Impulse approximation in the n p --> d pi^0 reaction reexamined

The impulse approximation (one-body operator) in the n p --> d pi^0 reaction is reexamined with emphasis on the issues of reducibility and recoil corrections. An inconsistency when one pion exchange is included in the production operator is demonstrated and then resolved via the introduction of "wave function corrections" which nearly vanish for static nucleon propagators. Inclusion of the recoil corrections to the nucleon propagators is found to change the magnitude and sign of the impulse production amplitude, worsening agreement with the experimental cross section by approximately 30%. A cutoff is used to account for the phenomenological nature of the external wave functions, and is found to have a significant impact up to approximately 2.5 GeV.Comment: Published versio

WILDFIRES IN THE NORTHEASTERN UNITED STATES: EVALUATING FIRE OCCURRENCE AND RISK IN THE PAST, PRESENT, AND FUTURE

Climate change is one of the most complex and challenging issues facing the world today. A changing climate will affect humankind in many ways and alter our physical environment, presenting ethical challenges in how we respond. The impact of climate change will likely be exacerbated in heavily populated regions of the planet, such as the Northeastern United States (NEUS). The NEUS is comprised of complex, sprawling urban centers and rural regions, both of which are vital to the economic and cultural character of the region. Furthermore, both urban and rural areas in the NEUS contain communities that have been historically susceptible to climate change (Horton et al. 2014). Over the past 120 years, average temperatures have increased by 2°F, precipitation has increased by 10%, and sea levels have also risen (Kunkel 2013). One poorly understood consequence of climate change is its effects on extreme events such as wildfires. Robust associations between wildfire frequency and climatic variability have been shown to exist (Scholze et al. 2006; Westerling et al. 2006), indicating that future climate change may continue to have a significant effect on wildfire activity. The NEUS has been home to some of the most infamous and largest historic “megafires” in North America, such as the Miramichi Fire of 1825 and the fires of 1947 (Irland 2013). Although return intervals in most areas of the NEUS are high (hundreds of years), wildfires have played a critical role in ecosystem development and forest structure in the region (Carlson 2013). Therefore, predicting fire occurrence and vulnerability to large wildfires in the NEUS is economically and culturally relevant. However, predicting fire occurrence is not a simple task due to the nature of wildfire activity in the NEUS. While in most regions of the world, natural factors such as lightning are the driving cause of wildfires, it has been estimated that the vast majority (\u3e99%) of wildfires in the NEUS are caused by anthropogenic activity and not natural causes (Pyne 1982). Consequently, only studying data associated with fire occurrence (i.e. area burned, number of fires) is likely inadequate for the investigation the region’s fire risk over time. Furthermore, little is known about how the direct (temperature & precipitation trends) and indirect (ecosystem-wide species distribution) effects of climate change will impact fire risk in the NEUS under future climate scenarios. Fully understanding the natural mechanisms that control fire risk and occurrence requires continuous records of past fires and climatic variability on centennial to millennial timescales. However, historical fire records in the NEUS are temporally limited, and do not provide an adequate analysis of the impacts of regional wildfire regimes, prior to human disturbance and anthropogenic climate change. We find that regional climatic fire risk for the NEUS can be estimated most accurately using the Keetch Byram Drought Index (KBDI) from 20th century historical meteorological records from various stations located throughout the region. Regional fire risk is then estimated through 2100 AD, using the KBDI and dynamically downscaled regional climate models from CMIP5 climate models. Under RCP 8.5, average KBDI and max yearly KBDI is shown to increase by 300% and 500%, respectively, in an exponential trend. Under RCP 4.5, KBDI is also expected to increase through 2100 AD to a lesser extent. Interestingly, these increases in regional fire risk are present regardless of increases in precipitation, indicating that future fire risk in the NEUS is driven largely by changes in temperature as opposed to precipitation. In order to investigate long-term regional wildfire activity over the past millennium, we examine PAHs and macrocharcoal from a varved sedimentary record from Basin Pond, Fayette, Maine (USA). We find elevated concentrations of the PAH retene were found to be highly correlated with known large-scale regional wildfire events that occurred in 1761-1762, 1825, and 1947 (A.D.). To distinguish between biomass burning and anthropogenic combustion, we examined the ratio of the PAHs retene and chrysene. The new Basin Pond PAH records, along with a local signal of fire occurrence from charcoal analysis, offers the prospect of using this multi-proxy approach as a method for examining wildfire frequency at the local and regional scale in the NEUS. Finally, we report seasonally resolved measurements of brGDGT production in the water column, in catchment soils, and in a sediment core from Basin Pond. We utilize these observations to help interpret a Basin Pond brGDGT-based temperature reconstruction spanning the past 900 years. This record exbibits similar trends to a pollen record from the same site and also to regional and global syntheses of terrestrial temperatures over the last millennium. However, the Basin Pond temperature record shows higher-frequency variability than has previously been captured by such an archive in the NEUS, potentially attributed to large scale atmospheric patterns. These new records of temperature variability and wildfire activity, when compared to regional hydroclimate records, shed insight into pre-historic wildfire risk in the NEUS

