499 research outputs found
Genetic Control of Immune Responsiveness: A Review of Its use as a Tool for Selection for Disease Resistance
Disease resistance and immune responsiveness have been traits generally ignored by animal breeders. Recent advances in immunology and molecular biology have opened new avenues towards our understanding of genetic control of these traits. The major histocompatibility gene complex (MHC) appears to play a central role in all immune functions and disease resistance. The need to understand the relationship between immune responsiveness, disease resistance and production traits is discussed in this review. Antagonistic relationships might prevent simultaneous improvement of all of these traits by conventional breeding methods. It is suggested that genetic engineering methods may allow the simultaneous improvement of disease resistance and production traits in domestic animals. Genes of the MHC will be especially good candidates for genetic engineering experiments to improve domestic species
Temporal Variations of Strength and Location of the South Atlantic Anomaly as Measured by RXTE
The evolution of the particle background at an altitude of ~540 km during the
time interval between 1996 and 2007 is studied using the particle monitor of
the High Energy X-ray Timing Experiment on board NASA's Rossi X-ray Timing
Explorer. A special emphasis of this study is the location and strength of the
South Atlantic Anomaly (SAA). The size and strength of the SAA are
anti-correlated with the the 10.7 cm radio flux of the Sun, which leads the SAA
strength by ~1 year reflecting variations in solar heating of the upper
atmosphere. The location of the SAA is also found to drift westwards with an
average drift rate of about 0.3 deg/yr following the drift of the geomagnetic
field configuration. Superimposed to this drift rate are irregularities, where
the SAA suddenly moves eastwards and where furthermore the speed of the drift
changes. The most prominent of these irregularities is found in the second
quarter of 2003 and another event took place in 1999. We suggest that these
events are previously unrecognized manifestations of the geomagnetic jerks of
the Earth's magnetic field.Comment: 21 pages, 11 figures, accepted for publication in Earth and Planetary
Science Letter
Genetic Control of Immune Response to Pseudorabies and Atrophic Rhinitis Vaccines: I. Heterosis, General Combining Ability and Relationship to Growth and Backfat
Data from 988 pigs from 119 litters farrowed in two seasons of a three-breed diallel crossbreeding experiment were analyzed to estimate general combining abilities of breeds and heterosis for humoral immune response to pseudorabies virus and atrophic rhinitis vaccines. Twenty purebred boars and 85 sows of the Duroc, Landrace and Yorkshire breeds were mated to provide the nine breed-of-sire and breed-of-dam combinations. Immune response was measured after vaccination. A modified-live pseudorabies virus (PR) vaccine was administered to piglets at 28 d of age and response measured as log2 serum neutralization titers at 56 d. An inactivated B. bronchiseptica bacterin was administered at 28, 42 and 112 d. Antibody levels were measured relative to positive and negative controls at 28, 56 and 119 d by using an enzyme-linked immunosorbent assay. The results of this study showed that ranking by breed of sire and breed of dam did not differ for general combining ability, and no evidence of significant heterosis for any immune responses was observed. Higher immune response at 56 d to B. bronchiseptica vaccine was associated with lower weaning weight (r = −.09, P\u3c.01). Correlations of days to 100 kg with 56-d and 119-d B. bronchiseptica antibody levels were .15 (P\u3c.01) and .12 (P\u3c.01). The relationship between humoral immune response to PR vaccine and growth traits was similar to that observed for B. bronchiseptica vaccine. Immune response to both antigens was not associated with backfat thickness. Further research using more specifically defined antigens and homogeneous populations of animals is needed to examine nonadditive gene action on the humoral immune response in swine
Genetic Control of Immune Response to Pseudorabies and Atrophic Rhinitis Vaccines: II: Comparison of Additive Direct and Maternal Genetic Effects
Data from 52 litters farrowed in two seasons of a cross-fostering experiment were analyzed to estimate variances and covariances for additive direct and maternal genetic effects on immune response to pseudorabies virus and B. bronchiseptica vaccine. Twenty purebred boars and 44 sows of the Duroc, Landrace and Yorkshire breeds were used. Immune response was measured after vaccine challenge. A modified-live pseudorabies (PR) vaccine was administered to piglets at 28 d of age; response was measured by log, serum neutralization titers at 56 d. An inactivated B. bronchiseptica bacterin was administered at 28, 42 and 112 d. Antibody levels were measured relative to positive and negative controls at 28, 56 and 119 d by using an enzyme-linked immunosorbent assay (ELISA). Results from this study for heritability were .18 ± .09 for PR titer and .15 ± .07 and .52 ± .15 for 56- and 119-d ELISA values, respectively. The variability due to nurse environment (maternal genetic variance and common environmental variance) as a percentage of phenotypic variance was 11.1% for PR titers and 29.6 and 8.8% for 56- and 119-d ELISA values, respectively. The heritabilities estimated in this study indicate that, if improved immune response to vaccines is desired, selection may be useful. However, the importance of maternal environment would make early selections less accurate than selections based on immune response measured later in life
Booster Main Engine Selection Criteria for the Liquid Fly-Back Booster
