We Are Not You - But We Are Part of What You Are - And What You Will Be, Address to the Council of the AICPA, May 8, 1973 - Colorado Springs, Colorado

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Monte Carlo simulations of dissipative quantum Ising models

The dynamical critical exponent $z$ is a fundamental quantity in characterizing quantum criticality, and it is well known that the presence of dissipation in a quantum model has significant impact on the value of $z$. Studying quantum Ising spin models using Monte Carlo methods, we estimate the dynamical critical exponent $z$ and the correlation length exponent $\nu$ for different forms of dissipation. For a two-dimensional quantum Ising model with Ohmic site dissipation, we find $z \approx 2$ as for the corresponding one-dimensional case, whereas for a one-dimensional quantum Ising model with Ohmic bond dissipation we obtain the estimate $z \approx 1$.Comment: 9 pages, 8 figures. Submitted to Physical Review

Reconstructing the phylogeny and characterizing the patterns of molecular evolution of the tetraploid freshwater suckers (Cypriniformes: Catostomidae)

The Catostomidae, colloquially known as the suckers, is a family of freshwater fish endemic to North America and Asia. This family is hypothesized to have evolved sometime before or during the Paleocene (56-66 Mya) from a single tetraploid ancestor, which is thought to be the product of a hybridization event between two closely related, diploid cypriniforms. Currently, there are 79 recognized, extant species, some of which are difficult to discriminate between in the field. Despite the numerous studies that have aimed to reconstruct the evolutionary history of this family, little consensus exists for the relationships of the subfamilies within the Catostomidae, with practically every combination of subfamilial relationships having been proposed in the past. Additionally, and of importance to our understanding of the evolution of the catostomids, little is still known about the consequences of whole genome duplication on molecular evolution, especially for polyploid animals. In this study, we sought to reconstruct the evolutionary history of the Catostomidae as well as characterize the patterns of molecular evolution of lineages within this family. Two nucleotide sequence, genome-scale data sets were generated with the aim to reconstruct the evolutionary history of the Catostomidae as well as characterize patterns of molecular evolution of their polyploid genomes. These data sets, an unphased data including one sequence for each taxon and a phased data with the number of sequences per taxon representative of their ploidy level, included 179 and 267 loci, respectively. From the reconstruction of the evolutionary history of the family, we recovered a topology which places Myxocyprinus asiaticus as the sister taxon to all other extant catostomids and Cycleptus elongatus as the sister taxon to an Ictiobinae + Catostominae clade. Additionally, we found that Catostomus was recovered as paraphyletic, with Deltistes luxatus, Chasmistes liorus, and Xyrauchen texanus forming strongly supported sister species relationships with species within Catostomus. In the second chapter, we found that the ictiobines, cycleptines, and myxocyprinines tended to have more polymorphic alleles than taxa within Catostominae. We also found that rates of molecular evolution were significantly greater within catostomine lineages than all other catostomid lineages

Criticality of compact and noncompact quantum dissipative Z4Z_4 models in (1+1)(1+1) dimensions

Using large-scale Monte Carlo computations, we study two versions of a $(1+1)D$ $Z_4$-symmetric model with Ohmic bond dissipation. In one of these versions, the variables are restricted to the interval $[0,2\pi>$, while the domain is unrestricted in the other version. The compact model features a completely ordered phase with a broken $Z_4$ symmetry and a disordered phase, separated by a critical line. The noncompact model features three phases. In addition to the two phases exhibited by the compact model, there is also an intermediate phase with isotropic quasi-long-range order. We calculate the dynamical critical exponent $z$ along the critical lines of both models to see if the compactness of the variable is relevant to the critical scaling between space and imaginary time. There appears to be no difference between the two models in that respect, and we find $z\approx1$ for the single phase transition in the compact model as well as for both transitions in the noncompact model

