Classification of Perturbations for Membranes with Bending Rigidity

A complete classification of the renormalization-group flow is given for impurity-like marginal operators of membranes whose elastic stress scales like (\Delta r)^2 around the external critical dimension d_c=2. These operators are classified by characteristic functions on R^2 x R^2.Comment: latex, 3 .eps-file

Large-Scale Loan Portfolio Selection

We consider the problem of optimally selecting a large portfolio of risky loans, such as mortgages, credit cards, auto loans, student loans, or business loans. Examples include loan portfolios held by financial institutions and fixed-income investors as well as pools of loans backing mortgage- and asset-backed securities. The size of these portfolios can range from the thousands to even hundreds of thousands. Optimal portfolio selection requires the solution of a high-dimensional nonlinear integer program and is extremely computationally challenging. For larger portfolios, this optimization problem is intractable. We propose an approximate optimization approach that yields an asymptotically optimal portfolio for a broad class of data-driven models of loan delinquency and prepayment. We prove that the asymptotically optimal portfolio converges to the optimal portfolio as the portfolio size grows large. Numerical case studies using actual loan data demonstrate its computational efficiency. The asymptotically optimal portfolio’s computational cost does not increase with the size of the portfolio. It is typically many orders of magnitude faster than nonlinear integer program solvers while also being highly accurate even for moderate-sized portfolios

Diagnosing shortwave cryosphere radiative effect and its 21st century evolution in CESM

We incorporate a new diagnostic called the cryosphere radiative effect (CrRE), the instantaneous influence of surface snow and sea ice on the top‐of‐model solar energy budget, into two released versions of the Community Earth System Model (CESM1 and CCSM4). CrRE offers a more climatically relevant metric of the cryospheric state than snow and sea ice extent and is influenced by factors such as the seasonal cycle of insolation, cloud masking, and vegetation cover. We evaluate CrRE during the late 20th century and over the 21st century, specifically diagnosing the nature of CrRE contributions from terrestrial and marine sources. The radiative influence of ice sheets and glaciers is not considered, but snow on top of them is accounted for. Present‐day global CrRE in both models is −3.8 W m −2 , with a boreal component (−4.2 to −4.6 W m −2 ) that compares well with observationally derived estimates (−3.9 to −4.6 W m −2 ). Similar present‐day CrRE in the two model versions results from compensating differences in cloud masking and sea ice extent. Over the 21st century, radiative forcing in the Representative Concentration Pathway (RCP) 8.5 scenario causes reduced boreal sea ice cover, austral sea ice cover, and boreal snow cover, which all contribute roughly equally to enhancing global absorbed shortwave radiation by 1.4–1.8 Wm −2 . Twenty‐first century RCP8.5 global cryospheric albedo feedback are +0.41 and +0.45 W/m 2 /K, indicating that the two models exhibit similar temperature‐normalized CrRE change. Key Points We implement the first GCM diagnostic calculation of cryosphere radiative effect Global average CrRE from snow and sea ice is −4 W m −2 in present‐day simulations Earth absorbs 1.6 W m −2 more insolation from cryosphere loss by 2099 in RCP8.5Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106707/1/jgrd51156.pd

Breeding CWG-R crested wheatgrass for reduced-maintenance turf

Using reduced-maintenance turfgrass as an alternative to current high-maintenance turfgrass species would conserve resources, labor, and potentially reduce pollutants in the environment. CWG-R is an experimental population of crested wheatgrass [Agropyron cristatum (L.) Gaertn.] from Iran that has shown potential as a low-maintenance turf. The objective of this research was to estimate the genetic variation for turf traits within the CWG-R population when evaluated under a reduced-maintenance regimen. Ninety CWG-R clonal lines were established in 1998 near Logan, UT, as spaced-plant plots in a RCB design with four replicates. Maintenance of 50% ET0 replacement, 97.74 kg of nitrogen ha1yr1, and mowing at 7.62 cm was approximately 40% lower than typical for high-input Kentucky bluegrass (Poa pratensis L.) turf. Critical turf traits, including spring regrowth, season-long (March–October) and mid-summer (June–July) turf quality, color, and rhizomatous spread were evaluated in 1999 and 2000. Significant genetic variation among clonal lines was evident with broad-sense heritabilities of 0.65, 0.76, 0.45, and 0.76 for spring regrowth, season-long turf quality, color, and rhizomatous spread, respectively. Several clonal lines remained green throughout the summer months and maintained acceptable turf quality and color ratings during the critical mid-summer period. The high broad-sense heritability estimates within this population indicate potential for successful improvement of critical turf traits by phenotypic selection. These results indicate that that CWG-R could be an important low-maintenance turf-type crested wheatgrass germplasm

Super-rough phase of the random-phase sine-Gordon model: Two-loop results

We consider the two-dimensional random-phase sine-Gordon and study the vicinity of its glass transition temperature $T_c$, in an expansion in small $\tau=(T_c-T)/T_c$, where $T$ denotes the temperature. We derive renormalization group equations in cubic order in the anharmonicity, and show that they contain two universal invariants. Using them we obtain that the correlation function in the super-rough phase for temperature $T<T_c$ behaves at large distances as $\bar{} = \mathcal{A}\ln^2(|x|/a) + \mathcal{O}[\ln(|x|/a)]$, where the amplitude $\mathcal{A}$ is a universal function of temperature $\mathcal{A}=2\tau^2-2\tau^3+\mathcal{O}(\tau^4)$. This result differs at two-loop order, i.e., $\mathcal{O}(\tau^3)$, from the prediction based on results from the "nearly conformal" field theory of a related fermion model. We also obtain the correction-to-scaling exponent.Comment: 34 page