465 research outputs found
Geography Education Virtual Trunk
In order to access the Geography Education Virtual Trunk (GEVT), download the .zip file below. Make sure to extract all files to the same folder.
Open the file:
GEVT/index/indexd.htm
from the file manager or in a web browser program
The ecological distribution of monitor lizards (Reptilia, Varanidaej in Nigeria
The ecological distribulion of three varanid lizards (Varanus exanthematicus, K niloticus niloticus, and V. niloticus ornatusj in Nigeria is studied in the present paper, from both literature records and long-term field ecological research. V. exanthematicus is present only in central and northern Nigeria, where it seerns to be widespread and locally cornrnon in the Guinea savanna vegetation zone, but rnay be found in several spots in the Sudan savanna and even in the Sahel savanna. V. n. ornatus is confined to the extreme south of the country, ¡.e. in the coastal mangrove and deltaic swamp rainforest habita%, and also in the moist lowland rainforest. The distribution of V. n. niloticus remains controversial. It is widespread in the Sudan savanna and in the Guinea savanna, but appears only rarely in the derived savanna and rnoist lowland forest vegetation zones. Despite a few old literature records, it seerns to be absent frorn the rainforest blocks of southern Nigeria. Annual precipitation regimes seem to condition greatly the general distribution patterns of the Nigerian varanids, which are quite generalist in terms of habitat preferences within each rnajor climatic-vegetation zone.
Key words: Varanidae, Distribution, Ecology, Nigeria.The ecological distribulion of three varanid lizards (Varanus exanthematicus, K niloticus niloticus, and V. niloticus ornatusj in Nigeria is studied in the present paper, from both literature records and long-term field ecological research. V. exanthematicus is present only in central and northern Nigeria, where it seerns to be widespread and locally cornrnon in the Guinea savanna vegetation zone, but rnay be found in several spots in the Sudan savanna and even in the Sahel savanna. V. n. ornatus is confined to the extreme south of the country, ¡.e. in the coastal mangrove and deltaic swamp rainforest habita%, and also in the moist lowland rainforest. The distribution of V. n. niloticus remains controversial. It is widespread in the Sudan savanna and in the Guinea savanna, but appears only rarely in the derived savanna and rnoist lowland forest vegetation zones. Despite a few old literature records, it seerns to be absent frorn the rainforest blocks of southern Nigeria. Annual precipitation regimes seem to condition greatly the general distribution patterns of the Nigerian varanids, which are quite generalist in terms of habitat preferences within each rnajor climatic-vegetation zone.
Key words: Varanidae, Distribution, Ecology, Nigeria.The ecological distribulion of three varanid lizards (Varanus exanthematicus, K niloticus niloticus, and V. niloticus ornatusj in Nigeria is studied in the present paper, from both literature records and long-term field ecological research. V. exanthematicus is present only in central and northern Nigeria, where it seerns to be widespread and locally cornrnon in the Guinea savanna vegetation zone, but rnay be found in several spots in the Sudan savanna and even in the Sahel savanna. V. n. ornatus is confined to the extreme south of the country, ¡.e. in the coastal mangrove and deltaic swamp rainforest habita%, and also in the moist lowland rainforest. The distribution of V. n. niloticus remains controversial. It is widespread in the Sudan savanna and in the Guinea savanna, but appears only rarely in the derived savanna and rnoist lowland forest vegetation zones. Despite a few old literature records, it seerns to be absent frorn the rainforest blocks of southern Nigeria. Annual precipitation regimes seem to condition greatly the general distribution patterns of the Nigerian varanids, which are quite generalist in terms of habitat preferences within each rnajor climatic-vegetation zone.
Key words: Varanidae, Distribution, Ecology, Nigeria
2MASS J05162881+2607387: A New Low-Mass Double-Lined Eclipsing Binary
We show that the star known as 2MASS J05162881+2607387 (hereafter J0516) is a
double-lined eclipsing binary with nearly identical low-mass components. The
spectroscopic elements derived from 18 spectra obtained with the High
Resolution Spectrograph on the Hobby-Eberly Telescope during the Fall of 2005
are K_1=88.45 +/- 0.48 km/s and K_2=90.43 +/- 0.60 km/s, resulting in a mass
ratio of$q=K_1/K_2 = 0.978 +/- 0.018 and minimum masses of M_1 sin^{3}i=0.775
+/- 0.016 solar masses and M_2 sin^{3}i=0.759 +/- 0.012 solar masses,
respectively. We have extensive differential photometry of J0516 obtained over
several nights between 2004 January-March (epoch 1) and 2004 October-2005
January plus 2006 January (epoch 2) using the 1m telescope at the Mount Laguna
Observatory. The source was roughly 0.1 mag brighter in all three bandpasses
during epoch 1 when compared to epoch 2. Also, phased light curves from epoch 1
show considerable out-of-eclipse variability, presumably due to bright spots on
one or both stars. In contrast, the phased light curves from epoch 2 show
little out-of-eclipse variability. The light curves from epoch 2 and the radial
velocity curves were analyzed using our ELC code with updated model atmospheres
for low-mass stars. We find the following: M_1=0.787 +/- 0.012 solar masses,
R_1=0.788 +/- 0.015 solar radii, M_2=0.770 +/- 0.009 solar masses, and
R_2=0.817 +/- 0.010 solar radii. The stars in J0516 have radii that are
significantly larger than model predictions for their masses, similar to what
is seen in a handful of other well-studied low-mass double-lined eclipsing
binaries. We compiled all recent mass and radius determinations from low-mass
binaries and determine an empirical mass-radius relation of the form R = 0.0324
+ 0.9343M + 0.0374M^2, where the quantities are in solar units.Comment: 16 pages, 10 figures (Figure 1 has degraded quality), to appear in
Ap
Coregulation of vascular tube stabilization by endothelial cell TIMP-2 and pericyte TIMP-3
The endothelial cell (EC)–derived tissue inhibitor of metalloproteinase-2 (TIMP-2) and pericyte-derived TIMP-3 are shown to coregulate human capillary tube stabilization following EC–pericyte interactions through a combined ability to block EC tube morphogenesis and regression in three-dimensional collagen matrices. EC–pericyte interactions strongly induce TIMP-3 expression by pericytes, whereas ECs produce TIMP-2 in EC–pericyte cocultures. Using small interfering RNA technology, the suppression of EC TIMP-2 and pericyte TIMP-3 expression leads to capillary tube regression in these cocultures in a matrix metalloproteinase-1 (MMP-1)–, MMP-10–, and ADAM-15 (a disintegrin and metalloproteinase-15)–dependent manner. Furthermore, we show that EC tube morphogenesis (lumen formation and invasion) is primarily controlled by the TIMP-2 and -3 target membrane type (MT) 1 MMP. Additional targets of these inhibitors include MT2-MMP and ADAM-15, which also regulate EC invasion. Mutagenesis experiments reveal that TIMP-3 requires its proteinase inhibitory function to induce tube stabilization. Overall, these data reveal a novel role for both TIMP-2 and -3 in the pericyte-induced stabilization of newly formed vascular networks that are predisposed to undergo regression and reveal specific molecular targets of the inhibitors regulating these events
- …