytical expression is given. The knowledge of this function allows simple and accurate estimations at the % level.Comment: 8 pages, 4 figures, uses RevTe

Perceived Noise Analysis for Offset Jets Applied to Commercial Supersonic Aircraft

A systems analysis was performed with experimental jet noise data, engine/aircraft performance codes and aircraft noise prediction codes to assess takeoff noise levels and mission range for conceptual supersonic commercial aircraft. A parametric study was done to identify viable engine cycles that meet NASA's N+2 goals for noise and performance. Model scale data from offset jets were used as input to the aircraft noise prediction code to determine the expected sound levels for the lateral certification point where jet noise dominates over all other noise sources. The noise predictions were used to determine the optimal orientation of the offset nozzles to minimize the noise at the lateral microphone location. An alternative takeoff procedure called "programmed lapse rate" was evaluated for noise reduction benefits. Results show there are two types of engines that provide acceptable mission range performance; one is a conventional mixed-flow turbofan and the other is a three-stream variable-cycle engine. Separate flow offset nozzles reduce the noise directed toward the thicker side of the outer flow stream, but have less benefit as the core nozzle pressure ratio is reduced. At the systems level for a three-engine N+2 aircraft with full throttle takeoff, there is a 1.4 EPNdB margin to Chapter 3 noise regulations predicted for the lateral certification point (assuming jet noise dominates). With a 10% reduction in thrust just after clearing the runway, the margin increases to 5.5 EPNdB. Margins to Chapter 4 and Chapter 14 levels will depend on the cumulative split between the three certification points, but it appears that low specific thrust engines with a 10% reduction in thrust (programmed lapse rate) can come close to meeting Chapter 14 noise levels. Further noise reduction is possible with engine oversizing and derated takeoff, but more detailed mission studies are needed to investigate the range impacts as well as the practical limits for safety and takeoff regulations

Hamiltonian BRST deformation of a class of n-dimensional BF-type theories

Consistent Hamiltonian interactions that can be added to an abelian free BF-type class of theories in any n greater or equal to 4 spacetime dimensions are constructed in the framework of the Hamiltonian BRST deformation based on cohomological techniques. The resulting model is an interacting field theory in higher dimensions with an open algebra of on-shell reducible first-class constraints. We argue that the Hamiltonian couplings are related to a natural structure of Poisson manifold on the target space.Comment: 27 pages, uses JHEP3.cl

Association of child maltreatment with risk of death during childhood in South Australia

Importance Child maltreatment is a prominent public health concern affecting 20% to 50% of children worldwide. Consequences for mental and physical health have been reported, but population-level estimates of risk of death during childhood that are adjusted for confounders have not been published to date. Objective To estimate the association of documented child protection concerns regarding maltreatment with risk of death from infancy to 16 years of age. Design, setting, and participants This case-control study was nested in a population birth cohort of 608 547 persons born in South Australia, Australia. Case children were those who died between 1 month and 16 years of age (with the death registered by May 31, 2019). Control children were randomly selected individuals from the same population who were alive at the age at which the case child died, matched 5:1 for age, sex, and Aboriginal status. Data were analyzed from January 2019 to March 2021. Exposure Children were assigned to 1 of 4 child protection concern categories (child protection system notification[s] only, investigation[s] [not substantiated], substantiated maltreatment, and ever placed in out-of-home care) based on administrative data from the South Australia Department for Child Protection or were classified as unexposed.Main outcomes and measures Mortality rate ratios for death before 16 years of age, by child protection concern category, were estimated using conditional logistic regression, adjusted for birth outcomes, maternal attributes, and area-based socioeconomic status. Patterns of cause of death were compared for children with vs without child protection concerns.Results Of 606 665 children included in the study, 1635 were case children (57.9% male [when sex was known]; mean [SD] age, 3.59 [4.56] years) and 8175 were control children (57.7% male; mean [SD] age, 3.59 [4.56] years [age censored at the time of death of the matched control child]). Compared with children with no child protection system contact, adjusted mortality rate ratios among children who died before 16 years of age were 2.69 (95% CI, 2.05-3.54) for children with child protection system notification(s) only; 3.16 (95% CI, 2.25-4.43) for children with investigation(s) (not substantiated); 2.93 (95% CI, 1.95-4.40) with substantiated maltreatment; and 3.79 (95% CI, 2.46-5.85) for children ever placed in out-of-home care. External causes represented 136 of 314 deaths (43.3%) among children with a documented child protection concern and 288 of 1306 deaths (22.1%) among other children. Deaths from assault or self-harm were most overrepresented, accounting for 11.1% of deaths in children with child protection concerns but just 0.8% of deaths among other children. Conclusions and relevance In this case-control study, children with documented child protection concerns, who were known to child protection agencies and were typically seen by clinicians and other service providers, had a higher risk of death compared with children with no child protection service contact. These findings suggest the need for a more comprehensive service response for children with protection concerns.Leonie Segal, James Doidge, Jason M. Armfield, Emmanuel S. Gnanamanickam, David B. Preen, Derek S. Brown, Ha Nguye

