| 1. |
- Sha, Yongcui, et al.
(författare)
-
Diel vertical migration of copepods and its environmental drivers in subtropical Bahamian blue holes
- 2021
-
Ingår i: Aquatic Ecology. - : Springer. - 1386-2588 .- 1573-5125. ; 55:4, s. 1157-1169
-
Tidskriftsartikel (refereegranskat)abstract
- Diel vertical migration (DVM) is the most common behavioral phenomenon in zooplankton, and numerous studies have evaluated DVM under strong seasonality at higher latitudes. Yet, our understanding of the environmental drivers of DVM at low latitudes, where seasonal variation is less pronounced, remains limited. Therefore, we here examined patterns of vertical distribution in copepods in six subtropical Bahamian blue holes with different food web structure and tested the role of several key environmental variables potentially affecting this behavior. Day and night samplings showed that copepods generally performed DVM, characterized by downward migration to deeper depths during the day and upward migration to surface waters at night. Across all blue holes, the daytime vertical depth distribution of calanoid copepods correlated positively with both predation risk and depth of food resources (Chlorophyll a), but was less affected by ultraviolet radiation (UVR). A potential explanation is that since UVR is a continuous threat across seasons, zooplankton have established photoprotective pigmentation making them less vulnerable to this threat. The copepods also showed a size-structured depth segregation, where larger individuals were found at deeper depths during the day, which further strengthens the suggestion that predation is a major driver of DVM in these systems. Hence, in contrast to studies performed at higher latitudes, we show that despite the constant exposure to UVR, predator avoidance and food availability are the most pronounced drivers of copepod DVM at those low latitudes, suggesting that the main driver of DVM may vary among systems, but also systematically by latitude.
|
|
| 2. |
- Agui, A., et al.
(författare)
-
Direct observation of interface effects of thin AlAs(100) layers buried in GaAs
- 2000
-
Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 166:1-4, s. 309-312
-
Tidskriftsartikel (refereegranskat)abstract
- A study of the electronic structure of ultrathin AlAs layers buried in GaAs(100) and their interfaces is presented. Al L2,3 soft-X-ray-emission (SXE) spectra from the AlAs layers were measured. The spectra show distinct thickness-dependent features, which are reproduced using ab initio calculations.
|
|
| 3. |
- Chauhan, H. S., et al.
(författare)
-
Direct- and inverse-photoemission investigations of the electronic structure of Cd(0001)
- 1993
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 48:7, s. 4729-4734
-
Tidskriftsartikel (refereegranskat)abstract
- Photoemission and inverse angle-resolved photoemission spectra are presented for Cd(0001). The data are interpreted in terms of interband transitions, density-of-states effects, and excitations of surface states.
|
|
| 4. |
- Mankefors, S., et al.
(författare)
-
Ab initio calculations of soft-x-ray emission from Si(100) layers buried in GaAs
- 1998
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 58:16, s. 10551-10556
-
Tidskriftsartikel (refereegranskat)abstract
- Calculations of soft-x-ray emission spectra from Si(100) layers buried in GaAs are reported. The local densities of states for Si in As and Ga sites are found to be very different. By comparison with experimental data, this difference allows us to determine the relative amounts of Si in the two types of sites. In the case of a single Si layer we find that 63 (±5)% of the buried atoms are in Ga sites.
|
|
| 5. |
- Mankefors, S., et al.
(författare)
-
Theoretical investigation of soft x-ray emission from a Si(100) layer buried in GaAs
- 1998
-
Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 49:3, s. 181-184
-
Tidskriftsartikel (refereegranskat)abstract
- Calculations of the soft x-ray emission spectrum have been carried out on a buried Si(100) layer in GaAs and compared with experimental data. We find that Si occupies Ga- as well as As-sites and that the local density of states is different for these two cases.
|
|
| 6. |
- Mankefors, S., et al.
(författare)
-
Theoretical investigation of the thickness dependence of soft-x-ray emission from thin AlAs(100) layers buried in GaAs
- 2000
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 61:8, s. 5540-5545
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrathin AlAs(100) layers of 1-, 2-, and 5-ML thickness buried in GaAs are investigated by ab initio calculations. Unique experimental soft-x-ray emission spectra are explained in terms of interface effects and changes with layer thickness are found in the density of states. Only the central layer in the 5-ML geometry is bulklike. A valence-band offset of 0.53 eV is also found for this structure, while no offset exists in the 1- and 2-ML cases. Very good agreement is achieved between theory and experiment.
|
|
| 7. |
- Mankefors, S., et al.
