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| 2. |
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| 3. |
- Simancas, J.F., et al.
(author)
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The seismic crustal structure of the Ossa-Morena Zone and its geological interpretation
- 2004
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In: Journal of Iberian Geology. - 1698-6180 .- 1886-7995. ; 30, s. 133-142
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Journal article (peer-reviewed)abstract
- The IBERSEIS deep reflection seismic experiment has provided a crustal image of the Variscan orogen of southwest Iberia. A brief presentation of the entire seismic profile is given, and then the Ossa-Morena Zone (OMZ) and its boundaries are considered. The crust of the OMZ is shown to be divided into an upper crust, characterized by dominantly NE-dipping reflectivity, and a poorly reflective lower crust. The reflectivity of the upper crust has good correlation with the geological cross-section constructed from surface mapping. In the seismic image, the upper crustal geological structures are seen to merge in the middle crust. Nevertheless, the OMZ middle crust is not a mere detachment level, as it shows very unusual features: it appears as a band of strong reflectivity and irregular thickness (the Iberian Reflective Body, IRB) that we interpret as a great sill-like intrusion of basic rocks. The boundaries of the OMZ are considered sutures of the orogen, and their geometrical features, as deduced from geological mapping and the seismic image, are in accordance with the transpressional character of the Variscan collision recorded in SW Iberia. The present Moho is flat, obliterating the root of the orogen.
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| 6. |
- Sanchez, D., Garcia-Hernandez, M., Martinez, J.L., Alonso, J.A. Martinez-Lope, M.J., Casais, M.T., Mellergard, A.
(author)
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The effect of substitutional mis-site disorder on the structural, magnetic and electronic transport properties of Sr2FeMoO6 double perovskites
- 2002
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In: J. Magn. Magn. Mater.. ; 242, s. 729-731
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Journal article (peer-reviewed)
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| 7. |
- Bergmann, U. C., et al.
(author)
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On the beta-decay of C-9
- 2001
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In: Nuclear Physics A. - 0375-9474. ; 692:3-4, s. 427-450
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Journal article (peer-reviewed)abstract
- In beta -decay experiments on C-9 at CERN/ISOLDE the beta -strength was determined to the ground state, the 12.2 MeV excited state and the Isobaric Analog State (IAS) at 14.655 MeV in B-9. A large beta -strength asymmetry is deduced for the mirror transitions of C-9 and Li-9 to states around 12 MeV excitation energy. A satisfactory description of the three-body decay from a narrow energy region around the 12.2 MeV resonance is obtained within a sequential model involving the ground and first-excited states of Li-5 and Be-8. From the study of angular correlations the spin of the 12.2 MeV state is determined as 5/2(-). For the first time the population of the IAS is observed in beta -decay and new information on the decay of this state is obtained. The advantages of a closely packed. highly segmented detector setup are demonstrated. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 8. |
- Castellote, M, et al.
(author)
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In situ accelerated leaching of cement paste by application of electrical fields monitored by synchrotron X-ray diffraction
- 2004
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In: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630. ; 79:3, s. 661-669
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Journal article (peer-reviewed)abstract
- An external dc voltage was applied to a cured cement paste to simulate its natural degradation as a function of time. The electrical treatment was monitored in situ by simultaneous acquisition of diffraction patterns every 10 min. The analysis of the diffraction patterns has confirmed that the microstructure of the whole paste changes during the treatment, with precipitation and dissolution of several phases. This work contributes to the understanding of the fundamentals of the microstructure alterations that take place upon application of an electrical field, allowing the establishment of a first approach to the understanding of the mechanism of these changes.
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| 9. |
- Dickson, C. T., et al.
(author)
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Properties and role of I-h in the pacing of subthreshold oscillations in entorhinal cortex layer II neurons
- 2000
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In: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:5, s. 2562-2579
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Research review (peer-reviewed)abstract
- Various subsets of brain neurons express a hyperpolarization-activated inward current (I-h) that has been shown to be instrumental in pacing oscillatory activity at both a single-cell and a network level. A characteristic feature of the stellate cells (SCs) of entorhinal cortex (EC) layer II, those neurons giving rise to the main component of the perforant path input to the hippocampal formation, is their ability to generate persistent, Na+-dependent rhythmic subthreshold membrane potential oscillations, which are thought to be instrumental in implementing theta rhythmicity in the entorhinal-hippocampal network. The SCs also display a robust time-dependent inward rectification in the hyperpolarizing direction that may contribute to the generation of these oscillations. We performed whole cell recordings of SCs in in vitro slices to investigate the specific biophysical and pharmacological properties of the current underlying this inward rectification and to clarify its potential role in the genesis of the subthreshold oscillations. In voltage-clamp conditions, hyperpolarizing voltage steps evoked a slow, noninactivating inward current, which also deactivated slowly on depolarization. This current was identified as I-h because it was resistant to extracellular Ba2+, sensitive to Cs+, completely and selectively abolished by ZD7288, and carried by both Na+ and K+ ions. I-h in the SCs had an activation threshold and reversal potential at approximately -45 and -20 mV, respectively. Its half-activation voltage was -77 mV. Importantly, bath perfusion with ZD7288, but not Ba2+ gradually and completely abolished the subthreshold oscillations, thus directly implicating I-h in their generation. Using experimentally derived biophysical parameters for I-h and the low-threshold persistent Na+ current (I-NaP) present in the SCs, a simplified model of these neurons was constructed and their subthreshold electroresponsiveness simulated. This indicated that the interplay between I-NaP and I-h can sustain persistent subthreshold oscillations in SCs. I-NaP and I-h operate in a push-pull fashion where the delay in the activation/deactivation of I-h gives rise to the oscillatory process.
