arXiv subjects

M. Kelley

Publications and source records attributed to M. Kelley.

10 recordsLinked to original sources

arXiv2024

Vertex Imaging Hadron Calorimetry Using AI/ML Tools

The fluctuations in energy loss to processes that do not generate measurable signals, such as binding energy losses, set the limit on achievable hadronic energy resolution in traditional energy reconstruction techniques. The correlation between the number of hadronic interaction vertices in a shower and invisible energy is found to be strong and is used to estimate invisible energy fraction in highly granular calorimeters in short time intervals (<10 ns). We simulated images of hadronic showers using GEANT4 and deployed a neural network to analyze the images for energy regression. The neural network-based approach results in significant improvement in energy resolution, from 13 % to 4 % in the case of a Cherenkov calorimeter for 100 GeV pion showers. We discuss the significance of the phenomena responsible for this improvement and the plans for experimental verification of these results and further development.

physics.ins-det↗

arXiv2024

High-granularity Dual-readout Calorimeter: Evolution of a Classic Prototype

The original dual-readout calorimeter prototype (DREAM), constructed two decades ago, has proven instrumental in advancing our understanding of calorimetry. It has facilitated a multitude of breakthroughs by leveraging signals from complementary media (Cherenkov and scintillation) to capture fluctuations in electromagnetic energy fraction within hadronic showers. Over the years, extensive studies have shed light on the performance characteristics of this module, rendering it exceptionally well-understood. Drawing on this wealth of experience, we have embarked on enhancing the detectors' capabilities further by integrating fast silicon photomultipliers (SiPMs) with finer transverse segmentation, $\sim$1 cm$^2$, as well as longitudinal segmentation by timing measuring better than 10 cm. This configuration will allow us to image hadronic showers with high granularity (HG-DREAM). We argue that the spatial information provided by such a granular detector in a short time window ($\approx$5 ns) leads to substantial enhancement in energy resolution when advanced neural networks are employed in energy reconstruction. We briefly present the current status of work, new concepts that have been introduced to the detector, and expectations from simulations.

physics.ins-det↗

arXiv2020

Nb3Sn multicell cavity coating system at JLAB

SRF niobium cavities are the building blocks of modern accelerators for scientific applications. Lower surface resistance, higher fields, and high operating temperatures advance the reach of the future accelerators for scientific discovery as well as potentially enabling cost-effective industrial solutions. We describe the design and performance of an Nb$_{3}$Sn coating system that converts the inner surface of niobium cavities to Nb$_{3}$Sn film. Niobium surface, heated by radiation from the niobium retort, is exposed to Sn and SnCl$_{2}$ vapor during the heat cycle, which results in about 2 $μ$m Nb$_{3}$Sn film on the niobium surface. Film composition and structure as well as RF properties with 1-cell R\&D cavities and 5-cell practical accelerator cavities are presented.

physics.acc-ph↗

arXiv2018

Climates of Warm Earth-like Planets I: 3-D Model Simulations

We present a large ensemble of simulations of an Earth-like world with increasing insolation and rotation rate. Unlike previous work utilizing idealized aquaplanet configurations we focus our simulations on modern Earth-like topography. The orbital period is the same as modern Earth, but with zero obliquity and eccentricity. The atmosphere is 1 bar N$_{2}$-dominated with CO$_{2}$=400 ppmv and CH$_{4}$=1 ppmv. The simulations include two types of oceans; one without ocean heat transport (OHT) between grid cells as has been commonly used in the exoplanet literature, while the other is a fully coupled dynamic bathtub type ocean. The dynamical regime transitions that occur as day length increases induce climate feedbacks producing cooler temperatures, first via the reduction of water vapor with increasing rotation period despite decreasing shortwave cooling by clouds, and then via decreasing water vapor and increasing shortwave cloud cooling, except at the highest insolations. Simulations without OHT are more sensitive to insolation changes for fast rotations while slower rotations are relatively insensitive to ocean choice. OHT runs with faster rotations tend to be similar with gyres transporting heat poleward making them warmer than those without OHT. For slower rotations OHT is directed equator-ward and no high latitude gyres are apparent. Uncertainties in cloud parameterization preclude a precise determination of habitability but do not affect robust aspects of exoplanet climate sensitivity. This is the first paper in a series that will investigate aspects of habitability in the simulations presented herein. The datasets from this study are opensource and publicly available.

