Mechanical Properties Of Sediment Determine Burrowing Success And Influence Distribution Of Two Lugworm Species

We apply new perspectives on how organisms burrow by examining the association of in situ variation in sediment mechanical properties with burrowing ability and species distribution of two sympatric lugworms, Abarenicola pacifica and Abarenicola claparedi. We quantified the sediment\u27s resistance to penetration and its grain size distribution at sites inhabited by each species. Abarenicola pacifica individuals were found in significantly harder to penetrate, more heterogeneous sediments. We compared worm burrowing ability using reciprocal transplant experiments. Worms from firmer sediments, A. pacifica, were able to make successful steep burrows in sediments characteristic of either species. In contrast, A. claparedi individuals often failed to complete successful burrows in the firmer A. pacifica sediment. To examine how morphological differences could explain these patterns, we compared body wall musculature and measured how well individuals support their own bodies when draped over a cantilever. Lugworms from the firmer sediment had thicker body wall musculature and held their bodies more rigidly than did worms from softer sediments. Additionally, we observed subtle differences in the papillae on the proboscises\u27 surfaces, which could affect worm–sediment interactions, but we found no differences in the chaetae of the two species. Abarenicola claparedi produced more mucus, which could be important in shoring up burrow walls in their shifting, sandy habitat. This study presents the first example of using field-based experiments to determine how sediment mechanical properties and worm burrowing ability could act to determine organismal distribution. Our findings have broader ecological implications because of the role of lugworms as ecosystem engineers

Equivalence of Sobolev norms involving generalized Hardy operators

We consider the fractional Schr\"odinger operator with Hardy potential and critical or subcritical coupling constant. This operator generates a natural scale of homogeneous Sobolev spaces which we compare with the ordinary homogeneous Sobolev spaces. As a byproduct, we obtain generalized and reversed Hardy inequalities for this operator. Our results extend those obtained recently for ordinary (non-fractional) Schr\"odinger operators and have an important application in the treatment of large relativistic atoms.Comment: 16 pages; v2 contains improved results for positive coupling constant

Dialysis of Silicic Acid

This research was a quantative study of the polymerization of silicic acid molecules which occurred during the process of gel formation by the means of dialysis. The condensation of the silicic acid molecules, Si(OH)4, to form larger molecules of colloidal size, as suggested by the polysilicic acid fibriller theory, was investigated with membrances of known pore size at various stages of the reaction. Although filter and membrane action is only to a limited extent comparable with the action of a sieve, and is much more dependent on the absorption in the capillaries than the size of the pores, still a close connection between the concentration of membranes and the size of particles held back by them has been reported (1) and it was hoped that by this means the mechanism of the condensation of polysilicic acids could be studies to some extent

Evaluation of soft rubber goods

The performance of rubber goods suitable for use as O-rings, seals, gaskets, bladders and diaphragms under conditions simulating those of the space shuttle were studied. High reliability throughout the 100 flight missions planned for the space shuttle was considered of overriding importance. Accordingly, in addition to a rank ordering of the selected candidate materials based on prolonged fluid compatibility and sealability behavior, basic rheological parameters (such as cyclic hysteresis, stress relaxation, indicated modulus, etc.) were determined to develop methods capable of predicting the cumulative effect of these multiple reuse cycles

Intrinsic tethering activity of endosomal Rab proteins.

Rab small G proteins control membrane trafficking events required for many processes including secretion, lipid metabolism, antigen presentation and growth factor signaling. Rabs recruit effectors that mediate diverse functions including vesicle tethering and fusion. However, many mechanistic questions about Rab-regulated vesicle tethering are unresolved. Using chemically defined reaction systems, we discovered that Vps21, a Saccharomyces cerevisiae ortholog of mammalian endosomal Rab5, functions in trans with itself and with at least two other endosomal Rabs to directly mediate GTP-dependent tethering. Vps21-mediated tethering was stringently and reversibly regulated by an upstream activator, Vps9, and an inhibitor, Gyp1, which were sufficient to drive dynamic cycles of tethering and detethering. These experiments reveal a previously undescribed mode of tethering by endocytic Rabs. In our working model, the intrinsic tethering capacity Vps21 operates in concert with conventional effectors and SNAREs to drive efficient docking and fusion