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Open Access Publications from the University of California

Volume 13 Issue 1 2009

Issue cover


Implantable Devices

In science fiction, humans have conjured up numerous possibilities of semi-robotic, semi-humanoid beings: cyborgs, which are fictional beings that are part human, part robot; androids, or robots that look like and behave like human beings; automatons, which are humans who behave like machines; and bionic beings, or humans with organs or functions replaced or enhanced by electronically powered parts.


Evaluating The Effect Of Climate In A Sierran Mixed Conifer Forest

Forest growth and yield models such as CACTOS and PROGNOSIS have typically modeled future growth dynamics using unchanging climatic data. These models, applied to a future where the climate is changing, can lead to important discrepancies between actual and predicted growth rates. Yeh and Wensel (2000) first examined these discrepancies in CACTOS performance. They identified summer temperature and winter precipitation as key climatic variables influencing tree growth and developed indices to adjust growth based on the climate. However, the relationships established by Yeh and Wensel were formulated using the CACTOS growth simulator, an input-intensive growth and yield model. No independent validation of the climate-growth indices was conducted. This study examines the reliability of Yeh and Wensel’s climate adjustments to the growth model for forest management applications. Biological growth signals were removed from long-term annual growth records. These empirical records were derived from tree ring analyses. A smoothing spline was used to quantify the biological growth signal (i.e., low-frequency variation in increment). A climate signal (i.e. the residual) was derived by subtracting this spline from the long-term record. The resulting residuals were correlated against the predicted climate growth signal as given by Yeh and Wensel’s model. The correlation of climatic influence on growth for different species and crown classes was also considered. The results of this study indicate that Yeh and Wensel’s model provides growth estimates that reliably inform management decisions. However, the relationship between climate and growth is stronger in dominant tree classes, indicating that climate more predictably affects more dominant trees. For sub-dominant trees, climatic variables had little correlation. It does not appear that competition between dominant and sub-dominant trees is confounding the correlation between sub-dominant tree growth and climate. Suppressed or understory tree growth may be more dependent on edaphic and/or microclimate gradients.

The Impact Of Habitat Fragmentation On Bird Community Composition In Monteverde, Costa Rica

Habitat fragmentation is currently the greatest threat to the avifauna of Costa Rica. To study its effects on bird species composition in the Monteverde region, I surveyed three sites of varying degrees of fragmentation. I did not detect a significant difference in the species richness and heterogeneity among the three sites. My study showed, however, that the species composition changed drastically among sites. Furthermore, the predominant feeding guilds of the species unique to each site changed between sites, suggesting that food availability is an important determinant of where a bird lives. The proportion of insectivores was inversely related to fragmentation, and omnivores are perhaps less affected by fragmentation than other feeding guilds because they are able to use a higher variety of food resources. Certain species were only found at the more continuous sites, including the Black-breasted Wood-quail (Odontophorus leucolaemus), which implies they may be more sensitive to habitat fragmentation.

Ectoparasite Presence, Density, And Unit Load In Relation To Tent-roosting Behavior Of Neotropical Bats

Behavioral defenses have evolved in response to the negative effects caused by ectoparasitism. Within neotropical bats, roosting behaviors have been studied as a possible reaction to the presence of parasitic bat flies and mites. Tent-making, the process of actively constructing protective roosts in foliage, was studied in order to assess its specific impact on ectoparasitism. Bats that exclusively utilized tents were predicted to suffer a lower level of ectoparasitism as their roosting behavior can disrupt ectoparasite lifecycles. I captured different bat species, categorized as either tent-roosting or non-tent-roosting, at several sites in Costa Rica, including Monteverde, San Luis and Peñas Blancas. All ectoparasites were collected with forceps and ultimately used to calculate presence, density, and unit load. After analysis, the bat species grouped as tent-makers, Artibeus toltecus and Platyrrhinus helleri, contained significantly lower levels of ectoparasite presence, density, and load in comparison with the species of bats that do not exclusively use tent roosts. These results, though suggestive, are derived from a relatively small sample of tent-making bats and can be strengthened by further replication on a larger scale.

Evaluating Economizer Use In Data Centers

An emerging technology to alleviate rising energy demands for data centers are economizers, which turn off the power consuming chillers and bring in outside air for cooling. However, contaminants in outdoor air can lower the reliability of the electronics through corrosion, which can negate any energy savings. This experiment seeks to determine if the indoor air quality of economizer systems is suitable for data center use. The mass concentrations of the particulate matter were measured both inside and outside of the data center, using aerosol instruments. Particles were captured using collection filters, to identify their chemical properties. It is shown that indoor particle concentrations rise when the economizer is operating, due to bringing in outside air. However, the concentrations are well below the ASHRAE standard, which confirms that economizer use does not pose a risk for the servers in a data center.

Synaptic Plasticity: Spatio-Temporal Analysis Of Actin Dynamics

Glutamatergic synapses are highly modifiable, making them key targets in processes such as learning and memory. In crayfish glutamatergic neuromuscular junctions, hyperpolarization and cyclic nucleotide-activated (HCN) channels and actin cytoskeleton dynamics are critical intermediate factors in hormonal modulation of glutamatergic synapses which lead to cAMP (3’-5’-cyclic adenosine monophosphate)-dependent enhancement of synaptic transmission. Although models have been proposed, there has been a lack of experimental evidence on the relationship between HCN channels and the integrity of the actin cytoskeleton during cAMP-dependent enhancement. The specific goal of this study is to test the sequence of activation of the aforementioned mediators in synaptic enhancement via precisely controlled pharmacological experiments. At glutamatergic neuromuscular junctions of crayfish limb muscles, HCN channel activator, lamotrigine (50 μM), enhanced synaptic transmission about 20%. This enhancement was completely blocked with actin depolymerizer, latrunculin B (3 μM). These results support previous models of the temporal arrangement of events leading to synaptic enhancement, specifically that changes in actin cytoskeleton follow HCN channel activation. Concurrently, we are also using a spatio-temporal marker called phalloidin, a toxin which binds actin filaments, to further test the hypothesis that activation of HCNCs precedes actin cytoskeleton polymerization. This allows for manipulation of HCN channels and visualization of actin that could propose the associated molecular mechanisms. Preliminary evidence suggests actin reorganization.

The Effects Of Sleep On Implicit And Explicit Motor Skill Sequence Learning And Task Integration: A Literature Review And Pilot Study

Various studies have been conducted on implicit (unconscious) and explicit (conscious) motor skill sequence learning by means of serial reaction time tasks in order to understand the two learning systems in the human brain (Schimidtke & Heuer, 1996; Stickgold, 2003; Ivry, 2003). Although the effects of implicit learning, bimodal integration of tasks (task integration) and sleep on implicit motor skill learning have been explored in various combination, all three have yet to be studied in one research design. We conducted a pilot study in an attempt to investigate how these three mechanisms contribute to the implicit learning phenomenon. Results revealed that explicit sequence learners have overall quicker reaction times and more accurate responses. We also found a lower percentage of implicit learning during the less complex sequence tasks. Subsequent tests found that sleep had a significant effect on explicit sequence learning, but no significant effect on implicit sequence learning.