A 750 mW, continuous-wave, solid-state laser source at 313 nm for cooling and manipulating trapped 9Be+ ions

We present a solid-state laser system that generates 750 mW of continuous-wave single-frequency output at 313 nm. Sum-frequency generation with fiber lasers at 1550 nm and 1051 nm produces up to 2 W at 626 nm. This visible light is then converted to UV by cavity-enhanced second-harmonic generation. The laser output can be tuned over a 495 GHz range, which includes the 9Be+ laser cooling and repumping transitions. This is the first report of a narrow-linewidth laser system with sufficient power to perform fault-tolerant quantum-gate operations with trapped 9Be+ ions by use of stimulated Raman transitions.Comment: 9 pages, 4 figure

Microwave-induced control of Free Electron Laser radiation

The dynamical response of a relativistic bunch of electrons injected in a planar magnetic undulator and interacting with a counterpropagating electromagnetic wave is studied. We demonstrate a resonance condition for which the free electron laser (FEL) dynamics is strongly influenced by the presence of the external field. It opens up the possibility of control of short wavelength FEL emission characteristics by changing the parameters of the microwave field without requiring change in the undulator's geometry or configuration. Numerical examples, assuming realistic parameter values analogous to those of the TTF-FEL, currently under development at DESY, are given for possible control of the amplitude or the polarization of the emitted radiation.Comment: 14 pages, 5 figures, accepted for publication in Phys. Rev.

Renormalization Group and Decoupling in Curved Space: II. The Standard Model and Beyond

We continue the study of the renormalization group and decoupling of massive fields in curved space, started in the previous article and analyse the higher derivative sector of the vacuum metric-dependent action of the Standard Model. The QCD sector at low-energies is described in terms of the composite effective fields. For fermions and scalars the massless limit shows perfect correspondence with the conformal anomaly, but similar limit in a massive vector case requires an extra compensating scalar. In all three cases the decoupling goes smoothly and monotonic. A particularly interesting case is the renormalization group flow in the theory with broken supersymmetry, where the sign of one of the beta-functions changes on the way from the UV to IR.Comment: 27 pages, 8 figure

Thomson and Compton scattering with an intense laser pulse

Our paper concerns the scattering of intense laser radiation on free electrons and it is focused on the relation between nonlinear Compton and nonlinear Thomson scattering. The analysis is performed for a laser field modeled by an ideal pulse with a finite duration, a fixed direction of propagation and indefinitely extended in the plane perpendicular to it. We derive the classical limit of the quantum spectral and angular distribution of the emitted radiation, for an arbitrary polarization of the laser pulse. We also rederive our result directly, in the framework of classical electrodynamics, obtaining, at the same time, the distribution for the emitted radiation with a well defined polarization. The results reduce to those established by Krafft et al. [Phys. Rev. E 72, 056502 (2005)] in the particular case of linear polarization of the pulse, orthogonal to the initial electron momentum. Conditions in which the differences between classical and quantum results are visible are discussed and illustrated by graphs