Entropy and Correlations in Lattice Gas Automata without Detailed Balance

We consider lattice gas automata where the lack of semi-detailed balance results from node occupation redistribution ruled by distant configurations; such models with nonlocal interactions are interesting because they exhibit non-ideal gas properties and can undergo phase transitions. For this class of automata, mean-field theory provides a correct evaluation of properties such as compressibility and viscosity (away from the phase transition), despite the fact that no H-theorem strictly holds. We introduce the notion of locality - necessary to define quantities accessible to measurements - by treating the coupling between nonlocal bits as a perturbation. Then if we define operationally ``local'' states of the automaton - whether the system is in a homogeneous or in an inhomogeneous state - we can compute an estimator of the entropy and measure the local channel occupation correlations. These considerations are applied to a simple model with nonlocal interactions.Comment: 13 pages, LaTeX, 5 PostScript figures, uses psfig. Submitted to Int. J. Mod. Phys.

The Impact of Pensions on State Borrowing Costs

Municipal bond prices are tumbling and rates rising just as public borrowers face pressure to refinance deals cut during the financial crisis. At the same time, the funded status of public pension plans has declined, and states and localities will have to come up with more money to meet future benefit payments. In the private sector, numerous studies have shown that pension underfunding affects corporate bond ratings. And Moody’s just announced that it would combine unfunded pension liabilities with outstanding bonds when evaluating a state’s leverage position. These developments raise the question of how future pension commitments affect today’s borrowing costs in the public sector. The brief proceeds as follows. The first section describes the municipal bond market. The second section describes the factors that traditionally have been considered in the bond rating process. The third section summarizes what other researchers have found regarding the relationship between pension commitments and borrowing costs in the private and public sectors. The fourth section presents a model for the period 2005-2009 that relates borrowing costs to factors generally considered by the rating agencies, such as the state’s management, finances, economy, and debt structure. Pensions are a component of the debt structure, and the extent to which states make their Annual Required Contribution (ARC) has a statistically significant – albeit modest – impact on the cost of debt. A side finding is that the bond’s rating explains relatively little about the variation in interest cost, and the effect of pensions remains significant even including the bond’s rating in the equation. The final section concludes that while pension underfunding had only a small effect on borrowing costs in the 2005-2009 period when pension expenses were only 3 to 4 percent of state budgets, its impact could become more significant as the cost of pensions increases.

The Impact of Public Pensions on State and Local Budgets

State and local pensions have been headline news since the financial collapse reduced the value of their assets, leaving a substantial unfunded liability. The magnitude of that liability depends on the interest rate used to discount future benefit promises but, regardless of the assumptions, states and localities are going to have to come up with more money. This brief looks at the size of the additional funding relative to state budgets. The brief proceeds as follows. The first section provides an overview of state and local plans and in­troduces our sample of six states: California, Florida, Georgia, Illinois, Massachusetts, and New Jersey. The second section presents data on pension expendi­tures relative to budget totals for states and localities in the aggregate and for our sample of plans. The third section develops baseline budgets for the period 2010-2043 for all states and localities and for the six individual states. It then projects annual required pension contributions beginning in 2014 under three scenarios: 1) amortizing the unfunded liability valued at an 8-percent discount rate over the next 30 years; 2) amortizing the unfunded liability valued at 5 per­cent over the next 30 years; and 3) continuing to pay contributions at current levels until the trust fund is exhausted and then paying benefits on a pay-as-you-go basis. The final section concludes that whereas public plans are substantially underfunded, in the aggregate they currently account for only 3.8 percent of state and local spending. Assuming 30-year amortization beginning in 2014, this share would rise to only 5.0 percent and, even assuming a 5-percent discount rate, to only 9.1 percent. Aggregate data, however, hide substantial variation. States that have seriously underfunded plans and/or generous benefits, such as California, Illinois, and New Jersey, would see contributions rise to about 8 percent of budgets with an 8-percent discount rate and 12.5 percent with a 5-percent discount rate.State and Local Pensions