astro-ph.EP↗

arXiv2018

NELIOTA: The wide-field, high-cadence lunar monitoring system at the prime focus of the Kryoneri telescope

We present the technical specifications and first results of the ESA-funded, lunar monitoring project "NELIOTA" (NEO Lunar Impacts and Optical TrAnsients) at the National Observatory of Athens, which aims to determine the size-frequency distribution of small Near-Earth Objects (NEOs) via detection of impact flashes on the surface of the Moon. For the purposes of this project a twin camera instrument was specially designed and installed at the 1.2 m Kryoneri telescope utilizing the fast-frame capabilities of scientific Complementary Metal-Oxide Semiconductor detectors (sCMOS). The system provides a wide field-of-view (17.0' $\times$ 14.4') and simultaneous observations in two photometric bands (R and I), reaching limiting magnitudes of 18.7 mag in 10 sec in both bands at a 2.5 signal-to-noise level. This makes it a unique instrument that can be used for the detection of NEO impacts on the Moon, as well as for any astronomy projects that demand high-cadence multicolor observations. The wide field-of-view ensures that a large portion of the Moon is observed, while the simultaneous, high-cadence, monitoring in two photometric bands makes possible, for the first time, the determination of the temperatures of the impacts on the Moon's surface and the validation of the impact flashes from a single site. Considering the varying background level on the Moon's surface we demonstrate that the NELIOTA system can detect NEO impact flashes at a 2.5 signal-to-noise level of ~12.4 mag in the I-band and R-band for observations made at low lunar phases ~0.1. We report 31 NEO impact flashes detected during the first year of the NELIOTA campaign. The faintest flash was at 11.24 mag in the R-band (about two magnitudes fainter than ever observed before) at lunar phase 0.32. Our observations suggest a detection rate of $1.96 \times 10^{-7}$ events $km^{-2} h^{-1}$.

astro-ph.IM↗

arXiv2016

Exploring the Inner Edge of the Habitable Zone with Fully Coupled Oceans

Rotation in planetary atmospheres plays an important role in regulating atmospheric and oceanic heat flow, cloud formation and precipitation. Using the Goddard Institute for Space Studies (GISS) three dimension General Circulation Model (3D-GCM) we investigate how the effects of varying rotation rate and increasing the incident stellar flux on a planet set bounds on a planet's habitable zone with its parent star. From ensemble climate simulations we identify which factors are the primary controllers of uncertainty in setting these bounds. This is shown in particular for fully coupled ocean (FCO) runs -- some of the first that have been utilized in this context. Results with a Slab Ocean (SO) of 100m mixed layer depth are compared with a similar study by Yang et al. 2014, which demonstrates consistency across models. However, there are clear differences for rotations rates of 1-16x present Earth sidereal day lengths between the 100m SO and FCO models, which points to the necessity of using FCOs whenever possible. The latter was recently demonstrated quite clearly by Hu & Yang 2014 in their aquaworld study with a FCO when compared with similar mixed layer ocean studies and by Cullum et al. 2014. We also show how these results have implications for Venus in the early history of our Solar System since even at this time Venus received more solar flux than Earth does today while it may still have had a slow retrograde rotation. The Venus runs utilize a 2.9Gya solar spectrum generated with the code of Claire et al. 2012, a modern Venus topography with an ocean filling the lowlands (giving an equivalent depth of 310 meters if spread across the entire surface), atmosphere of 1 bar N2, CO2=0.4mb, CH4=0.001mb and present day orbital parameters, radius, & gravity. We demonstrate that ancient Venus could have had quite moderate surface temperatures given these assumptions.

