Ages of 24 widespread tephras erupted since 30,000 years ago in New Zealand, with re-evaluation of the timing and palaeoclimatic implications of the Lateglacial cool episode recorded at Kaipo bog

Tephras are important for the NZ-INTIMATE project because they link all three records comprising the composite inter-regional stratotype developed for the New Zealand climate event stratigraphy (NZ-CES). Here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30,000 calendar (cal.) years ago in New Zealand to help facilitate their use as chronostratigraphic dating tools for the NZ-CES and for other palaeoenvironmental and geological applications. The selected tephras comprise 12 rhyolitic tephras from Taupo, nine rhyolitic tephras from Okataina, one peralkaline rhyolitic tephra from Tuhua, and one andesitic tephra each from Tongariro and Egmont/Taranaki volcanic centres. Age models for the tephras were obtained using three methods: (i) 14C-based wiggle-match dating of wood from trees killed by volcanic eruptions (these dates published previously); (ii) flexible depositional modelling of a high-resolution 14C-dated age-depth sequence at Kaipo bog using two Bayesian-based modelling programs, Bacon and OxCal's P_Sequence function, and the IntCal09 data set (with SH offset correction -44 ± 17 yr); and (iii) calibration of 14C ages using OxCal's Tau_Boundary function and the SHCal04 and IntCal09 data sets. Our preferred dates or calibrated ages for the 24 tephras are as follows (youngest to oldest, all mid-point or mean ages of 95% probability ranges): Kaharoa AD 1314 ± 12; Taupo (Unit Y) AD 232 ± 10; Mapara (Unit X) 2059 ± 118 cal. yr BP; Whakaipo (Unit V) 2800 ± 60 cal. yr BP; Waimihia (Unit S) 3401 ± 108 cal. yr BP; Stent (Unit Q) 4322 ± 112 cal. yr BP; Unit K 5111 ± 210 cal. yr BP; Whakatane 5526 ± 145 cal. yr BP; Tuhua 6577 ± 547 cal. yr BP; Mamaku 7940 ± 257 cal. yr BP; Rotoma 9423 ± 120 cal. yr BP; Opepe (Unit E) 9991 ± 160 cal. yr BP; Poronui (Unit C) 11,170 ± 115 cal. yr BP; Karapiti (Unit B) 11,460 ± 172 cal. yr BP; Okupata 11,767 ± 192 cal. yr BP; Konini (bed b) 11,880 ± 183 cal. yr BP; Waiohau 14,009 ± 155 cal. yr BP; Rotorua 15,635 ± 412 cal. yr BP; Rerewhakaaitu 17,496 ± 462 cal. yr BP; Okareka 21,858 ± 290 cal. yr BP; Te Rere 25,171 ± 964 cal. yr BP; Kawakawa/Oruanui 25,358 ± 162 cal. yr BP; Poihipi 28,446 ± 670 cal. yr BP; and Okaia 28,621 ± 1428 cal. yr BP. Secondly, we have re-dated the start and end of the Lateglacial cool episode (climate event NZce-3 in the NZ-CES), previously referred to as the Lateglacial climate reversal, as defined at Kaipo bog in eastern North Island, New Zealand, using both Bacon and OxCal P_Sequence modelling with the IntCal09 data set. The ca 1200-yr-long cool episode, indicated by a lithostratigraphic change in the Kaipo peat sequence to grey mud with lowered carbon content, and a high-resolution pollen-derived cooling signal, began 13,739 ± 125 cal. yr BP and ended 12,550 ± 140 cal. yr BP (mid-point ages of the 95% highest posterior density regions, Bacon modelling). The OxCal modelling, generating almost identical ages, confirmed these ages. The Lateglacial cool episode (ca 13.8-12.6 cal. ka BP) thus overlaps a large part of the entire Antarctic Cold Reversal chronozone (ca 14.1-12.4 cal. ka BP or ca 14.6-12.8 cal. ka BP), and an early part of the Greenland Stadial-1 (Younger Dryas) chronozone (ca 12.9-11.7 cal. ka BP). The timing of the Lateglacial cool episode at Kaipo is broadly consistent with the latitudinal patterns in the Antarctic Cold Reversal signal suggested for the New Zealand archipelago from marine and terrestrial records, and with records from southern South America

High‐efficiency photovoltaic modules on a chip for millimeter‐scale energy harvesting

