1,823 research outputs found
Use of high-intensity data to define large river management units: A case study on the lower Waikato River, New Zealand
The importance of environmental heterogeneity in lotic ecosystems is well recognised in river management, and continues to underpin studies of hierarchical patch dynamics, geomorphology and landscape ecology. We evaluated how physical characteristics and water chemistry measurements at high spatiotemporal resolution define channel units of potential ecological importance along 134 km of the lower Waikato River in North Island, New Zealand. We used multivariate hierarchical clustering to classify river reaches in an a priori unstructured manner based on (i) high-frequency, along-river water quality measurements collected in four seasons and (ii) river channel morphology data resolved from aerial photos for 1-km long reaches. Patterns of channel character were shaped by the depth and lateral complexity of constituent river reaches, while water quality patterns were represented by differences in clarity, chlorophyll fluorescence and specific conductance driven by tributary inflows in the mid-section of the river and tidal cycles in the lower section. Management units defined by physical characteristics or water quality did not necessarily align with boundaries typically reflecting clinal processes (e.g. tidal influence) or geomorphic, network or anthropogenic discontinuities. The results highlight the dynamic spatial and temporal properties of large rivers and the need to define clear objectives when deriving spatial units for management and research. Given that actions and targets for physical channel and water quality management may differ, the spatial extent identified for each of these does not necessarily need to directly coincide, although both should be considered in decision making and experimental design
X-ray Emission From Nearby M-dwarfs: the Super-saturation Phenomenon
A rotation rate and X-ray luminosity analysis is presented for rapidly
rotating single and binary M-dwarf systems. X-ray luminosities for the majority
of both single & binary M-dwarf systems with periods below days
(equatorial velocities, V 6 km~s) are consistent with the
current rotation-activity paradigm, and appear to saturate at about
of the stellar bolometric luminosity. The single M-dwarf data show tentative
evidence for the super-saturation phenomenon observed in some ultra-fast
rotating ( 100 km~s) G & K-dwarfs in the IC 2391, IC 2602 and Alpha
Persei clusters. The IC 2391 M star VXR60b is the least X-ray active and most
rapidly rotating of the short period (P 2 days) stars considered
herein, with a period of 0.212 days and an X-ray activity level about 1.5 sigma
below the mean X-ray emission level for most of the single M-dwarf sample. For
this star, and possibly one other, we cautiously believe that we have
identified the first evidence of super-saturation in M-dwarfs. If we are wrong,
we demonstrate that only M-dwarfs rotating close to their break up velocities
are likely to exhibit the super-saturation effect at X-ray wavelengths.Comment: 12 pages, 4 figures, accepted by MNRA
ISU Percussion Ensemble
Kemp Recital Hall Sunday Afternoon March 26, 1995 3:30p.m
Arterial Oxygen Saturation During Ascent to 5010 m: Heart Rate and AMS Scores
The hypothesis here is that tissues exposed to the hypoxia of altitude have increased blood flow so that the rate of arrival of oxygen is as rapid as normal. If the ascent is too rapid, the system starts to fail. The study involves an ascent to high altitude (5010 m) during which 59 subjects recorded their resting arterial oxygen saturation (SaO2), heart rate (HR) and Lake Louise acute mountain sickness (AMS) scores, twice daily. During the major ascent SaO2 fell progressively. In 42 subjects, HR increased in a highly significant, negative, relationship to SaO2. In 10 subjects heart rate (HR) remained unchanged. Three subjects showed extreme HR variability. Data were incomplete in four subjects. For nine of the subjects, showing the progressive HR versus SaO2 correlation during ascent, the sequence terminated with a lower HR than would be expected from the correlation so far. Individual AMS scores showed no correlation with SaO2 but averaged values from 19 of the subjects from each ‘one night’ stopover; showed a strong, negative, correlation. Average stopover HR values correlated negatively with the average SaO2 values. Cardiac output (CO) is likely to have increased during ascent as HR increased, since there is a progressive relationship between HR and cardiac output (CO). Hence, despite the progressive fall in SaO2, tissue oxygen delivery (DO2) would have remained close to normal in the 42 subjects who showed the significant HR: SaO2 relationship