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| 10. |
- Sanchez, D., Alonso, J. A., Garcia-Hernandez, M., Martinez-Lope,M. J., Martinez J. L., and Mellergård, A.
(author)
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Neutron-diffraction magnetic scattering in ordered and disordered Sr2FeMoO6
- 2002
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In: Appl. Phys.. ; A74, s. 1752-1754
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Journal article (peer-reviewed)
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| 11. |
- Sanchez, D., Alonso, J. A., Garcia-Hernandez, M., Martinez-Lope, M. J., Martinez, J. L., and Mellergård, A.
(author)
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Origin of neutron magnetic scattering in antisite-disordered Sr2 FeMoO6 double perovskites, Modelling of atomic and magnetic structures from powder diffraction data: recent developments of the RMCPOW method
- 2002
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In: Phys. Rev. B. ; 65, s. 104426-
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Journal article (peer-reviewed)
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| 12. |
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| 13. |
- Alonso, Juan, et al.
(author)
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Homological finite derivation type
- 2003. - 1
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In: International Journal of Algebra and Computation. - 0218-1967 .- 1793-6500. ; 13:3, s. 341-359
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Journal article (peer-reviewed)abstract
- In 1987, Squier defined the notion of finite derivation type for a finitely presented monoid. To do this, he associated a 2-complex to the presentation. The monoid then has finite derivation type if, modulo the action of the free monoid ring, the 1-dimensional homotopy of this complex is finitely generated. Cremanns and Otto showed that finite derivation type implies the homological finiteness condition left FP3, and when the monoid is a group, these two properties are equivalent. In this paper we define a new version of finite derivation type, based on homological information, together with an extension of this finite derivation type to higher dimensions, and show connections to homological type FPn for both monoids and groups.
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| 14. |
- Alonso-Vazquez, A, et al.
(author)
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Initial stability of ankle arthrodesis with three-screw fixation. A finite element analysis
- 2004
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In: Clinical Biomechanics. - : Elsevier BV. - 0268-0033. ; 19:7, s. 751-759
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Journal article (peer-reviewed)abstract
- Objective. Compare the initial stability at the fusion site of ankle arthrodesis fixed with two and three screws. Design. Finite element models of ankle arthrodesis were developed from computed tomography images. Two-screw constructs were augmented with a third screw in different orientations and Subjected to loads likely to affect the ankle postoperatively. Background More stable fixation seems to increase the chance of fusion, as it minimises the motion between the tibiotalar interfaces. Methods. Non-linear elastic finite element analyses were performed in external torsion and dorsiflexion. The micromotions at the tibiotalar interface were computed to compare the two- and three-screw fixation in intact and flat-cut arthrodesis. Results. Adding a third screw reduced the micromotions at the fusion site. Inserting the third screw anteriorly predicted lower peak micromotions than inserting the screw posteriorly, except for the intact arthrodesis tested in dorsiflexion. Three-screw intact arthrodesis predicted lower peak micromotions than flat-cut arthrodesis. Conclusions. Better stability was predicted for three-screw ankle arthrodesis. In flat-cut arthrodesis, a third screw inserted anteriorly performed better than a posterior screw. In intact arthrodesis, a posterior screw seemed a better option when flexion stability was the main concern. Even with three-screw fixation, the configuration of the first two-crossed screws may still be important to improve the stability at the fusion site. Relevance The optimal number and placement of screws in ankle arthrodesis has yet to be determined. The differences in stability predicted between various screw configurations and Surface preparation techniques presented here may be the difference between success and failure. (C) 2004 Elsevier Ltd. All rights reserved.
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| 15. |
- Alonso-Vazquez, A, et al.