(författare)
-
Theoretical investigations of As overlayers on InP(110) surfaces
- 1997
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 56:24, s. 15847-15852
-
Tidskriftsartikel (refereegranskat)abstract
- As adsorption and interaction with InP(110) is investigated by means of total-energy minimization calculations. We find that the As-P exchanged configuration has higher energy than the As/InP(110) epitaxially continued layer structure (ECLS), for all types of As reservoirs considered. In the presence of an additional As layer in ECLS (i.e., 1.5 ML adsorbed As), however, the exchanged configuration is only slightly higher in energy than the nonexchanged one. We conclude that the As-P exchange process is energetically unfavorable, and should in any case not be complete at room temperature, as suggested in a recent report. Our conclusion is supported by results of a photoemission study, including As adsorption, desorption, and redeposition, according to which the process is nonreversible.
|
|
| 8. |
- Nilsson, P. O., et al.
(författare)
-
Prediction of image-state excitation by secondary beams in inverse-photoemission spectroscopy
- 1993
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 47:19, s. 12968-12971
-
Tidskriftsartikel (refereegranskat)abstract
- Excitation of image states is predicted to occur frequently in inverse-photoemission spectroscopy due to diffracted electron beams traveling almost parallel to the surface. A simple kinematic model, as well as full calculations using inverse low-energy electron-diffraction theory, show the effect in the case of Cd(0001).
|
|
| 9. |
- Papadia, S., et al.
(författare)
-
Electronic structure of metallic superlattices : Mo/V
- 1992
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 45:4, s. 1857-1868
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure for a metallic superlattice system, Mo/V, has been calculated using the linear muffin-tin orbital method in the atomic-sphere approximation (ASA). Total energies have been calculated in the local-density approximation (LDA). Emphasis has been given to the electronic-density variation in these materials in order to understand hydrogen storage in metallic superlattices. It is found, within effective-medium theory, that the balance between charge transfer at the interfaces and volume changes of the constituents determines preferred hydrogen sites in Mo/V. Total-energy considerations favor a tetragonal distortion of the Mo/V superlattice over a cubic structure. Results for the LDA bands, charge transfer, and density of states are compared to other electronic-structure calculations of metallic superlattices, which gives rise to a consistent picture of electronic effects in these systems. The dependence of the results on the ASA is discussed. © 1992 The American Physical Society.
|
|
| 10. |
- Ritchie, A. J., et al.
(författare)
-
The Pseudomonas aeruginosa Quorum-Sensing Molecule N-3-(Oxododecanoyl)-L-Homoserine Lactone Inhibits T-Cell Differentiation and Cytokine Production by a Mechanism Involving an Early Step in T-Cell Activation
- 2005
-
Ingår i: Infection and Immunity. - : American Society for Microbiology. - 0019-9567 .- 1098-5522. ; 73:3, s. 1648-1655
-
Tidskriftsartikel (refereegranskat)abstract
- The Pseudomonas aeruginosa quorum-sensing molecule N-3-(oxododecanoyl)-L-homoserine lactone (OdDHL) has been reported to have immunomodulatory activity in several systems, although the mechanism of that activity remains to be fully characterized. We demonstrate here, using a defined in vitro model of antigen responses by T-cell receptor (TCR)-transgenic mouse splenic CD4 T cells, that the effect of OdDHL on activation and cytokine production is complete within 4 h of antigen or mitogen stimulation and does not depend on the insertion of OdDHL in the cell membrane, despite a previous report that immunosuppression by homoserine lactones required a minimum acyl chain length of 11 carbons (S. R. Chhabra, C. Harty, D. S. W. Hooi, M. Daykin, B. W. Bycroft, P. Williams, and D. Pritchard, J. Med. Chem. 46:97-104, 2003). We also demonstrate that while OdDHL can have toxic effects on nonlymphoid leukocytes, it does not induce significant cell death in T cells at the concentrations (≤10 µM) used in these experiments. In addition, we show that primary and secondary antigen-specific cytokine responses are equally susceptible to inhibition by OdDHL and that the compound inhibits the differentiation of both Th1 and Th2 cells. However, the precise balance of cytokine production by CD4 T cells stimulated in the presence of OdDHL varies with both the antigen concentration and its affinity for the transgenic TCR. Thus, conflicting reports of the nature of the immunosuppression by OdDHL may be due in part to the differences in antigen affinity and concentration in different models.
|
|
