ALBERT

Description: Author(s): Youngkuk Kim, C. L. Kane, E. J. Mele, and Andrew M. Rappe Topological crystalline insulators (TCIs) are insulating materials whose topological property relies on generic crystalline symmetries. Based on first-principles calculations, we study a three-dimensional (3D) crystal constructed by stacking two-dimensional TCI layers. Depending on the interlayer in… [Phys. Rev. Lett. 115, 086802] Published Thu Aug 20, 2015

Description: Author(s): Olaf Stenull, C. L. Kane, and T. C. Lubensky Topological mechanics and phononics have recently emerged as an exciting field of study. Here we introduce and study generalizations of the three-dimensional pyrochlore lattice that have topologically protected edge states and Weyl lines in their bulk phonon spectra, which lead to zero surface modes… [Phys. Rev. Lett. 117, 068001] Published Fri Aug 05, 2016

Description: We evaluate local differences in thermal regimes and turbulent heat fluxes across the heterogeneous canopy of a black spruce boreal forest on discontinuous permafrost in interior Alaska. The data were taken during an intensive observing period in the summer of 2013 from two micrometeorological towers 600 m apart in a central section of boreal forest, one in a denser canopy (DC) and the other in a sparser canopy (SC), but under approximately similar atmospheric boundary layer (ABL) flow conditions. Results suggest that on average 34 % of the half-hour periods in a day are non-stationary, primarily during night and during ABL transitions. Also, thermal regimes differ between the two towers; specifically between midnight and 0500 AKST it is about 3 °C warmer at DC. On average, the sensible heat flux at DC was greater. For midday periods, the difference between those fluxes exceeded 30 % of the measured flux and over 30 Wm −2 in magnitude more than 60 % of the time. These differences are due to higher mechanical mixing as a result of the increased density of roughness elements at DC. Finally, the vertical distribution of turbulent heat fluxes verifies a maximum atop the canopy crown (2.6 h) when compared with the sub-canopy (0.6 h) and above canopy (5.1 h), where h is the mean canopy height. We argue that these spatial and vertical variations of sensible heat fluxes result from the complex scale aggregation of energy fluxes over a heterogeneous canopy.

Description: Author(s): Gordon L. Kane, Piyush Kumar, Brent D. Nelson, and Bob Zheng We perform a comprehensive study of models of dark matter (DM) in a Universe with a nonthermal cosmological history, i.e. with a phase of pressureless matter domination before the onset of big-bang nucleosynthesis (BBN). Such cosmological histories are generically predicted by UV completions that co… [Phys. Rev. D 93, 063527] Published Tue Mar 29, 2016

Description: Author(s): Youngkuk Kim, Benjamin J. Wieder, C. L. Kane, and Andrew M. Rappe We propose and characterize a new Z 2 class of topological semimetals with a vanishing spin-orbit interaction. The proposed topological semimetals are characterized by the presence of bulk one-dimensional (1D) Dirac line nodes (DLNs) and two-dimensional (2D) nearly flat surface states, protected by i… [Phys. Rev. Lett. 115, 036806] Published Fri Jul 17, 2015

Description: Author(s): S. M. Young, S. Zaheer, J. C. Y. Teo, C. L. Kane, E. J. Mele, and A. M. Rappe We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protect... [Phys. Rev. Lett. 108, 140405] Published Fri Apr 06, 2012

Description: [1]  Theoretical modeling of strike-slip ruptures along a bimaterial interface suggests that earthquakes initiating on the interface will have a preferred rupture direction. We test this model with 450 small earthquakes (2 〈  M  〈 5) from Parkfield, California, to look for evidence of consistent rupture directivity along the San Andreas Fault. We analyze azimuthal variations in earthquake source spectra after applying an iterative correction for wave propagation effects. Our approach avoids directly modeling source spectra because these models generally assume symmetric rupture; instead, we look for azimuthal variations in the amplitudes of the source spectra over specified frequency bands. Our overall results show similar proportions of events exhibiting characteristics of rupture directivity toward either the southeast or northwest. However, the proportion of events with southeast rupture directivity increases as we limit the data set to larger magnitudes, with 70% of the 46 events M  〉 3 exhibiting southeast rupture characteristics. Some spatial and temporal variability in rupture directivity is also apparent. We observe a higher proportion of northwest directivity ruptures following the 2004  M 6 Parkfield earthquake, which ruptured toward the northwest. Our results are generally consistent with the preferred southeast rupture directivity model but suggest that directivity is likely due to several contributing factors.