A Role for Defined Contribution Plans in the Public Sector

In the wake of the financial crisis, policymakers have been talking about shifting from defined benefit plans to defined contribution plans in the public sector. Three states – Georgia, Michigan, and Utah – have taken action, joining the 10 states that had introduced some form of defined contribution plans before 2008. Interestingly, these new plans are “hybrids” that combine elements of both defined benefit plans and defined contribution plans. Such an approach spreads the risks associated with the provision of retirement income between the employer and the employee. This brief provides an update on defined contribution initiatives in the public sector and then discusses whether the hybrids that have been introduced are the best way to combine the two plan types. The brief proceeds as follows. The first section discusses the issues involved with moving from a defined benefit plan to a defined contribution arrangement. The second section recaps the role that defined contribution plans played in the public sector before the financial crisis. The third section describes the new hybrid plans recently adopted in Georgia, Michigan, and Utah. And the fourth section suggests that a better type of hybrid might be one where defined contribution plans are “stacked” on the state’s defined benefit plan rather than placed alongside of it. The fifth section concludes that defined contribution plans have a role in the public sector, but that role is supplementing, not replacing, defined benefit plans.

How Prepared Are State and Local Workers for Retirement

A widespread perception is that state-local government workers receive high pension benefits which, combined with Social Security, provide more than adequate retirement income. The perception is consistent with multiplying the 2-percent benefit factor in most plan formulae by a 35- to 40- year career and adding a Social Security benefit. But this calculation assumes that individuals spend enough of their career in the public sector to produce such a retirement outcome. This brief summarizes the results of a paper that uses Health and Retirement Study (HRS) and actuarial reports published by state and local pension systems to test the hypothesis that state-local workers have more than enough money for retirement.

Oscillations and translation of a free cylinder in a confined flow

An oscillatory instability has been observed experimentally on an horizontal cylinder free to move and rotate between two parallel vertical walls of distance H; its characteristics differ both from vortex shedding driven oscillations and from those of tethered cylinders in the same geometry. The vertical motion of the cylinder, its rotation about its axis and its transverse motion across the gap have been investigated as a function of its diameter D, its density s, of the mean vertical velocity U of the fluid and of its viscosity. For a blockage ratio D/H above 0.5 and a Reynolds number Re larger then 14, oscillations of the rolling angle of the cylinder about its axis and of its transverse coordinate in the gap are observed together with periodic variations of the vertical velocity. Their frequency f is the same for the sedimentation of the cylinder in a static fluid (U = 0) and for a non-zero mean flow (U 6= 0). The Strouhal number St associated to the oscillation varies as 1/Re with : St.Re = 3 $\pm$ 0.15. The corresponding period 1/f is then independent of U and corresponds to a characteristic viscous diffusion time over a distance ~ D, implying a strong influence of the viscosity. These characteristics differ from those of vortex shedding and tethered cylinders for which St is instead roughly constant with Re and higher than here

Can State and Local Pensions Muddle Through?

The finances of state and local pension plans are headline news almost daily.1 Indeed, although these plans were moving toward prefunding their promised benefits, two financial crises in 10 years have thrown them seriously off course. Measured by the standards of the Government Accounting Standards Board, between 2008 and 2009 the ratio of assets to liabilities for our sample of 126 plans dropped from 84 percent to 79 percent. But this decline is only the beginning of the bad news that will emerge as the losses are spread over the next several years. Furthermore, the funded levels are closer to 50 percent if liabilities are discounted by a riskless rate, as recommended by economists and financial experts.2 What do these numbers imply for the future of these plans? Here’s what’s happening. States and localities have increased contributions and extended retirement ages for new employees, but these changes will take a long time to have any substantial effect. In most states, constitutional protections and court rulings have prohibited public employers from cutting benefits for existing employees. Thus, the only option for a quick fix would be an infusion of tax revenues. But the recession has decimated tax revenues and increased the demand for state and local services. Thus, the question is whether these plans have enough assets to muddle along until the economy and the stock market recover. Or do they face a liquidity crisis? That is the subject of this brief. The discussion is as follows. The first section looks at the simple ratio of assets to benefits over time and across plans in 2009. The second section moves to a more dynamic approach and investigates two concepts for estimating when plans would run out of money. Under a “termination” concept, where benefits earned to date and plan assets are put in an “old” plan and normal cost payments cover all future accruals, most plans have enough assets to last for at least 15 years. Under a more realistic “ongoing” framework, where normal costs are used to cover benefit payments, most plans have enough for at least 30 years.