The Liquid Fly-Back Booster (LFBB) Program seeks to enhance the Space Shuttle system safety, performance and economy of operations through the use of an advanced, liquid propellant Booster Main Engine (BME). There are several viable BME candidates that could be suitable for this application. The objective of this study was to identify the key Criteria to be applied in selecting among these BME candidates. This study involved an assessment of influences on the overall LFBB utility due to variations in the candidate rocket-engines characteristics. This includes BME impacts on vehicle system weight, performance, design approaches, abort modes, margins of safety, engine-out operations, and maintenance and support concepts. Systems engineering analyses and trade studies were performed to identify the LFBB system level sensitivities to a wide variety of BME related parameters. This presentation summarizes these trade studies and the resulting findings of the LFBB design teams regarding the BME characteristics that most significantly affect the LFBB system. The resulting BME choice should offer the best combination of reliability, performance, reusability, robustness, cost, and risk for the LFBB program
The diminishing state of shared reality on US television news
The potential for a large, diverse population to coexist peacefully is
thought to depend on the existence of a ``shared reality:'' a public sphere in
which participants are exposed to similar facts about similar topics. A
generation ago, broadcast television news was widely considered to serve this
function; however, since the rise of cable news in the 1990s, critics and
scholars have worried that the corresponding fragmentation and segregation of
audiences along partisan lines has caused this shared reality to be lost. Here
we examine this concern using a unique combination of data sets tracking the
production (since 2012) and consumption (since 2016) of television news content
on the three largest cable and broadcast networks respectively. With regard to
production, we find strong evidence for the ``loss of shared reality
hypothesis:'' while broadcast continues to cover similar topics with similar
language, cable news networks have become increasingly distinct, both from
broadcast news and each other, diverging both in terms of content and language.
With regard to consumption, we find more mixed evidence: while broadcast news
has indeed declined in popularity, it remains the dominant source of news for
roughly 50\% more Americans than does cable; moreover, its decline, while
somewhat attributable to cable, appears driven more by a shift away from news
consumption altogether than a growth in cable consumption. We conclude that
shared reality on US television news is indeed diminishing, but is more robust
than previously thought and is declining for somewhat different reasons
Comparing Traditional and LLM-based Search for Consumer Choice: A Randomized Experiment
Recent advances in the development of large language models are rapidly
changing how online applications function. LLM-based search tools, for
instance, offer a natural language interface that can accommodate complex
queries and provide detailed, direct responses. At the same time, there have
been concerns about the veracity of the information provided by LLM-based tools
due to potential mistakes or fabrications that can arise in algorithmically
generated text. In a set of online experiments we investigate how LLM-based
search changes people's behavior relative to traditional search, and what can
be done to mitigate overreliance on LLM-based output. Participants in our
experiments were asked to solve a series of decision tasks that involved
researching and comparing different products, and were randomly assigned to do
so with either an LLM-based search tool or a traditional search engine. In our
first experiment, we find that participants using the LLM-based tool were able
to complete their tasks more quickly, using fewer but more complex queries than
those who used traditional search. Moreover, these participants reported a more
satisfying experience with the LLM-based search tool. When the information
presented by the LLM was reliable, participants using the tool made decisions
with a comparable level of accuracy to those using traditional search, however
we observed overreliance on incorrect information when the LLM erred. Our
second experiment further investigated this issue by randomly assigning some
users to see a simple color-coded highlighting scheme to alert them to
potentially incorrect or misleading information in the LLM responses. Overall
we find that this confidence-based highlighting substantially increases the
rate at which users spot incorrect information, improving the accuracy of their
overall decisions while leaving most other measures unaffected
Evaluating the scale, growth, and origins of right-wing echo chambers on YouTube
Although it is understudied relative to other social media platforms, YouTube
is arguably the largest and most engaging online media consumption platform in
the world. Recently, YouTube's outsize influence has sparked concerns that its
recommendation algorithm systematically directs users to radical right-wing
content. Here we investigate these concerns with large scale longitudinal data
of individuals' browsing behavior spanning January 2016 through December 2019.
Consistent with previous work, we find that political news content accounts for
a relatively small fraction (11%) of consumption on YouTube, and is dominated
by mainstream and largely centrist sources. However, we also find evidence for
a small but growing "echo chamber" of far-right content consumption. Users in
this community show higher engagement and greater "stickiness" than users who
consume any other category of content. Moreover, YouTube accounts for an
increasing fraction of these users' overall online news consumption. Finally,
while the size, intensity, and growth of this echo chamber present real
concerns, we find no evidence that they are caused by YouTube recommendations.
Rather, consumption of radical content on YouTube appears to reflect broader
patterns of news consumption across the web. Our results emphasize the
importance of measuring consumption directly rather than inferring it from
recommendations.Comment: 29 pages, 21 figures, 15 table
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