Photovoltaic modules at the millimeter scale are demonstrated in this work to power wirelessly interconnected millimeter‐scale sensor systems operating under low‐flux conditions, enabling applications in the Internet of things and biological sensors. Module efficiency is found to be limited by perimeter recombination for individual cells and shunt leakage for the series‐connected module configuration. We utilize GaAs and AlGaAs junction barrier isolation between interconnected cells to dramatically reduce shunt leakage current. A photovoltaic module with eight series‐connected cells and total area of 1.27 mm2 demonstrates a power conversion efficiency of greater than 26% under low‐flux near‐infrared illumination (850 nm at 1 μW/mm2). The output voltage of the module is greater than 5 V, providing a voltage up‐conversion efficiency of more than 90%. We demonstrate direct photovoltaic charging of a 16‐μAh pair of thin‐film lithium‐ion batteries under dim light conditions, enabling the perpetual operation of practical millimeter‐scale wirelessly interconnected systems.We demonstrate monolithic GaAs photovoltaic modules at the millimeter scale to efficiently power wirelessly interconnected millimeter‐scale sensor systems operating under low‐flux conditions. Eight series‐connected cells are used to provide an operating voltage of 5 V for direct battery charging. Module power conversion efficiency greater than 26% is achieved under weak 850‐nm near‐infrared illumination and 90% voltage up‐conversion efficiency utilizing AIGaAs junction barrier isolation as a critical technique in reducing shunt leakage current.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149283/1/pip3132_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149283/2/pip3132.pd

Direct Imaging and Spectroscopy of a Planetary Mass Candidate Companion to a Young Solar Analog

We present Gemini near-infrared adaptive optics imaging and spectroscopy of a planetary mass candidate companion to 1RXS J160929.1-210524, a roughly solar-mass member of the 5 Myr-old Upper Scorpius association. The object, separated by 2.22" or 330 AU at ~150 pc, has infrared colors and spectra suggesting a temperature of 1800(-100/+200) K, and spectral type of L4(-2/+1). The H- and K-band spectra provide clear evidence of low surface gravity, and thus youth. Based on the widely used DUSTY models, we infer a mass of 8(-2/+4)Mjupiter. If gravitationally bound, this would be the lowest mass companion imaged around a normal star thus far, and its existence at such a large separation would pose a serious challenge to theories of star and planet formation.Comment: Revised accepted version, ApJL, in pres

Analysis and mitigation of variability in subthreshold design

Subthreshold circuit design is a compelling method for ultra-low power applications. However, subthreshold designs show dramati-cally increased sensitivity to process variations due to the exponen-tial relationship of subthreshold drive current with Vth variation. In this paper, we present an analysis of subthreshold energy efficiency considering process variation, and propose methods to mitigate its impact. We show that, unlike superthreshold circuits, random dopant fluctuation is the dominant component of variation in subthreshold operation. We investigate how this variability can be ameliorated with proper circuit sizing and choice of circuit logic depth. We then present a statistical analysis of the energy efficiency of subthreshold circuits considering process variations. We show that the energy optimal supply voltage increases due to process variations and study its dependence on circuit parameters. We verify our analytical mod-els against Monte Carlo SPICE simulations and show that they accu-rately predict the minimum energy and energy optimal supply voltage. Finally, we use the developed statistical energy model to determine the optimal pipelining depth in subthreshold designs

Hi-Rise: A high-radix switch for 3D integration with single-cycle arbitration

Abstract-This paper proposes a novel 3D switch, called 'HiRise', that employs high-radix switches to efficiently route data across multiple stacked layers of dies. The proposed interconnect is hierarchical and composed of two switches per silicon layer and a set of dedicated layer to layer channels. However, a hierarchical 3D switch can lead to unfair arbitration across different layers. To address this, the paper proposes a unique class-based arbitration scheme that is fully integrated into the switching fabric, and is easy to implement. It makes the 3D hierarchical switch's fairness comparable to that of a flat 2D switch with least recently granted arbitration. The 3D switch is evaluated for different radices, number of stacked layers, and different 3D integration technologies. A 64-radix, 128-bit width, 4-layer Hi-Rise evaluated in a 32nm technology has a throughput of 10.65 Tbps for uniform random traffic. Compared to a 2D design this corresponds to a 15% improvement in throughput, a 33% area reduction, a 20% latency reduction, and a 38% energy per transaction reduction