Quantitative Assessment of the Anatomical Footprint of the C1 Pedicle Relative to the Lateral Mass: A Guide for C1 Lateral Mass Fixation

Study Design: Anatomic study. Objectives: To determine the relationship of the anatomical footprint of the C1 pedicle relative to the lateral mass (LM). Methods: Anatomic measurements were made on fresh frozen human cadaveric C1 specimens: pedicle width/height, LM width/height (minimum/maximum), LM depth, distance between LM’s medial aspect and pedicle’s medial border, distance between LM’s lateral aspect to pedicle’s lateral border, distance between pedicle’s inferior aspect and LM’s inferior border, distance between arch’s midline and pedicle’s medial border. The percentage of LM medial to the pedicle and the distance from the center of the LM to the pedicle’s medial wall were calculated. Results: A total of 42 LM were analyzed. The C1 pedicle’s lateral aspect was nearly confluent with the LM’s lateral border. Average pedicle width was 9.0 ± 1.1 mm, and average pedicle height was 5.0 ± 1.1 mm. Average LM width and depth were 17.0 ± 1.6 and 17.2 ± 1.6 mm, respectively. There was 6.9 ± 1.5 mm of bone medial to the medial C1 pedicle, which constituted 41% ± 9% of the LM’s width. The distance from C1 arch’s midline to the medial pedicle was 13.5 ± 2.0 mm. The LM’s center was 1.6 ± 1 mm lateral to the medial pedicle wall. There was on average 3.5 ± 0.6 mm of the LM inferior to the pedicle inferior border. Conclusions: The center of the lateral mass is 1.6 ± 1 mm lateral to the medial wall of the C1 pedicle and approximately 15 mm from the midline. There is 6.9 ± 1.5 mm of bone medial to the medial C1 pedicle. Thus, the medial aspect of C1 pedicle may be used as an anatomic reference for locating the center of the C1 LM for screw fixation

Nonequilibrium relaxation and scaling properties of the two-dimensional Coulomb glass in the aging regime

We employ Monte Carlo simulations to investigate the two-time density autocorrelation function for the two-dimensional Coulomb glass. We find that the nonequilibrium relaxation properties of this highly correlated disordered system can be described by a full aging scaling ansatz. The scaling exponents are non-universal, and depend on temperature and charge density.Comment: 6 pages, 3 figures included; revised version: corrected exponents, and some additional explanations and references added; to appear in EP

Space and Time in Macroeconomic Panel Data: Young Workers and State-Level Unemployment Revisited

A provocative paper by Shimer (2001) finds that state-level youth shares and unemployment rates are negatively correlated, in contrast to conventional assumptions about demographic effects on labor markets. This paper updates Shimer's regressions and shows that this surprising correlation essentially disappears when the end of the sample period is extended from 1996 to 2005. This shift does not occur because of a change in the underlying economy during the past decade. Rather, the presence of a cross-sectional (that is, spatial) correlation in the state-level data sharply reduces the precision of the earlier estimates, so that the true standard errors are several times larger than those originally reported. Using a longer sample period and some controls for spatial correlation in the regression, point estimates for the youth-share effect on unemployment are positive and close to what a conventional model would imply. Unfortunately, the standard errors remain very large. The difficulty of obtaining precise estimates with these data illustrates a potential pitfall in the use of regional panel data for macroeconomic analysis

Job Flows, Demographics and the Great Recession

The recession the United States economy entered in December of 2007 is considered to be the most severe downturn the country has experienced since the Great Depression. The unemployment rate reached as high as 10.1 percent in October 2009 - the highest we have seen since the 1982 recession. In this paper we examine the severity of this recession compared to those in the past by examining worker flows into and out of unemployment taking into account changes in the demographic structure of the population. We identify the most vulnerable groups of this recession by dissagregating the workforce by age, gender and race. We find that adjusting for the aging of the U.S. labor force increases the severity of this recession. Our results indicate that the increase in the unemployment rate is driven to a larger extent by the lack of hiring (low outflows), but flows into unemployment are still important for understanding unemployment rate dynamics (they are not as acyclical as some literature suggests) and differences in unemployment rates across demographic groups. We find that this is indeed a mancession, as men face higher job separation probabilities, lower job finding probabilities and, as a result, higher unemployment rates than women. Lastly, there is some evidence that blacks suffered more than whites (again, this difference is particularly pronounced for men)

The Job Search Intensity Supply Curve: How Labor Market Conditions Affect Job Search Effort

During the Great Recession of 2007, unemployment reached nearly 10 percent and the ratio of unemployment to open positions (as measured by the Help Wanted OnLine Index) more than tripled. The weak labor market prompted an unprecedented extension in the length of time in which a claimant can collect unemployment insurance (UI) to 99 weeks, at an expense to date of $226.4 billion. While many claim that extending UI during a recession will reduce search intensity, the effect of weak labor market conditions on search remains a mystery. As a result, policymakers are in the dark as to whether UI extensions reduce already low search effort during recessions or perhaps decrease excessive search, which causes congestion in the labor market. At the same time, modelers of the labor market have little empirical justification for their assumptions on how search intensity changes over the business cycle. This paper develops a search model where the impact of macro labor market conditions on a worker’s search effort depends on whether these two factors are substitutes or complements in the job search process. Parameter estimates of the structural model using a sample of unemployment spells from the National Longitudinal Survey of Youth 1997 indicate that macro labor market conditions and individual search effort are complements and move together over the business cycle. The estimation also reveals that more risk-averse and less wealthy individuals exhibit less search effort

The Network Composition of Aggregate Unemployment

We develop a theory of unemployment in which workers search for jobs through a network of firms, the labor flow network (LFN). The lack of an edge between two companies indicates the impossibility of labor flows between them due to high frictions. In equilibrium, firms' hiring behavior correlates through the network, modulating labor flows and generating aggregate unemployment. This theory provides new micro-foundations for the aggregate matching function, the Beveridge curve, wage dispersion, and the employer-size premium. Using employer-employee matched records, we study the effect of the LFN topology through a new concept: `firm-specific unemployment'