Spatial-temporal Location Research Articles

Proximity-Based Security Techniques for Mobile Users in Wireless Networks

In this paper, we propose a privacy-preserving proximity-based security system for location-based services in wireless networks, without requiring any pre-shared secret, trusted authority, or public key infrastructure. In this system, the proximity-based authentication and session key establishment are implemented based on spatial temporal location tags. Incorporating the unique physical features of the signals sent from multiple ambient radio sources, the location tags cannot be easily forged by attackers. More specifically, each radio client builds a public location tag according to the received signal strength indicators, sequence numbers, and media access control (MAC) addresses of the ambient packets. Each client also keeps a secret location tag that consists of the packet arrival time information to generate the session keys. As clients never disclose their secret location tags, this system is robust against eavesdroppers and spoofers outside the proximity range. The system improves the authentication accuracy by introducing a nonparametric Bayesian method called infinite Gaussian mixture model in the proximity test and provides flexible proximity range control by taking into account multiple physical-layer features of various ambient radio sources. Moreover, the session key establishment strategy significantly increases the key generation rate by exploiting the packet arrival time of the ambient signals. The authentication accuracy and key generation rate are evaluated via experiments using laptops in typical indoor environments.

The Substance of Cinema

shapes directly onto filmstrips, paradigmatically is. Currie judges that purely abstract film stands in the same relation to cinema as setting afire a canvas prepared for painting stands to painting.5 Such pyro-painting might have some artistic merit but it is not painting per se. Likewise, nonpictorial movies created entirely by nonphotographic techniques are not so much movies as they are multifarious things you can do with the cinematic apparatus.6 Cinematic art, on Currie's thesis, diverges from painting in that it is necessarily imagistic and ontologically precludes genuine abstraction, construed along the lines of nondepiction combined with lack of reference. This seems more a metaphysical assumption than a description. His thesis also implies that depictive but nonphotographic animation techniques-from manually scratching pictures into the film's emulsion to digital animation-are uncinematic for all their pyrotechnics. I wonder if he has not expelled too much art from cinema, and cinema from art. I suspect, as does Carroll, that Cur i takes the etiology of one sort of movie as defi ing cinema in general. Thus he misses the ontologically primitive commonalities of superficially different artifacts. Or so I argue below. Carroll realizes that choice of definitive causal conditions might say more about normative presuppositions regarding the nature of cinema than about the nature of cinema itself. His solution to this problem is anti-essentialist, ingenious, and big hearted. But I doubt it is successful. Stated roughly, Carroll identifies as cinematic any two-dimensional presented in a detached display, generated by a template technology, and produced by cinematic means.7 He takes pains, though, to dissociate imagery from depiction. Indeed, he prefers moving image for its wider application to pictorial works (made photographically or otherwise) as well as purely abstract ones (including those made by such heteroclite methods as editing together strips of clear and opaque leader).8 Display detachment concerns the way cinematic and other images perforce involve spatial dislocation.9 Just by looking at a movie of it, I cannot orient my body in the Grand Canyon's direction. Unlike windows, mirrors, and magnifying lenses, photographically-produced movie pictures do not connect us spatially with their depicta. Say I am watching a movie at a spatialtemporal location Li. Following Carroll, when a display, D, at L1 is a photographically (or nonphotographically) generated picture of some extra-cinematic referent, S, D is detached from S's own space-time location L such that I cannot orient myself bodily and in time relative to S merely by looking D-wards at Li. But what if I were watching closed-circuit, live images of happenings in the room next door? As Carroll notes, background knowledge of the imagery's connection to that room, not visual experience of the image, allows one to orient one's self spatially-temporally to those happenings.o A template is a physical storage, recording, exhibition, or transmission format by means of which a cinematic work is disseminated. When I watch The Player (Robert Altman, 1992), I could be viewing imagery produced from a DVD, videocassette, broadcast television signal, or 35mm film print. None of these items is identical to the work, The Player, though. The work consists of story, characterization, irony, This content downloaded from 157.55.39.105 on Fri, 07 Oct 2016 04:28:50 UTC All use subject to http://about.jstor.org/terms Ponech The Substance of Cinema 189 actors' performances, directorial decisions, and so forth-properties and events no traces of which are found within the template's molecules and electrons. Similarly, were my copy of The Player destroyed or the TV signal degraded, the work itself would not thereby be destroyed-only one particular token of its template. Moreover, screening the show requires I view a mechanical performance executed from this template. At a stage play, visiting a movie set, or attending a hockey game, I watch people as they perform their artistic or professional actions right before my eyes. When I view a play, film, or game on television or in a movie theater my proximal perceptual object, the detached display, results from something a machine is arationally doing in front of me. This mechanical performance facilitates my access to peoples' artistic and sporting actions, but it is not itself an artistic or sporting perform-