Description: Author(s): Steve M. Young and Charles L. Kane Theorists identify two-dimensional crystal structures that could host Dirac electrons similar to those observed in graphene. [Phys. Rev. Lett. 115, 126803] Published Wed Sep 16, 2015

Description: ABSTRACT In this study, long-term discharge data and climate records, such as temperature and precipitation during 1977–2006, have been used to define basin climatic and hydrologic regimes and changes. Discharge analyses at four key gauging stations (Eagle, Stevens Village, Nenana and Pilot stations) in the Yukon River Basin show that the runoff in the cold season (November to April) is low with small variations; while it is high (28,500 to 177,000 ft 3 /s; 810 to 5000 m 3 /s) with high fluctuations in the warm season (May to October). The Stevens Village Station is in the upper basin and has similar changes with the flow near basin outlet. Flow increases in May (61,074 ft 3 /s; 1729 m 3 /s) and September (23,325 ft 3 /s; 660 m 3 /s); and decreases in July (35,174 ft 3 /s; 996 m 3 /s) and August (6,809 ft 3 /s; 193 m 3 /s). Discharge in May at the Pilot Station (near the basin outlet) shows a positive trend (177,000 ft 3 /s; 5010 m 3 /s). Daily flow analyses show high fluctuation during the warm season and very low flow during the cold season; the ten-year average analyses of daily flow at Pilot Station show a small increase in the peak and its timing shifted to a little earlier date. The annual flow, average of 227,900 ft 3 /s (6450 m 3 /s) with high interannual fluctuations, has increased by 18,200 ft 3 /s (or 8%; 520 m 3 /s) during 1977–2006. From 1977 to 2006, basin temperature in June has increased by 3.9 °F (2.2 °C) and decreased by 10.5 °F (5.8 °C) in January. A strong and positive correlation exists between air temperature in April and discharge in May; while a strong and negative correlation relates August temperature and September discharge. Negative trend during 1977–2006 is observed for precipitation in June (0.6 in; 15 mm) with a confidence over 93%. Precipitation in August and September has strong and positive correlations with discharge in September and October at basin outlet; the precipitation in other months has weak correlation with the discharge. The mean annual precipitation during 1977–2006 increased by 1.1 in (or 8%; 28 mm), which contributes to the annual flow increase during the study period. Copyright © 2012 John Wiley & Sons, Ltd.

Description: ABSTRACT In this study, long-term discharge data and climate records, such as temperature and precipitation during 1977–2006, have been used to define basin climatic and hydrologic regimes and changes. Discharge analyses at four key gauging stations (Eagle, Stevens Village, Nenana and Pilot stations) in the Yukon River Basin show that the runoff in the cold season (November to April) is low with small variations; while it is high (28,500 to 177,000 ft 3 /s; 810 to 5000 m 3 /s) with high fluctuations in the warm season (May to October). The Stevens Village Station is in the upper basin and has similar changes with the flow near basin outlet. Flow increases in May (61,074 ft 3 /s; 1729 m 3 /s) and September (23,325 ft 3 /s; 660 m 3 /s); and decreases in July (35,174 ft 3 /s; 996 m 3 /s) and August (6,809 ft 3 /s; 193 m 3 /s). Discharge in May at the Pilot Station (near the basin outlet) shows a positive trend (177,000 ft 3 /s; 5010 m 3 /s). Daily flow analyses show high fluctuation during the warm season and very low flow during the cold season; the ten-year average analyses of daily flow at Pilot Station show a small increase in the peak and its timing shifted to a little earlier date. The annual flow, average of 227,900 ft 3 /s (6450 m 3 /s) with high interannual fluctuations, has increased by 18,200 ft 3 /s (or 8%; 520 m 3 /s) during 1977–2006. From 1977 to 2006, basin temperature in June has increased by 3.9 °F (2.2 °C) and decreased by 10.5 °F (5.8 °C) in January. A strong and positive correlation exists between air temperature in April and discharge in May; while a strong and negative correlation relates August temperature and September discharge. Negative trend during 1977–2006 is observed for precipitation in June (0.6 in; 15 mm) with a confidence over 93%. Precipitation in August and September has strong and positive correlations with discharge in September and October at basin outlet; the precipitation in other months has weak correlation with the discharge. The mean annual precipitation during 1977–2006 increased by 1.1 in (or 8%; 28 mm), which contributes to the annual flow increase during the study period. Copyright © 2012 John Wiley & Sons, Ltd.