Optimal Policy Intervention and the Social Value of Public Information

Svensson (2006) argues that Morris and Shin (2002) is, contrary to what is claimed, pro-transparency. This paper reexamines the issue but with an important modification to the original Morris and Shin framework. Recognizing that central banks impact the economy not only indirectly via public announcements, but also directly through policy actions, we consider the social value of public information in the presence of active policy intervention. Our results strengthen Morris and Shin's conclusions considerably: in particular, we find that public disclosure of the central bank's information is unambiguously, i.e., regardless of parameter values, undesirable. (JEL D82, D83, E52, E58)

Identification of a Novel 81-kDa Component of the Xenopus Origin Recognition Complex

The Xenopus origin recognition complex is essential for chromosomal DNA replication in cell-free extracts. We have immunopurified the Xenopus origin recognition complex with anti-Xorc2 antibodies and analyzed its composition and properties. Xorc2 (p63) is specifically associated with Xorc1 (p115) and up to four additional polypeptides (p81, p78, p45, and p40). The cDNA encoding p81 is highly homologous to various expressed sequence tags from humans and mice encoding a protein of previously unknown function. Immunodepletion of p81 from Xenopus egg extracts, which also results in the removal of Xorc2, completely abolishes chromosomal DNA replication. Thus, p81 appears to play a crucial role at S phase in higher eukaryotes

Emergent Fermions and Anyons in the Kitaev Model

We study the gapped phase of the Kitaev model on the honeycomb lattice using perturbative continuous unitary transformations. The effective low-energy Hamiltonian is found to be an extended toric code with interacting anyons. High-energy excitations are emerging free fermions which are composed of hardcore bosons with an attached string of spin operators. The excitation spectrum is mapped onto that of a single particle hopping on a square lattice in a magnetic field. We also illustrate how to compute correlation functions in this framework. The present approach yields analytical perturbative results in the thermodynamical limit without using the Majorana or the Jordan-Wigner fermionization initially proposed to solve this problem.Comment: 4 pages, 5 figures, published versio

Negative Cell Cycle Regulation and DNA Damage-inducible Phosphorylation of the BRCT Protein 53BP1

In a screen designed to discover suppressors of mitotic catastrophe, we identified the Xenopus ortholog of 53BP1 (X53BP1), a BRCT protein previously identified in humans through its ability to bind the p53 tumor suppressor. X53BP1 transcripts are highly expressed in ovaries, and the protein interacts with Xp53 throughout the cell cycle in embryonic extracts. However, no interaction between X53BP1 and Xp53 can be detected in somatic cells, suggesting that the association between the two proteins may be developmentally regulated. X53BP1 is modified via phosphorylation in a DNA damage-dependent manner that correlates with the dispersal of X53BP1 into multiple foci throughout the nucleus in somatic cells. Thus, X53BP1 can be classified as a novel participant in the DNA damage response pathway. We demonstrate that X53BP1 and its human ortholog can serve as good substrates in vitro as well as in vivo for the ATM kinase. Collectively, our results reveal that 53BP1 plays an important role in the checkpoint response to DNA damage, possibly in collaboration with ATM

Suppression of Spontaneous Supercurrents in a Chiral p-Wave Superconductor

The superconducting state of SRO is widely believed to have chiral p-wave order that breaks time reversal symmetry. Such a state is expected to have a spontaneous magnetization, both at sample edges and at domain walls between regions of different chirality. Indeed, muon spin resonance experiments are interpreted as evidence of spontaneous magnetization due to domain walls or defects in the bulk. However, recent magnetic microscopy experiments place upper limits on the magentic fields at the sample edge and surface which are as much as two orders of magnitude smaller than the fields predicted theoretically for a somewhat idealized chiral p-wave superconductor. We investigate the effects on the spontaneous supercurrents and magnetization of rough and pair breaking surfaces for a range of parameters within a Ginzburg-Landau formalism. The effects of competing orders nucleated at the surface are also considered. We find the conditions under which the edge currents are significantly reduced while leaving the bulk domain wall currents intact, are quite limited. The implications for interpreting the existing body of experimental results on superconducting SRO within a chiral p-wave model are discussed.Comment: Changes to section 3, typos remove