astro-ph.EP↗

arXiv2009

Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington

Context. Near-Earth asteroid-comet transition object 107P/ (4015) Wilson-Harrington is a possible target of the joint European Space Agency (ESA) and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return mission. Physical studies of this object are relevant to this mission, and also to understanding its asteroidal or cometary nature. Aims. Our aim is to obtain significant new constraints on the surface thermal properties of this object. Methods. We present mid-infrared photometry in two filters (16 and 22 microns) obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results from the application of the Near Earth Asteroid Thermal Model (NEATM).We obtained high S/N in two mid-IR bands allowing accurate measurements of its thermal emission. Results. We obtain a well constrained beaming parameter (eta = 1.39 +/- 0.26) and obtain a diameter and geometric albedo of D = 3.46 +/- 0.32 km, and pV = 0.059 +/- 0.011. We also obtain similar results when we apply this best-fitting thermal model to single-band mid-IR photometry reported by Campins et al. (1995), Kraemer et al. (2005) and Reach et al. (2007). Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough lower limit for the thermal inertia of W-H of 60 Jm^-2s^(-0.5)K^-1 when it is at r=1AU, which is slightly over the limit of 30 Jm^-2s^(-0.5)K-1 derived by Groussin et al. (2009) for the thermal inertia of the nucleus of comet 22P/Kopff.

astro-ph.EP↗

arXiv2009

Spitzer Observations of Spacecraft Target 162173 (1999 JU3)

Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Hayabusa-2 sample return mission, and a potential target of the Marco Polo sample return mission. Earth-based studies of this object are fundamental to these missions. We present a mid-infrared spectrum (5-38 microns) of 1999 JU3 obtained with NASA's Spitzer Space Telescope in May 2008. These observations place new constraints on the surface properties of this asteroid. To fit our spectrum we used the near-Earth asteroid thermal model (NEATM) and the more complex thermophysical model (TPM). However, the position of the spin-pole, which is uncertain, is a crucial input parameter for constraining the thermal inertia with the TPM; hence, we consider two pole orientations. In the extreme case of an equatorial retrograde geometry we derive a lower limit to the thermal inertia of 150 J/m^2/K/s^0.5. If we adopt the pole orientation of Abe et al. (2008a) our best-fit thermal model yields a value for the thermal inertia of 700+/-200 J/m^2/K/s^0.5 and even higher values are allowed by the uncertainty in the spectral shape due to the absolute flux calibration. The lower limit to the thermal inertia, which is unlikely but possible, would be consistent with a fine regolith similar to wthat is found for asteroid 433 Eros. However, the thermal inertia is expected to be higher, possibly similar to or greater than that on asteroid 25143 Itokawa. Accurately determining the spin-pole of asteroid 162173 will narrow the range of possible values for its thermal inertia.

astro-ph.EP↗

arXiv2007

Climate simulations for 1880-2003 with GISS modelE

We carry out climate simulations for 1880-2003 with GISS modelE driven by ten measured or estimated climate forcings. An ensemble of climate model runs is carried out for each forcing acting individually and for all forcing mechanisms acting together. We compare side-by-side simulated climate change for each forcing, all forcings, observations, unforced variability among model ensemble members, and, if available, observed variability. Discrepancies between observations and simulations with all forcings are due to model deficiencies, inaccurate or incomplete forcings, and imperfect observations. Although there are notable discrepancies between model and observations, the fidelity is sufficient to encourage use of the model for simulations of future climate change. By using a fixed well-documented model and accurately defining the 1880-2003 forcings, we aim to provide a benchmark against which the effect of improvements in the model, climate forcings, and observations can be tested. Principal model deficiencies include unrealistically weak tropical El Nino-like variability and a poor distribution of sea ice, with too much sea ice in the Northern Hemisphere and too little in the Southern Hemisphere. The greatest uncertainties in the forcings are the temporal and spatial variations of anthropogenic aerosols and their indirect effects on clouds.

physics.ao-ph↗

arXiv2006

Dangerous human-made interference with climate: A GISS modelE study

We investigate the issue of "dangerous human-made interference with climate" using simulations with GISS modelE driven by measured or estimated forcings for 1880-2003 and extended to 2100 for IPCC greenhouse gas scenarios as well as the 'alternative' scenario of Hansen and Sato. Identification of 'dangerous' effects is partly subjective, but we find evidence that added global warming of more than 1 degree C above the level in 2000 has effects that may be highly disruptive. The alternative scenario, with peak added forcing ~1.5 W/m2 in 2100, keeps further global warming under 1 degree C if climate sensitivity is \~3 degrees C or less for doubled CO2. We discuss three specific sub-global topics: Arctic climate change, tropical storm intensification, and ice sheet stability. Growth of non-CO2 forcings has slowed in recent years, but CO2 emissions are now surging well above the alternative scenario. Prompt actions to slow CO2 emissions and decrease non-CO2 forcings are needed to achieve the low forcing of the alternative scenario.

physics.ao-ph↗