(author)
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The effect of bone quality on the stability of ankle arthrodesis. A finite element study
- 2004
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In: Foot & Ankle International. - 1944-7876. ; 25:11, s. 840-850
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Journal article (peer-reviewed)abstract
- Background: Despite uniform operating techniques, lack of fusion still occurs after ankle arthrodesis. Differences in the biological healing potential may be a factor but the mechanical performance of the arthrodesis construct because of varying bone quality also may be important. Internal compression techniques are preferred because of higher union rates, shorter fusion times, and fewer complications. A three-screw configuration has been shown to be more stable than a two-screw configuration, but it is not obvious when it should be used. Methods: Three-dimensional finite element models of intact and flat-cut ankle arthrodeses were built, using two and three screws in different configurations. Poor bone quality was simulated by decreasing Young's modulus of the bone. The constructs were loaded in torsion and dorsiflexion, and micromotions at the fusion site were measured. Results: Bone quality had a marked effect on the stability at the arthrodesis site. Inserting two screws at 30 degrees relative to the longitudinal axis of the tibia in an intact arthrodesis seemed the best option, especially as bone quality worsened. The addition of a third screw increased the stability at the arthrodesis site. Conclusions: Overall, intact joint surfaces and three-screw fixation, with the lateral and medial screws inserted produced the most stable arthrodesis constructs when bone quality was poor. Clinical Relevance. Ankle arthrodeses are technically demanding because of the shape and small size of the talus. Preoperative planning is an absolute necessity to determine placement and number of screws. This study shows that poor bone quality decreases the stability of the arthrodesis constructs, suggesting that an attempt should be made to create the most stable three-screw configuration. Finite element models can be used as an effective preoperative tool for planning screw number and placement.
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| 16. |
- Egorov, A. V., et al.
(author)
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Graded persistent activity in entorhinal cortex neurons
- 2002
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 420:6912, s. 173-178
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Journal article (peer-reviewed)abstract
- Working memory represents the ability of the brain to hold externally or internally driven information for relatively short periods of time(1,2). Persistent neuronal activity is the elementary process underlying working memory but its cellular basis remains unknown. The most widely accepted hypothesis is that persistent activity is based on synaptic reverberations in recurrent circuits. The entorhinal cortex in the parahippocampal region is crucially involved in the acquisition, consolidation and retrieval of long-term memory traces for which working memory operations are essential(2). Here we show that individual neurons from layer V of the entorhinal cortex-which link the hippocampus to extensive cortical regions(3)-respond to consecutive stimuli with graded changes in firing frequency that remain stable after each stimulus presentation. In addition, the sustained levels of firing frequency can be either increased or decreased in an input-specific manner. This firing behaviour displays robustness to distractors; it is linked to cholinergic muscarinic receptor activation, and relies on activity-dependent changes of a Ca2+-sensitive cationic current. Such an intrinsic neuronal ability to generate graded persistent activity constitutes an elementary mechanism for working memory.
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| 17. |
- Fransén, Erik, 1962-, et al.
(author)
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Entorhinal neuronal activity during delayed matching tasks may depend upon muscarinic-induced non-specific cation current I(CANM)
- 2001
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In: Neurocomputing. - 0925-2312 .- 1872-8286. ; 38, s. 601-606
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Journal article (peer-reviewed)abstract
- Biophysical compartmental models of stellate, pyramidal-like and interneurons in layer II of the rat entorhinal cortex were used to explore cellular and synaptic components involved in neuronal responses to stimuli in a delayed match to sample (DMS) task. Simulations demonstrate that the muscarinic receptor-induced non-specific cation current, I(CANM), could contribute to these phenomena. Facilitation of I(CANM) by calcium influx during spikes induced by the sample stimulus can cause enhanced responses for matches as well as delay activity. In a network, lateral inhibition can produce match suppression, and in conjunction with stimulus selective/non-selective cells produce non-match enhancement and suppression.
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| 18. |
- Fransén, Erik, 1962-, et al.
