Managing a Retirement Portfolio: Do Annuities Provide More Safety?

Even with the generally recognized “safe” withdrawal amount of 4% of the retirement portfolio starting balance, more than 5% of retirement portfolios will run out of money over a 30-year period. Bootstrap simulations were used to estimate the probability of outliving a retirement portfolio as increasing proportions of a tax-deferred account are annuitized. The impacts of Required Minimum Distributions and taxable Social Security income were incorporated into the analysis. Results indicate that annuities significantly extend the length of time the portfolio lasts, but the expected balance remaining (estate size) will decrease substantially, a trade-off of security versus a legacy. Advisors and planners may find the graphical exposition helpful when showing clients different tradeoff options

Retirement Withdrawals: an Analysis of the Benefits of Periodic “Midcourse” Adjustments

Much research has addressed the question of how much money can safely be withdrawn from a retirement portfolio without prematurely running out of money (shortfall risk). Instead of constant (inflation adjusted) annual withdrawals, this study uses withdrawal amounts (and optionally, asset allocations) that are modified every five years over a 30-year withdrawal horizon. A bootstrap is used initially to obtain the conditional probability rules. Further simulations demonstrate that periodic (every five years) adjustments can decrease the risk of running out of money as well as increase the amount withdrawn, as compared to a “constant withdrawal amount” strateg

Shortfall Risk of Target-date Funds During Retirement

Target-date mutual funds are likely to increase in popularity because they are now one of the three approved default options for many retirement plans. In the retirement years, target-date funds become increasingly conservative with higher bond concentrations. Using a bootstrap simulation and rolling period analysis, three target-date fund classifications are shown to have higher probabilities of running out of money and lower balance remaining when compared to fixed allocation portfolios. A fixed 50/50 stock/bond portfolio unambiguously out-performs the target-date funds, regardless of methodology employed. In light of this evidence, these funds should revisit their asset allocation strategy

The Fallacy of Cookie Cutter Asset Allocation: Some Evidence from \u27New York\u27s College Savings Program\u27

In this paper. we establish why \u27\u27prefabricated\u27\u27 asset allocation schemes mandated by some education savings programs might be suboptimal. Then. using the New York\u27s College Savings Program a an example, we simulate and then compare end of period wealth accumulated in both a tax preferred but regimented asset allocation plan, and in a nontax protected plan. We find. first. that the longer the child participates in the plan. the greater the benefit. Second. participants in higher tax brackets derive greater benefits; adherence to prespecified asset allocation for low tax bracket investors often results in return loss that overshadows the tax benefit

Γ to X Transport of Photoexcited Electrons in Type II GaAs/AlAs Multiple Quantum Well Structures

We report novel femtosecond time‐resolved measurements performed on staggered type II GaAs/AlAs multiple quantum well structures. Photoexcited electrons were determined to transfer from the Γ valley of the GaAs layers to the X valleys of the AlAs in 100 and 400 fs for 8‐ and 11‐monolayer‐thick GaAs samples, respectively

Collective traffic-like movement of ants on a trail: dynamical phases and phase transitions

The traffic-like collective movement of ants on a trail can be described by a stochastic cellular automaton model. We have earlier investigated its unusual flow-density relation by using various mean field approximations and computer simulations. In this paper, we study the model following an alternative approach based on the analogy with the zero range process, which is one of the few known exactly solvable stochastic dynamical models. We show that our theory can quantitatively account for the unusual non-monotonic dependence of the average speed of the ants on their density for finite lattices with periodic boundary conditions. Moreover, we argue that the model exhibits a continuous phase transition at the critial density only in a limiting case. Furthermore, we investigate the phase diagram of the model by replacing the periodic boundary conditions by open boundary conditions.Comment: 8 pages, 6 figure

Is Thermal Instability Significant in Turbulent Galactic Gas?

