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There are pressing reasons for developing a better understanding of net primary production (NPP) in the world's forests. These ecosystems play a large role in the world's carbon budget, and their dynamics, which are likely to be responding to global changes in climate and atmospheric composition, have major economic implications and impacts on global biodiversity. Although there is a long history of forest NPP studies in the ecological literature, current understanding of ecosystem-level production remains limited. Forest NPP cannot be directly measured; it must be approached by indirect methods. To date, field measurements have been largely restricted to a few aspects of NPP; methods are still lacking for field assessment of others, and past studies have involved confusion about the types of measurements needed. As a result, existing field-based estimates of forest NPP are likely to be significant underestimates.In this paper we provide a conceptual framework to guide efforts toward improved estimates of forest NPP. We define the quantity NPP* as the summed classes of organic material that should be measured or estimated in field studies for an estimate of total NPP. We discuss the above-and belowground components of NPP* and the available methods for measuring them in the field. We then assess the implications of the limitations of past studies for current understanding of NPP in forest ecosystems, discuss how field NPP* measurements can be used to complement tower-based studies of forest carbon flux, and recommend design criteria for future field studies of forest NPP.

The pivotal discovery that the death proteases caspase 8 (FLICE) and caspase 10 (Mch4/FLICE2) are recruited to the CD-95 and tumor necrosis factor receptor-1 signaling complexes suggested a mechanism used by these cytotoxic receptors to initiate apoptosis. In this report, we describe the cloning and characterization of I-FLICE, a novel inhibitor of tumor necrosis factor receptor-1-and CD-95-induced apoptosis. The overall architecture of I-FLICE is strikingly similar to that of FLICE and Mch4/FLICE2. However, I-FLICE lacks both a catalytic active site and residues that form the substrate binding pocket, in keeping with its dominant negative inhibitory function. I-FLICE is the first example of a catalytically inert caspase that can inhibit apoptosis.The cell death machinery is conserved throughout evolution and is composed of activators, inhibitors, and effectors (1). The effector arm of the cell death pathway is composed of a rapidly growing family of cysteine aspartate-specific proteases termed caspases (2). As implied by the name, these cysteine proteases cleave substrates following an aspartate residue (2, 3). Caspases are normally present as single polypeptide zymogens and contain an N-terminal prodomain and large and small catalytic subunits (4 -6). The two-chain active enzyme (composed of the large and small subunits) is obtained following proteolytic processing at internal Asp residues (4 -6). As such, caspases are capable of activating each other in a manner analogous to zymogen activation that is observed in the coagulation cascade (7). The identification of FLICE and Mch4/ FLICE2 as receptor-associated caspases suggested a surprisingly direct mechanism for activation of the death pathway by the cytotoxic receptors CD-95 and TNFR-1 1 (7-10). Upon activation, both receptors use their death domains to bind the corresponding domain in the adaptor molecule FADD (Fasassociated death domain protein) (8 -10). Dominant negative versions of FADD that lack the N-terminal segment but still retain the death domain potently inhibit both CD-95-and TNFR-1-induced apoptosis (11,12). Given the importance of the N-terminal segment in engaging the death pathway, it has been termed the death effector domain (DED) (11).Remarkably, the DED is present within the prodomain of FLICE and Mch4/FLICE2, and mutagenesis studies suggest that a homophilic interaction between the DED of FADD and the corresponding domain in FLICE or Mch4/FLICE2 is responsible for the recruitment of these proteases to the CD-95 and TNFR-1 signaling complexes (8 -11). Taken together, these data are consistent with FLICE and Mch4/FLICE2 being apical enzymes that initiate precipitous proteolytic processing of downstream caspases resulting in apoptosis (7,(13)(14)(15). A number of viral gene products antagonize CD-95-and TNFR-1-mediated killing as a means to persist in the infected host (16). The poxvirus-encoded serpin CrmA and baculovirus gene product p35 are direct caspase inhibitors (3). In contrast, the molluscum contagiosum virus protein MC159 and the e...

Abstract-Recently, it has been shown that CSMAtype random access algorithms can achieve the maximum possible throughput in wireless ad hoc networks. However, the delay performance of these algorithms can be quite bad. On the other hand, although some simple heuristics (such as distributed approximations of greedy maximal scheduling) can yield much better delay performance for a large set of arrival rates, they may only achieve a fraction of the capacity region in general. In this paper, we propose a discrete-time version of the CSMA-type random access algorithm that allows us to incorporate simple heuristics which lead to very good delay performance while retaining the throughput-optimality property. Central to our results is a discrete-time distributed randomized algorithm that generates data transmission schedules according to a product-form distribution, a counterpart of similar results obtained earlier for continuous-time models under the perfect CSMA assumption where collisions can never occur. An appealing feature of this algorithm is that it explicitly takes collisions into account during the exchange of control packets.