(author)
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Ionic mechanisms in the generation of subthreshold oscillations and action potential clustering in entorhinal layer II stellate neurons
- 2004
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 14:3, s. 368-384
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Journal article (peer-reviewed)abstract
- A multi compartmental biophysical model of entorhinal cortex layer II stellate cells was developed to analyze the ionic basis of physiological properties, such as subthreshold membrane potential oscillations, action potential clustering, and the medium afterhyperpolarization. In particular, the simulation illustrates the interaction of the persistent sodium current (I-NaP) and the hyperpolarization activated inward current (I-h) in the generation of subthreshold membrane potential oscillations. The potential role of I-h in contributing to the medium hyperpolarization (mAHP) and rebound spiking was studied. The role of I-h and the slow calcium-activated potassium current I-K(AHP) in action potential clustering was also studied. Representations of I-h and I-NaP were developed with parameters based on voltage-clamp data from whole-cell patch and single channel recordings of stellate cells (Dickson et A, J Neurophysiol 83:2562-2579, 2000; Magistretti and Alonso, J Gen Physiol 114:491-509, 1999; Magistretti et al., J Physiol 521:629-636, 1999a; J Neurosci 19:7334-7341, 1999b). These currents interacted to generate robust subthreshold membrane potentials with amplitude and frequency corresponding to data observed in the whole cell patch recordings. The model was also able to account for effects of pharmacological manipulations, including blockade of I-h with ZD7288, partial blockade with cesium, and the influence of barium on oscillations. In a model with a wider range of currents, the transition from oscillations to single spiking, to spike clustering, and finally tonic firing could be replicated. In agreement with experiment, blockade of calcium channels in the model strongly reduced clustering. In the voltage interval during which no data are available, the model predicts that the slow component of I-h does not follow the fast component down to very short time constants. The model also predicts that the fast component of I-h is responsible for the involvement in the generation of subthreshold oscillations, and the slow component dominates in the generation of spike clusters.
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| 19. |
- Fransén, Erik, 1962-, et al.
(author)
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Simulations of the role of the muscarinic-activated calcium-sensitive nonspecific cation current I-NCM in entorhinal neuronal activity during delayed matching tasks
- 2002
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In: Journal of Neuroscience. - 0270-6474 .- 1529-2401. ; 22:3, s. 1081-1097
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Journal article (peer-reviewed)abstract
- Entorhinal lesions impair performance in delayed matching tasks, and blockade of muscarinic cholinergic receptors also impairs performance in these tasks. Physiological data demonstrate that muscarinic cholinergic receptor stimulation activates intrinsic cellular currents in entorhinal neurons that could underlie the role of entorhinal cortex in performance of these tasks. Here we use a network biophysical simulation of the entorhinal cortex to demonstrate the potential role of this cellular mechanism in the behavioral tasks. Simulations demonstrate how the muscarinic-activated calcium-sensitive nonspecific cation current I-NCM could provide a cellular mechanism for features of the neuronal activity observed during performance of delayed matching tasks. In particular, I-NCM could underlie (1) the maintenance of sustained spiking activity during the delay period, (2) the enhancement of spiking activity during the matching period relative to the sample period, and (3) the resistance of sustained activity to distractors. Simulation of a larger entorhinal network with connectivity chosen randomly within constraints on number, distribution, and weight demonstrates appearance of other phenomena observed in unit recordings from awake animals, including match suppression, non-match enhancement, and non-match suppression.
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| 20. |
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| 21. |
- Hasselmo, M. E., et al.
(author)
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Computational modeling of entorhinal cortex
- 2000
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In: PARAHIPPOCAMPAL REGION. - NEW YORK : New York Academy of Sciences. - 1573312630 ; , s. 418-446
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Conference paper (peer-reviewed)abstract
- Computational modeling provides a means for linking the physiological and anatomical characteristics of entorhinal cortex at a cellular level to the functional role of this region in behavior. We have developed detailed simulations of entorhinal cortical neurons and networks, with an emphasis on the role of acetylcholine in entorhinal cortical function. Computational modeling suggests that when acetylcholine levels are high, this sets appropriate dynamics for the storage of stimuli during performance of delayed matching tasks. In particular, acetylcholine activates a calcium-sensitive nonspecific cation current which provides an intrinsic cellular mechanism which could maintain neuronal activity across a delay period. Simulations demonstrate how this phenomena could underlie entorhinal cortex delay activity as described in previous unit recordings. Acetylcholine also induces theta rhythm oscillations which may be appropriate for timing of afferent input to be encoded in hippocampus and for extraction of individual stored sequences from multiple stored sequences. Lower levels of acetylcholine may allow sharp wave dynamics which can reactivate associations encoded in hippocampus and drive the formation of additional traces in hippocampus and entorhinal cortex during consolidation.
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| 25. |
- Ojeda, M., et al.
(author)
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Synthesis of Rh nano-particles by the microemulsion technology - Particle size effect on the CO+H-2 reaction
- 2004
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In: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 274:1-2, s. 33-41
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Journal article (peer-reviewed)abstract
- Several alumina-supported rhodium-based catalysts have been prepared using the microemulsion technology. The change of microemulsion properties led to catalysts with different Rh particle size and narrow size distribution while keeping the same metal loading. The metal particle size was determined by XRD and TEM. These catalysts were tested in the CO hydrogenation reaction in order to investigate the influence of the Rh particle size. The catalytic results indicated that turnover frequency (TOF) increased about four times when the Rh particle size increased approximately from
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