We investigate numerically the role of thermal instability (TI) as a generator of density structures in the interstellar medium (ISM), both by itself and in the context of a globally turbulent medium. Simulations of the instability alone show that the condenstion process which forms a dense phase (``clouds'') is highly dynamical, and that the boundaries of the clouds are accretion shocks, rather than static density discontinuities. The density histograms (PDFs) of these runs exhibit either bimodal shapes or a single peak at low densities plus a slope change at high densities. Final static situations may be established, but the equilibrium is very fragile: small density fluctuations in the warm phase require large variations in the density of the cold phase, probably inducing shocks into the clouds. This result suggests that such configurations are highly unlikely. Simulations including turbulent forcing show that large- scale forcing is incapable of erasing the signature of the TI in the density PDFs, but small-scale, stellar-like forcing causes erasure of the signature of the instability. However, these simulations do not reach stationary regimes, TI driving an ever-increasing star formation rate. Simulations including magnetic fields, self-gravity and the Coriolis force show no significant difference between the PDFs of stable and unstable cases, and reach stationary regimes, suggesting that the combination of the stellar forcing and the extra effective pressure provided by the magnetic field and the Coriolis force overwhelm TI as a density-structure generator in the ISM. We emphasize that a multi-modal temperature PDF is not necessarily an indication of a multi-phase medium, which must contain clearly distinct thermal equilibrium phases.Comment: 18 pages, 11 figures. Submitted to Ap

The magnetic nature of disk accretion onto black holes

Although disk accretion onto compact objects - white dwarfs, neutron stars, and black holes - is central to much of high energy astrophysics, the mechanisms which enable this process have remained observationally elusive. Accretion disks must transfer angular momentum for matter to travel radially inward onto the compact object. Internal viscosity from magnetic processes and disk winds can in principle both transfer angular momentum, but hitherto we lacked evidence that either occurs. Here we report that an X-ray-absorbing wind discovered in an observation of the stellar-mass black hole binary GRO J1655-40 must be powered by a magnetic process that can also drive accretion through the disk. Detailed spectral analysis and modeling of the wind shows that it can only be powered by pressure generated by magnetic viscosity internal to the disk or magnetocentrifugal forces. This result demonstrates that disk accretion onto black holes is a fundamentally magnetic process.Comment: 15 pages, 2 color figures, accepted for publication in Nature. Supplemental materials may be obtained by clicking http://www.astro.lsa.umich.edu/~jonmm/nature1655.p

Gender differences in the association between adiposity and probable major depression: a cross-sectional study of 140,564 UK Biobank participants

<b>Background</b><p></p> Previous studies on the association between adiposity and mood disorder have produced contradictory results, and few have used measurements other than body mass index (BMI). We examined the association between probable major depression and several measurements of adiposity: BMI, waist circumference (WC), waist-hip-ratio (WHR), and body fat percentage (BF%).<p></p> <b>Methods</b><p></p> We conducted a cross-sectional study using baseline data on the sub-group of UK Biobank participants who were assessed for mood disorder. Multivariate logistic regression models were used, adjusting for potential confounders including: demographic and life-style factors, comorbidity and psychotropic medication.<p></p> <b>Results</b><p></p> Of the 140,564 eligible participants, evidence of probable major depression was reported by 30,145 (21.5%). The fully adjusted odds ratios (OR) for obese participants were 1.16 (95% confidence interval (CI) 1.12, 1.20) using BMI, 1.15 (95% CI 1.11, 1.19) using WC, 1.09 (95% CI 1.05, 1.13) using WHR and 1.18 (95% CI 1.12, 1.25) using BF% (all p <0.001). There was a significant interaction between adiposity and gender (p = 0.001). Overweight women were at increased risk of depression with a dose response relationship across the overweight (25.0-29.9 kg/m2), obese I (30.0-34.9 kg/m2), II (35.0-39.9 kg/m2) and III (≥40.0 kg/m2) categories; fully adjusted ORs 1.14, 1.20, 1.29 and 1.48, respectively (all p < 0.001). In contrast, only obese III men had significantly increased risk of depression (OR 1.29, 95% CI 1.08, 1.54, p = 0.006).<p></p> <b>Conclusion</b><p></p> Adiposity was associated with probable major depression, irrespective of the measurement used. The association was stronger in women than men. Physicians managing overweight and obese women should be alert to this increased risk

MetaCyto: A Tool for Automated Meta-analysis of Mass and Flow Cytometry Data

While meta-analysis has demonstrated increased statistical power and more robust estimations in studies, the application of this commonly accepted methodology to cytometry data has been challenging. Different cytometry studies often involve diverse sets of markers. Moreover, the detected values of the same marker are inconsistent between studies due to different experimental designs and cytometer configurations. As a result, the cell subsets identified by existing auto-gating methods cannot be directly compared across studies. We developed MetaCyto for automated meta-analysis of both flow and mass cytometry (CyTOF) data. By combining clustering methods with a silhouette scanning method, MetaCyto is able to identify commonly labeled cell subsets across studies, thus enabling meta-analysis. Applying MetaCyto across a set of ten heterogeneous cytometry studies totaling 2,926 samples enabled us to identify multiple cell populations exhibiting differences in abundance between demographic groups