The Rotation Measure and 3.5mm Polarization of Sgr A*

We report the detection of variable linear polarization from Sgr A* at a wavelength of 3.5mm, the longest wavelength yet at which a detection has been made. The mean polarization is 2.1 +/- 0.1% at a position angle of 16 +/- 2 deg with rms scatters of 0.4% and 9 deg over the five epochs. We also detect polarization variability on a timescale of days. Combined with previous detections over the range 150-400GHz (750-2000 microns), the average polarization position angles are all found to be consistent with a rotation measure of -4.4 +/- 0.3 x 10^5 rad/m^2. This implies that the Faraday rotation occurs external to the polarized source at all wavelengths. This implies an accretion rate ~0.2 - 4 x 10^-8 Msun/yr for the accretion density profiles expected of ADAF, jet and CDAF models and assuming that the region at which electrons in the accretion flow become relativistic is within 10 R_S. The inferred accretion rate is inconsistent with ADAF/Bondi accretion. The stability of the mean polarization position angle between disparate polarization observations over the frequency range limits fluctuations in the accretion rate to less than 5%. The flat frequency dependence of the inter-day polarization position angle variations also makes them difficult to attribute to rotation measure fluctuations, and suggests that both the magnitude and position angle variations are intrinsic to the emission.Comment: Ap.J.Lett. accepte

A Multidisciplinary Study of the Tongerlo Last Supper and its Attribution to Leonardo Da Vinci’s Second Milanese Studio

This article presents the findings from a two-year study of the Last Supper canvas in the Abbey of Tongerlo, Belgium, including a detailed review of its provenance as well as a multispectral study conducted by IMEC and IPARC. The study used a composite multidisciplinary approach, with traditional connoisseurship and literary research augmented by scientific examination, including IRR (Infrared Reflectography). The article argues that based on the available evidence, the Tongerlo Last Supper was produced in Leonardo’s Milanese workshop between 1507 and 1509, as a collaborative project involving the Leonardeschi Giampietrino, Andrea Solario, and Marco d’Oggiono under Leonardo’s supervision. Furthermore, the infrared spectography scans suggest that the face of John in the painting was painted by Leonardo himself.Questo articolo presenta i risultati di uno studio durato due anni della tela raffigurante l'Ultima Cena nell'Abbazia di Tongerlo, in Belgio. Vi è cui una revisione dettagliata della sua provenienza e uno studio multispettrale condotto da IMEC e IPARC. Lo studio ha utilizzato un approccio multidisciplinare, in cui conoscenza tradizionale e ricerca letteraria sono integrate dall'esame scientifico, in particolare dall'IRR (Riflettografia a infrarossi). Nell'articolo si sostiene che, sulla base delle prove disponibili, l'Ultima Cena di Tongerlo fu prodotta nella bottega milanese di Leonardo tra il 1507 e il 1509, come progetto collaborativo che coinvolse Leonardeschi Giampietrino, Andrea Solario e Marco d'Oggiono sotto la supervisione di Leonardo. Le scansioni effettuate con spettrografia a infrarossi, inoltre, suggeriscono che il volto di Giovanni nel dipinto sia stato dipinto da Leonardo stesso