Plasma blobs observed by ground‐based optical and radio techniques in the Brazilian tropical sector

Ground‐based optical and radio observations were carried out in the tropical region in Brazil, during the period from October 1998 to September 2000, and on several occasions we detected F‐region plasma blob (localized discrete plasma density enhancement) events. These are the first observations of blobs in the tropical F‐region using combined ground‐based optical and radio techniques. All‐sky images were used to map the spatial extension and temporal location of plasma blobs and ionosonde and photometer measurements were used to measure the plasma densities. Interesting cases of plasma blob events were observed on October 07, 1999 and March 04, 2000 over Cachoeira Paulista (22.7°S, 45.0°W; magnetic latitude 13.25°S, declination 20°W), showing discrete plasma density enhancements near regions of plasma density depletion structures in the OI 630.0 nm emission images. In these two cases, the electron densities were enhanced by a factor of, approximately, 2 above the background level. In this paper we report the first ground‐based observations of the plasma density enhancements, or blobs, and their association with equatorial spread‐F plasma depletions, and suggest a possible mechanism for their generation.

The Politics of Location: Where Am I Now?

In this article, through the use of several narrative devices, the author reflects on how the past remains in the present and shapes the future. Using the metaphor of locating oneself on a writing-map, she writes about fact and fiction, autobiography, and coauthor ship. The author finds that writing about one's spatial-temporal locations is a powerful tool for the relocation of the self—physically, symbolically, and emotionally.

Clonidine-induced antagonism of norepinephrine modulates the attentional processes involved in peak-interval timing.

Duke University The effects of the a2-agonist clonidine and the a2-antagonist idazoxan were studied with emphasis on the attentional mechanisms subserving interval-timing behavior. Administration of clonidine (0.015 mg/kg IP) to rats trained on a 20-s peak-interval (PI) timing procedure caused a rightward shift in peak functions, whereas idazoxan (0.15 mg/kg IP) caused a leftward shift. Rats were also trained on 10-s and 30-s baseline PI timing procedures in combination with the prior-entry and prior-entry reversal versions of this task that produced leftward shifts and rightward shifts relative to baseline training, respectively. Clonidine (0.025 mg/kg IP) produced a rightward shift in peak functions for all of these behavioral procedures. Taken together, these horizontal shifts in the peak functions indicate a decrease (leftward shift) or an increase (rightward shift) in the latency to start the internal clock that is influenced both by the attentional demands of the task and the effective level of brain norepinephrine. Cognitive accounts of information processing divide atten- tion into three major functions: orienting to sensory events, detecting signals for conscious processing, and maintaining an alert state (Posner & Petersen, 1990). The allocation of attention for the detection of signals for conscious processing may result in the subject attending to the expected spatial location, temporal location, or sensory modality of the signal. As a consequence, if the signal is either in an unexpected location or of an unexpected modality, it will not be processed as rapidly. In contrast, if attention is allocated to maintaining a general state of alertness or arousal, then any signal that is of sufficient intensity will engage conscious processing. An information-processing model of interval timing suggests Trevor B. Penney, Department of Psychology, Columbia University; Mark D. Holder, Department of Psychology, Memorial University of Newfoundland, St. John's, Newfoundland, Canada and Department of Psychology, Okanagan University College, Kelowna, British Columbia, Canada; Warren H. Meck, Department of Psychology: Experimental, Duke University. This research was supported in part by a grant from the Natural Sciences and Engineering Research Council of Canada (A1221). Preliminary reports based on this work were presented at the 64th Annual Meeting of the Eastern Psychological Association, Arlington, Virginia (Penney, Holder, M Meck, 1984). Data from human event-related potential (ERP) para- digms (e.g., Gratton et al., 1990) and animal timing tasks (Meck, 1984) suggest that warning signals serve to prime perceptual processing. Consequently, the use of warning signals can be used to influence a subject's expectation of thc stimulus properties (e.g., modality) of a forthcoming signal presentation. Central nervous system norepinephrine (NE) may accentu- ate activity of neurons that are transmitting the presence of significant stimuli and inhibit the activity of other neurons (Kety, 1970). This could be interpreted as an improvement in the signal-to-noise ratio or an enhancement of sclectivc attention. The selective attention hypothesis was initially based on the behavioral results of lesions to the dorsal noradrenergic bundle (DNAB; e.g., Mason, 1980; Robbins, Everitt, Cole, Archer, & Mohammed, 1985). This pathway originates in the pontine nucleus of the locus coeruleus (LC) and provides innervation to the spinal cord, cerebellum, and many forebrain areas including the caudate-putamen (Mason, 1980). The LC may act as an important gating mechanism for 82