Quantum criticality in spin chains with non-ohmic dissipation

We investigate the critical behavior of a spin chain coupled to bosonic baths characterized by a spectral density proportional to $\omega^s$, with $s>1$. Varying $s$ changes the effective dimension $d_\text{eff} = d + z$ of the system, where $z$ is the dynamical critical exponent and the number of spatial dimensions $d$ is set to one. We consider two extreme cases of clock models, namely Ising-like and U(1)-symmetric ones, and find the critical exponents using Monte Carlo methods. The dynamical critical exponent and the anomalous scaling dimension $\eta$ are independent of the order parameter symmetry for all values of $s$. The dynamical critical exponent varies continuously from $z \approx 2$ for $s=1$ to $z=1$ for $s=2$, and the anomalous scaling dimension evolves correspondingly from $\eta \gtrsim 0$ to $\eta = 1/4$. The latter exponent values are readily understood from the effective dimensionality of the system being $d_\text{eff} \approx 3$ for $s=1$, while for $s=2$ the anomalous dimension takes the well-known exact value for the 2D Ising and XY models, since then $d_{\rm{eff}}=2$. A noteworthy feature is, however, that $z$ approaches unity and $\eta$ approaches 1/4 for values of $s < 2$, while naive scaling would predict the dissipation to become irrelevant for $s=2$. Instead, we find that $z=1,\eta=1/4$ for $s \approx 1.75$ for both Ising-like and U(1) order parameter symmetry. These results lead us to conjecture that for all site-dissipative $Z_q$ chains, these two exponents are related by the scaling relation $z = \text{max} {(2-\eta)/s, 1}$. We also connect our results to quantum criticality in nondissipative spin chains with long-range spatial interactions.Comment: 8 pages, 6 figure

A Tale of Two Investors: Exploring Differences in Trading Behavior around Macroeconomic Announcements : A study of institutional and retail investors in the US market

We study whether the trading behaviour of institutional and retail investors differs on the days surrounding key macroeconomic announcements, and the impact of this difference on equity premiums earned. Through analysis of trading data from the 50 largest US companies between January 2017 and October 2022, we find a significant difference of 2.11 pp in order imbalances two days prior to announcements. Further, we find a significant difference of 2.06 pp in the equity premiums earned by institutions and retail investors on the day after announcements. We attribute these differences to the higher risk appetite of institutional investors and the slower reaction times and higher attention-sensitivity of retail investors.nhhma

Methodology for Evaluating Grid Development Strategies Considering Real Options and Risks

Traditional power grid planning is based on passive measures such as reinforcing the grid and using present value to compare different grid development plans. However, this approach does not accurately describe the real options value of using active measures, such as energy storage or demand-side load shifting, for postponing grid reinforcement through a “wait-and-see” approach to handle uncertainty in long-term load growth. However, the value of using active measures may come at the price of reducing the security margins in grid operation. This leads to an increased risk of problems during grid operation, and this risk must be weighed against the value of using active measures. This paper presents a methodology for quantifying both the value and risk (or price) of real options related to grid development strategies using active measures, providing grid planners with more comprehensive information about the advantages and disadvantages. The methodology is demonstrated using an illustrative and simple case for a medium voltage reference distribution system, where flexibility from local energy communities is considered as an example of an active measure. The case study illustrates how some risk-taking is required to realize the value from using active measures.Methodology for Evaluating Grid Development Strategies Considering Real Options and RisksacceptedVersio

Rates and Patterns of Evolution in a Duplicated Genome in the Family Catostomidae

Whole genome duplication (WGD) is a process in which the entire genome of an organism is duplicated, making redundant genes which are subject to unique evolutionary forces. Various modes of selection create different genetic fates such as retention of ancestral function, development of new function, or loss of function. Because of these differing fates, WGD is hypothesized to be a major driving force behind diversification. In this project, DNA sequences from fish species in the family Catostomidae were examined to observe patterns of evolution following a known WGD. Gene trees were generated for 179 loci to determine the amount of divergence among duplicates, revealing divergence to be more common than conservation. Time calibrated phylogenies were generated revealing the date of initial duplicate divergence within the subfamily Ictiobinae to be approximately 63 MYA. Further analysis could reveal the evolutionary fate of each loci, providing insight into the ways WGD affects diversification