12,170 research outputs found
Exploring Deep Space: Learning Personalized Ranking in a Semantic Space
Recommender systems leverage both content and user interactions to generate
recommendations that fit users' preferences. The recent surge of interest in
deep learning presents new opportunities for exploiting these two sources of
information. To recommend items we propose to first learn a user-independent
high-dimensional semantic space in which items are positioned according to
their substitutability, and then learn a user-specific transformation function
to transform this space into a ranking according to the user's past
preferences. An advantage of the proposed architecture is that it can be used
to effectively recommend items using either content that describes the items or
user-item ratings. We show that this approach significantly outperforms
state-of-the-art recommender systems on the MovieLens 1M dataset.Comment: 6 pages, RecSys 2016 RSDL worksho
Re-identification of c. 15 700 cal yr BP tephra bed at Kaipo Bog, eastern North Island: implications for dispersal of Rotorua and Puketarata tephra beds.
A 10 mm thick, c. 15 700 calendar yr BP (c. 13 100 14C yr BP) rhyolitic tephra bed in the well-studied montane Kaipo Bog sequence of eastern North Island was previously correlated with Maroa-derived Puketarata Tephra. We revise this correlation to Okataina-derived Rotorua Tephra based on new compositional data from biotite phenocrysts and glass. The new correlation limits the known dispersal of Puketarata Tephra (sensu stricto, c. 16 800 cal yr BP) and eliminates requirements to either reassess its age or to invoke dual Puketarata eruptive events. Our data show that Rotorua Tephra comprises two glass-shard types: an early-erupted low-K2O type that was dispersed mostly to the northwest, and a high-K2O type dispersed mostly to the south and southeast, contemporary with late-stage lava extrusion. Late-stage Rotorua eruptives contain biotite that is enriched in FeO compared with biotite from Puketarata pyroclastics. The occurrence of Rotorua Tephra in Kaipo Bog (100 km from the source) substantially extends its known distribution to the southeast. Our analyses demonstrate that unrecognised syn-eruption compositional and dispersal changes can cause errors in fingerprinting tephra deposits. However, the compositional complexity, once recognised, provides additional fingerprinting criteria, and also documents magmatic and dispersal processes
Initial states and infrared physics in locally de Sitter spacetime
The long wavelength physics in a de Sitter region depends on the initial
quantum state. While such long wavelength physics is under control for massive
fields near the Hartle-Hawking vacuum state, such initial states make unnatural
assumptions about initial data outside the region of causal contact of a local
observer. We argue that a reasonable approximation to a maximum entropy state,
one that makes minimal assumptions outside an observer's horizon volume, is one
where a cutoff is placed on a surface bounded by timelike geodesics, just
outside the horizon. For sufficiently early times, such a cutoff induces
secular logarithmic divergences with the expansion of the region. For massive
fields, these effects sum to finite corrections at sufficiently late times. The
difference between the cutoff correlators and Hartle-Hawking correlators
provides a measure of the theoretical uncertainty due to lack of knowledge of
the initial state in causally disconnected regions. These differences are
negligible for primordial inflation, but can become significant during epochs
with very long-lived de Sitter regions, such as we may be entering now.Comment: 19 pages, 4 figures, references adde
Effects of cosmic rays on single event upsets
Assistance was provided to the Brookhaven Single Event Upset (SEU) Test Facility. Computer codes were developed for fragmentation and secondary radiation affecting Very Large Scale Integration (VLSI) in space. A computer controlled CV (HP4192) test was developed for Terman analysis. Also developed were high speed parametric tests which are independent of operator judgment and a charge pumping technique for measurement of D(sub it) (E). The X-ray secondary effects, and parametric degradation as a function of dose rate were simulated. The SPICE simulation of static RAMs with various resistor filters was tested
AdS/CFT and the Information Paradox
The information paradox in the quantum evolution of black holes is studied
within the framework of the AdS/CFT correspondence. The unitarity of the CFT
strongly suggests that all information about an initial state that forms a
black hole is returned in the Hawking radiation. The CFT dynamics implies an
information retention time of order the black hole lifetime. This fact
determines many qualitative properties of the non-local effects that must show
up in a semi-classical effective theory in the bulk. We argue that no
violations of causality are apparent to local observers, but the semi-classical
theory in the bulk duplicates degrees of freedom inside and outside the event
horizon. Non-local quantum effects are required to eliminate this redundancy.
This leads to a breakdown of the usual classical-quantum correspondence
principle in Lorentzian black hole spacetimes.Comment: 16 pages, harvmac, reference added, minor correction
Stratigraphy and chronology of a 15ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand.
We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) old at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 +/- 15 to 14 700 +/- 95 14C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferromagnesian silicate mineral assemblages, glass-shard major element composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (lateglacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene)
On Recognizing Transparent Objects in Domestic Environments Using Fusion of Multiple Sensor Modalities
Current object recognition methods fail on object sets that include both
diffuse, reflective and transparent materials, although they are very common in
domestic scenarios. We show that a combination of cues from multiple sensor
modalities, including specular reflectance and unavailable depth information,
allows us to capture a larger subset of household objects by extending a state
of the art object recognition method. This leads to a significant increase in
robustness of recognition over a larger set of commonly used objects.Comment: 12 page
Remote sensing in Michigan for land resource management
The utilization of NASA earth resource survey technology as an important aid in the solution of current problems in resource management and environmental protection in Michigan is discussed. Remote sensing techniques to aid Michigan government agencies were used to achieve the following results: (1) provide data on Great Lakes beach recession rates to establish shoreline zoning ordinances; (2) supply technical justification for public acquisition of land to establish the St. John's Marshland Recreation Area; (3) establish economical and effective methods for performing a statewide wetlands survey; (4) accomplish a variety of regional resource management actions in the Upper Peninsula; and (5) demonstrate improved soil survey methods. The project disseminated information on remote sensing technology and provided advice and assistance to a number of users in Michigan
Extracting Spooky-activation-at-a-distance from Considerations of Entanglement
Following an early claim by Nelson & McEvoy \cite{Nelson:McEvoy:2007}
suggesting that word associations can display `spooky action at a distance
behaviour', a serious investigation of the potentially quantum nature of such
associations is currently underway. This paper presents a simple quantum model
of a word association system. It is shown that a quantum model of word
entanglement can recover aspects of both the Spreading Activation equation and
the Spooky-activation-at-a-distance equation, both of which are used to model
the activation level of words in human memory.Comment: 13 pages, 2 figures; To appear in Proceedings of the Third Quantum
Interaction Symposium, Lecture Notes in Artificial Intelligence, vol 5494,
Springer, 200
Comments on the black hole information problem
String theory provides numerous examples of duality between gravitational
theories and unitary gauge theories. To resolve the black hole information
paradox in this setting, it is necessary to better understand how unitarity is
implemented on the gravity side. We argue that unitarity is restored by
nonlocal effects whose initial magnitude is suppressed by the exponential of
the Bekenstein-Hawking entropy. Time-slicings for which effective field theory
is valid are obtained by demanding the mutual back-reaction of quanta be small.
The resulting bounds imply that nonlocal effects do not lead to observable
violations of causality or conflict with the equivalence principle for
infalling observers, yet implement information retrieval for observers who stay
outside the black hole.Comment: 18 pages, 2 figures, revtex, v2 figure added and some improvements to
presentatio
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