A new upper limit on the reflected starlight from Tau Bootis b
Using improved doppler tomographic signal-analysis techniques we have carried
out a deep search for starlight reflected from the giant planet orbiting the
star Tau Bootis. We combined echelle spectra secured at the 4.2 m William
Herschel telescope in 1998 and 1999 (which yielded a tentative detection of a
reflected starlight component from the orbiting companion) with new data
obtained in 2000 (which failed to confirm the detection). The combined dataset
comprises 893 high resolution spectra with a total integration time of 75 hr 32
min spanning 17 nights. We establish an upper limit on the planet's geometric
albedo p<0.39 (at the 99.9 % significance level) at the most probable orbital
inclination i=36 degrees, assuming a grey albedo, a Venus-like phase function
and a planetary radius R_p=1.2 R_Jup. We are able to rule out some combinations
of the predicted planetary radius and atmospheric albedo models with high,
reflective cloud decks. Although a weak candidate signal appears near to the
most probable radial velocity amplitude, its statistical significance is
insufficient for us to claim a detection with any confidence.Comment: 13 pages, 18 figures, MNRAS accepted 12 June 200
Effects of traumatic brain injury on cognitive functioning and cerebral metabolites in HIV-infected individuals.
We explored the possible augmenting effect of traumatic brain injury (TBI) history on HIV (human immunodeficiency virus) associated neurocognitive complications. HIV-infected participants with self-reported history of definite TBI were compared to HIV patients without TBI history. Groups were equated for relevant demographic and HIV-associated characteristics. The TBI group evidenced significantly greater deficits in executive functioning and working memory. N-acetylaspartate, a putative marker of neuronal integrity, was significantly lower in the frontal gray matter and basal ganglia brain regions of the TBI group. Together, these results suggest an additional brain impact of TBI over that from HIV alone. One clinical implication is that HIV patients with TBI history may need to be monitored more closely for increased risk of HIV-associated neurocognitive disorder signs or symptoms
The On/Off Nature of Star-Planet Interactions
Evidence suggesting an observable magnetic interaction between a star and its
hot Jupiter appears as a cyclic variation of stellar activity synchronized to
the planet's orbit. In this study, we monitored the chromospheric activity of 7
stars with hot Jupiters using new high-resolution echelle spectra collected
with ESPaDOnS over a few nights in 2005 and 2006 from the CFHT. We searched for
variability in several stellar activity indicators (Ca II H, K, the Ca II
infrared triplet, Halpha, and He I). HD 179949 has been observed almost every
year since 2001. Synchronicity of the Ca II H & K emission with the orbit is
clearly seen in four out of six epochs, while rotational modulation with
P_rot=7 days is apparent in the other two seasons. We observe a similar
phenomenon on upsilon And, which displays rotational modulation (P_rot=12 days)
in September 2005, in 2002 and 2003 variations appear to correlate with the
planet's orbital period. This on/off nature of star-planet interaction (SPI) in
the two systems is likely a function of the changing stellar magnetic field
structure throughout its activity cycle. Variability in the transiting system
HD 189733 is likely associated with an active region rotating with the star,
however, the flaring in excess of the rotational modulation may be associated
with its hot Jupiter. As for HD 179949, the peak variability as measured by the
mean absolute deviation for both HD 189733 and tau Boo leads the sub-planetary
longitude by 70 degrees. The tentative correlation between this activity and
the ratio of Mpsini to the planet's rotation period, a quantity proportional to
the hot Jupiter's magnetic moment, first presented in Shkolnik et al. 2005
remains viable. This work furthers the characterization of SPI, improving its
potential as a probe of extrasolar planetary magnetic fields.Comment: Accepted for publication in the Astrophysical Journa
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