Discrimination in the Small Business Credit Market

This paper uses data from the 1993 National Survey of Small Business Finances to determine the extent to which minority-owned small businesses face constraints in the credit market beyond those faced by white-owned small businesses. First, we present qualitative evidence indicating that black- and white-owned firms report similar concerns about the factors that may affect their businesses except that blacks are far more likely to report problems with credit availability. Second, we conduct an econometric analysis of loan denial probabilities by race and find that black-owned small businesses are almost three times more likely to have a loan application denied. Even after controlling for the differences in credit-worthiness and other factors that exist between black- and white-owned firms, blacks are still about twice as likely to be denied credit. A series of specification checks indicates that this gap is unlikely to be largely attributed to omitted variable bias. Third, we conduct a similar analysis regarding interest rates charged to approved loans and find black-owned firms pay higher interest rates as well. Finally, even these results are likely to understate differences in credit access because many potential black-owned firms are not in operation due to the lack of credit and those in business may be too afraid to apply. These results indicate that the racial disparity in credit availability is likely caused by discrimination.

Investigating Hydrothermal and Radiation Effects on Nitrogen Heterocycles Relevant to Meteorite Parent Bodies

Organic compounds in meteorites were likely transformed by a variety of processes on the asteroid parent body including aqueous, thermal, and radiolytic alteration. Previous studies have identified a suite of purine nitrogen heterocycles in carbonaceous chondrites (a class of meteorites) and determined that their likely origin was due to cyanide chemistry. The thesis research described here consisted of two parts: investigating thermal effects on aqueous ammonium cyanide reactions and the production/survivability of organics (Chapter 2) and investigating gamma radiation effects on purine nitrogen heterocycles to understand how prolonged radiation exposure influenced the distribution and abundance of nitrogen heterocycles measured in meteorites today (Chapter 3). A temperature study of 1 M ammonium cyanide was conducted from room temperature to 200 °C (temperatures similar to the aqueous alteration of some carbonaceous chondrites) using a high-pressure reaction vessel. The resulting liquid supernatant and water insoluble cyanide (hetero)polymer were isolated and analyzed by attenuated total reflectance Fourier transform infrared spectroscopy and thermochemolysis gas chromatography-mass spectrometry using tetramethylammonium hydroxide or high-performance liquid chromatography with UV detection (HPLC-UV). A strong correlation was observed between thermochemolysis products of cyanide polymers and the initial reaction temperature - production of aromatic compounds increases and nitrogen containing compounds decrease with respect to increasing reaction temperature. The data presented in this thesis suggests that the polymer may be a less efficient source of nitrogen heterocycles when produced at high temperatures. HPLC-UV analysis showed that the supernatant of heated NH4CN reactions is a complex mixture containing many unknown UV-absorbing chromophores. In addition, multiple nitrogen heterocycles were tentatively identified in the supernatant of heated NH4CN reactions including the high temperature 200 °C reactions. Finally, HPLC was used to determine decomposition of seven purine nitrogen heterocycles exposed to gamma radiation from a cobalt-60 source in an effort to extrapolate abundances during the early formation of the Solar System. Generally speaking, purine nitrogen heterocycles in the solid state are very stable to high doses of γ-radiation; however, guanine experienced a 53% decomposition over the course of ~1 MGy of radiation dose. The radiolysis study correlates to similar conditions in asteroids after their initial aqueous alteration period (i.e. dry alteration) and suggests that meteorite abundances for some compounds (such as adenine) may have remained relatively unchanged over time, but other compounds (like guanine) may have had “original” abundances greater than those currently observed in carbonaceous chondrites

Glassy Phase of Optimal Quantum Control

We study the problem of preparing a quantum many-body system from an initial to a target state by optimizing the fidelity over the family of bang-bang protocols. We present compelling numerical evidence for a universal spin-glass-like transition controlled by the protocol time duration. The glassy critical point is marked by a proliferation of protocols with close-to-optimal fidelity and with a true optimum that appears exponentially difficult to locate. Using a machine learning (ML) inspired framework based on the manifold learning algorithm t-SNE, we are able to visualize the geometry of the high-dimensional control landscape in an effective low-dimensional representation. Across the transition, the control landscape features an exponential number of clusters separated by extensive barriers, which bears a strong resemblance with replica symmetry breaking in spin glasses and random satisfiability problems. We further show that the quantum control landscape maps onto a disorder-free classical Ising model with frustrated nonlocal, multibody interactions. Our work highlights an intricate but unexpected connection between optimal quantum control and spin glass physics, and shows how tools from ML can be used to visualize and understand glassy optimization landscapes.Comment: Modified figures in appendix and main text (color schemes). Corrected references. Added figures in SI and pseudo-cod