A High-Resolution Paleoenvironmental and Paleoclimatic History of Extreme Events on the Laminated Sediment Record from Basin Pond, Fayette, Maine, U.S.A.

Future impacts from climate change can be better understood by placing modern climate trends into perspective through extension of the short instrumental records of climate variability. This is especially true for extreme climatic events, such as extreme precipitation and wildfires, as the period of instrumental records provides only a few examples and these have likely have been influenced by anthropogenic warming. Multi-parameter records showing the past range of climate variability can be obtained from lakes. Lakes are particularly good recorders of climate variability because sediment from the surrounding environment accumulates in lakes, making them sensitive recorders of climate variability and providing high-resolution histories of local environmental conditions in the past. In some cases, such as at Basin Pond, sediment is persevered efficiently enough to produce distinguishable annual laminations (varves) in the sedimentary record. The varved record at Basin Pond was used to construct an accurate, highly-resolved age-to-depth model over the past 300 years. Using a multi-proxy analysis, including organic biomarker analysis of molecular compounds and sedimentological features preserved in the sediment record, a history of environmental and climatic change at Basin Pond was constructed. These analyses were compared with the record of known extreme events (from instrumental measurements and historical documents), including 129 years of high-resolution precipitation and temperature meteorological data, 19 tropical systems over the past 145 years, and two known wildfire events over the past 200 years. Long-term trends in precipitation, including the increase in precipitation seen throughout the last half of the 20th century and the drought of the 1940’s, were captured in the analysis of long-chain n-alkane distributions and through varve thickness measurements obtained through X-Ray Fluorescence analysis. Furthermore, Polycyclic Aromatic Hydrocarbons (PAHs), a class of organic compounds that can be used to trace combustion activity, were found in abundance in the Basin Pond sedimentary record. Peaks in the abundances of two PAHs (retene and chrysene) and the ratio retene/(retene + chrysene) were found to be highly correlated with the known wildfire events occurring in the historical period, giving promise as using these compounds and ratio as a robust proxy for regional wildfire events in the northeastern U.S

Break in the VHE spectrum of PG 1553+113: new upper limit on its redshift?

PG 1553+113 is a known BL Lac object, newly detected in the GeV-TeV energy range by H.E.S.S and MAGIC. The redshift of this source is unknown and a lower limit of $z > 0.09$ was recently estimated. The very high energy (VHE) spectrum of PG 1553+113 is attenuated due to the absorption by the low energy photon field of the extragalactic background light (EBL). Here we correct the combined H.E.S.S and MAGIC spectrum of PG 1553+113 for this absorption assuming a minimum density of the evolving EBL. We use an argument that the intrinsic photon index cannot be harder than $\Gamma = 1.5$ and derive an upper limit on the redshift of $z < 0.69$. Moreover, we find that a redshift above $z = 0.42$ implies a possible break of the intrinsic spectrum at about 200 GeV. Assuming that such a break is absent, we derive a much stronger upper limit of $z < 0.42$. Alternatively, this break might be attributed to an additional emission component in the jet of PG 1553+113. This would be the first evidence for a second component is detected in the VHE spectrum of a blazar.Comment: revised version submitted to Ap

