8,715 research outputs found
Estimating commitment in a digital market place environment
The future generation of mobile communication shall be a convergence of mobile telephony and information systems which promises to change people's lives by enabling them to access information when, where and how they want. It presents opportunities to offer multimedia applications and services that meet end-toend service requirements. The Digital Marketplace framework will enable users to have separate contracts for different services on a per call basis. In order for such a framework to function appropriately, there has to be some means for the network operator to know in advance if its network will be able to support the user requirements. This paper discusses the methods by which the network operator will be able to determine if the system will be able to support another user of a certain service class and therefore negotiate parameters like commitment, QoS and the associated cost for providing the service, thus making the Digital Marketplace wor
Interactions involving D-branes
We investigate some aspects of the spectrum of D-branes and their
interactions with closed strings. As argued earlier, a collection of many
D-strings behaves, at large dilaton values, as a single multiply wound string.
We use this result and T-duality transformations to show that a similar
phenomenon occurs for effective strings produced by wrapping p-branes on a
small (p-1)-dimensional torus, for suitable coupling. To understand the decay
of an excited D-string at large dilaton values, we study the decay of an
elementary string at small dilaton values. A long string, multiply wound on a
circle, with a small excitation energy is found to predominantly decay into
another string with the same winding number and an unwound closed string
(rather than two wound strings). This decay amplitude agrees, under duality,
with the decay amplitude computed using the Born-Infeld action for the
D-string. We compute the absorption cross section for the D-brane model studied
by Callan and Maldacena. The absorption cross section for the dilaton equals
that for the scalars obtained by reduction of the graviton, and both agree with
the cross section expected from a classical hole with the same charges.Comment: harvmac, 23 pages; minor typos corrected and some clarifications
about the Born-Infeld action adde
Assessment and preliminary design of an energy buffer for regenerative braking in electric vehicles
Energy buffer systems, capable of storing the vehicle energy during braking and reusing this stored energy during acceleration, were examined. Some of these buffer systems when incorporated in an electric vehicle would result in an improvement in the performance and range under stop and go driving conditions. Buffer systems considered included flywheels, hydropneumatic, pneumatic, spring, and regenerative braking. Buffer ranking and rating criteria were established. Buffer systems were rated based on predicted range improvements, consumer acceptance, driveability, safety, reliability and durability, and initial and life cycle costs. A hydropneumatic buffer system was selected
The z=5.8 Quasar SDSSp J1044-0125: A Peek at Quasar Evolution?
The newly discovered z=5.8 quasar SDSSp J104433.04-012502.2 was recently
detected in X-rays and found to be extremely X-ray weak. Here we present the
hardness ratio analysis of the XMM-Newton observation. We consider various
models to explain the detection in the soft X-ray band and non-detection in the
hard band, together with its X-ray weakness. We show that the source may have a
steep power-law slope, with an absorber partially covering the continuum. This
may be X-ray evidence to support the argument of Mathur (2000) that narrow line
Seyfert 1 galaxies, which show steep power-law slopes, might be the low
redshift, low luminosity analogues of the high redshift quasars. Heavily
shrouded and steep X-ray spectrum quasars may indeed represent the early stages
of quasar evolution (Mathur 2000, Fabian 1999) and SDSSp J104433.04-012502.2 is
possibly giving us a first glimpse of the physical evolution of quasar
properties.Comment: To appear in A
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