104,826 research outputs found
Status Updates Over Unreliable Multiaccess Channels
Applications like environmental sensing, and health and activity sensing, are
supported by networks of devices (nodes) that send periodic packet
transmissions over the wireless channel to a sink node. We look at simple
abstractions that capture the following commonalities of such networks (a) the
nodes send periodically sensed information that is temporal and must be
delivered in a timely manner, (b) they share a multiple access channel and (c)
channels between the nodes and the sink are unreliable (packets may be received
in error) and differ in quality.
We consider scheduled access and slotted ALOHA-like random access. Under
scheduled access, nodes take turns and get feedback on whether a transmitted
packet was received successfully by the sink. During its turn, a node may
transmit more than once to counter channel uncertainty. For slotted ALOHA-like
access, each node attempts transmission in every slot with a certain
probability. For these access mechanisms we derive the age of information
(AoI), which is a timeliness metric, and arrive at conditions that optimize AoI
at the sink. We also analyze the case of symmetric updating, in which updates
from different nodes must have the same AoI. We show that ALOHA-like access,
while simple, leads to AoI that is worse by a factor of about 2e, in comparison
to scheduled access
Designing Primary Prevention for People Living with HIV
Today, there are new reasons for a sharper focus on prevention for people living with HIV. Growing numbers of people with the disease are living more healthy, sexual lives. Recent evidence suggests that risk taking among both HIV-positive and negative people is increasing. After nearly two decades of life in the shadow of AIDS, communities are growing weary of traditional prevention messages and many people are openly grappling with difficult questions of intimacy and sex. Increasingly, people living with HIV also face multiple complex economic and substance abuse challenges that complicate prevention efforts.There is an urgent need -- and sufficient expertise -- to move forward with prevention campaigns focused on helping people living with HIV and AIDS avoid passing their infection along to others. Numerous innovative interventions for people with HIV show promise, including:a social marketing campaign for gay men and a five-session group intervention for women living with HIV in Massachusetts,a chat line for positives and a group session program for Latinas/Latinos in Los Angeles,Internet chat room interventions in Atlanta,a group session for gay Asian American-Pacific Islander Americans living with HIV in San Francisco, andPrevention Case Management programs newly funded by the Centers for Disease Control
Buzz: Face-to-Face Contact and the Urban Economy
This paper argues that existing models of urban concentrations are incomplete unless grounded in the most fundamental aspect of proximity; face-to-face contact. Face-to-face contact has four main features; it is an efficient communication technology; it can help solve incentive problems; it can facilitate socialization and learning; and it provides psychological motivation. We discuss each of these features in turn, and develop formal economic models of two of them. Face-to-face is particularly important in environments where information is imperfect, rapidly changing, and not easily codified, key features of many creative activities.Agglomeration, clustering, urban economics, face-to-face
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