2-D Compass Codes

The compass model on a square lattice provides a natural template for building subsystem stabilizer codes. The surface code and the Bacon-Shor code represent two extremes of possible codes depending on how many gauge qubits are fixed. We explore threshold behavior in this broad class of local codes by trading locality for asymmetry and gauge degrees of freedom for stabilizer syndrome information. We analyze these codes with asymmetric and spatially inhomogeneous Pauli noise in the code capacity and phenomenological models. In these idealized settings, we observe considerably higher thresholds against asymmetric noise. At the circuit level, these codes inherit the bare-ancilla fault-tolerance of the Bacon-Shor code.Comment: 10 pages, 7 figures, added discussion on fault-toleranc

Synchronization of dynamical hypernetworks: dimensionality reduction through simultaneous block-diagonalization of matrices

We present a general framework to study stability of the synchronous solution for a hypernetwork of coupled dynamical systems. We are able to reduce the dimensionality of the problem by using simultaneous block-diagonalization of matrices. We obtain necessary and sufficient conditions for stability of the synchronous solution in terms of a set of lower-dimensional problems and test the predictions of our low-dimensional analysis through numerical simulations. Under certain conditions, this technique may yield a substantial reduction of the dimensionality of the problem. For example, for a class of dynamical hypernetworks analyzed in the paper, we discover that arbitrarily large networks can be reduced to a collection of subsystems of dimensionality no more than 2. We apply our reduction techique to a number of different examples, including a class of undirected unweighted hypermotifs of three nodes.Comment: 9 pages, 6 figures, accepted for publication in Phys. Rev.

TECHNIQUES TO FACILITATE REDUNDANCY FOR DYNAMIC TELEMETRY SUBSCRIPTIONS IN A NETWORK ENVIRONMENT

Network administrators often desire redundancy when creating telemetry subscriptions in order to ensure that updates are not lost if a particular receiver fails. However, dynamic telemetry subscriptions do not offer a natural way to achieve such a redundancy. Proposed herein are techniques to facilitate redundancy for dynamic telemetry subscriptions through which multiple telemetry data receivers, that each initiate a dynamic telemetry subscription Remote Procedure Call (RPC) towards a device, can be attached to an existing subscription initiated by a first receiver as long as parameters for the subscription RPCs initiated by the receivers are identical to parameters for the existing subscription initiated by the first receiver. Such techniques can be utilized to reduce duplication in collecting data from a backend and also to enable higher scaling

Emerging Investigators Series: Pyrolysis Removes Common Microconstituents Triclocarban, Triclosan, and Nonylphenol from Biosolids

Reusing biosolids is vital for the sustainability of wastewater management. Pyrolysis is an anoxic thermal degradation process that can be used to convert biosolids into energy rich py-gas and py-oil, and a beneficial soil amendment, biochar. Batch biosolids pyrolysis (60 minutes) revealed that triclocarban and triclosan were removed (to below quantification limit) at 200 °C and 300 °C, respectively. Substantial removal (\u3e90%) of nonylphenol was achieved at 300 °C as well, but 600 °C was required to remove nonylphenol to below the quantification limit. At 500 °C, the pyrolysis reaction time to remove \u3e90% of microconstituents was less than 5 minutes. Fate studies revealed that microconstituents were both volatilized and thermochemically transformed during pyrolysis; microconstituents with higher vapor pressures were more likely to volatilize and leave the pyrolysis reactor before being transformed than compounds with lower vapor pressures. Reductive dehalogenation products of triclocarban and suspected dehalogenation products of triclosan were identified in py-gas. Application of biosolids-derived biochar to soil in place of biosolids has potential to minimize organic microconstituents discharged to the environment provided appropriate management of py-gas and py-oil