Effects of Visual Cues of Object Density on Perception and Anticipatory Control of Dexterous Manipulation

Anticipatory force planning during grasping is based on visual cues about the object’s physical properties and sensorimotor memories of previous actions with grasped objects. Vision can be used to estimate object mass based on the object size to identify and recall sensorimotor memories of previously manipulated objects. It is not known whether subjects can use density cues to identify the object’s center of mass (CM) and create compensatory moments in an anticipatory fashion during initial object lifts to prevent tilt. We asked subjects (n = 8) to estimate CM location of visually symmetric objects of uniform densities (plastic or brass, symmetric CM) and non-uniform densities (mixture of plastic and brass, asymmetric CM). We then asked whether subjects can use density cues to scale fingertip forces when lifting the visually symmetric objects of uniform and non-uniform densities. Subjects were able to accurately estimate an object’s center of mass based on visual density cues. When the mass distribution was uniform, subjects could scale their fingertip forces in an anticipatory fashion based on the estimation. However, despite their ability to explicitly estimate CM location when object density was non-uniform, subjects were unable to scale their fingertip forces to create a compensatory moment and prevent tilt on initial lifts. Hefting object parts in the hand before the experiment did not affect this ability. This suggests a dichotomy between the ability to accurately identify the object’s CM location for objects with non-uniform density cues and the ability to utilize this information to correctly scale their fingertip forces. These results are discussed in the context of possible neural mechanisms underlying sensorimotor integration linking visual cues and anticipatory control of grasping

Influence of Water Vapour on Low-temperature CO Oxidation over Au/Fe2O3 Catalyst

Influence of water vapour on the activity of Au/Fe2O3 catalyst was tested in the reaction of low-temperature CO oxidation. Addition of water vapour had a positive influence in the temperature range from 303 K to 383 K. In situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) and FT-IR measurements in a vacuum showed the importance of water and –OH groups, as water-derived species, for the efficiency of the catalyst in low-temperature oxidation of CO

Behavior of the resonant absorption area of a 57Fe-doped Ni/C catalyst during sulfidation

In-situ Moessbauer spectroscopy measurements down to 4.2 K were performed on a 57Fe-doped Ni/C catalyst after various successive sulfidation treatments. After exposure of the catalysts to the H2S/H2 gas mixt. at room temp., part of the 57Fe becomes sulfidic. The rest is present as a sulfate-like intermediate species. The interaction between this intermediate species and the carbon support material is influenced by water. A

Mössbauer emission study on 57Co doped carbon-supported Ni and Ni-Mo sulfide hydrotreating catalysts : the influence of phosphorus on the structure

In the present study it is demonstrated that Mössbauer emission spectroscopy (MES) can generate information on the various Ni phases present in sulfided Ni containing catalysts when a small amount of 57Co is used as a probe for Ni.Application of MES to 57Co:Ni(4.5)Mo(8.0)/C and 57Co:Ni(5.6)/C revealed the formation of a so-called "Ni-Mo-S" phase in the former and a bulk sulfide in the latter catalyst. After addition of phosphorus a "Ni-(thio)phosphate" phase is found to be formed in both catalysts.The relation between the structure of these catalysts and their activity for thiophene HDS and quinoline HDN is discussed

So-called "Co-Mo-S" phase observed in carbon-supported cobalt sulfide catalyst by Mössbauer emission spectroscopy

No abstract

Sulfidation and activity of Co/C catalysts having extremely low cobalt-loading: A Moessbauer emission spectroscopy and thiophene hydrodesulfurization study

Up to a sulfiding temp. of 473 K, the behavior of Co/C catalysts with extremely low cobalt loadings (ppm range) agrees with the trend obsd. before in the Moessbauer emission spectroscopy (MES) spectra of Co/C catalysts with much higher cobalt loadings (0.04-43. wt.%). Sulfiding at 573 K results in a rather well-defined very highly dispersed (most likely monatomically) Co sulfide species which shows a doublet with the extremely large value Q.S. = 4.11 mm/s. In this species the cobalt atoms may be four-fold (square-planar) or five-fold (square-pyramid) coordinated by sulfur. Sulfiding at 673 K results in the disappearance of this highly dispersed Co sulfide species and the newly formed species are again similar to the one previously found for Co/C catalysts with higher cobalt loadings. This finally formed Co sulfide species does not exhibit the Co-Mo-S MES spectrum (Q.S. between 1.0 and 1.3 mm/s) whereas its intrinsic thiophene hydrodesulfurization (HDS) activity equals that of cobalt in the Co-Mo-S phase. Thus, there is no general relation between the thiophene HDS activity (measured at atm. pressure) and the amt. of cobalt exhibiting a Co-Mo-S MES spectrum. [on SciFinder (R)

Sulfidation of carbon-supported iron-molybdemum oxide catalysts

Carbon-supported iron-molybdenum sulphide catalysts were characterized by means of Mössbauer spectroscopy at temperatures down to 4.2 K. Thiophene hydrodesulphurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The molybdenum content was 9.5 wt.-% whereas the iron content varied from 0.6 to 9.0 wt.-%. Sequential deposition (Molybdenum first) by pore-volume impregnation was employed to prepare oxidic catalyst precursors. The oxidic catalyst precursors were dried at 293 K in an air flow, followed by an additional hydrogen treatment up to 393 K. The type and relative particle sizes of the iron compounds present in the oxidic precursors and in the sulphided and reoxidized catalysts were determined by Mössbauer spectroscopy. It was demonstrated that after sulphidation for 4 h at 623 K, the composition of the sulphide catalyst depends on the iron content. Sulphided Fe-Mo/C catalysts contain a mixed "FeMoS" phase and "Fe-sulphide". The former is responsible for the observed promoting effect toward thiophene HDS. From the temperature dependence of the resonant absorption areas, it was concluded that the iron atoms in the "FeMoS" phase are located at the surface of MoS2 microcrystals. The amount of "Fe-sulphide" present in the catalyst was found to increase with increasing iron content. This "Fe-sulphide" might partly cover the "FeMoS" phase, thus causing a decrease in the promoting effect

An EXAFS study on the so-called "Co-Mo-S" phase in Co/C and CoMo/c, compared with a Mössbauer emission spectroscopy study

EXAFS measurements were performed on four sulfided catalysts with the same compn. as their 57Co-contg. counterparts which were previously characterized by Moessbauer emission spectroscopy. The Co species in Co/C catalysts with a Co-Mo-S-like Moessbauer emission spectrum after sulfidation at 373 K is similar to the species with the Co-Mo-S spectrum in CoMo/C catalysts. In both cases the Co atoms are present in a very highly dispersed Co species. In the catalyst without Mo this sulfidic Co species strongly sinters during sulfidation at 673 K, resulting in a Co9S8-type phase. In the CoMo/C catalyst, the Mo hinders sintering of the Co species. [on SciFinder (R)

Sulfidation of carbon-supported iron-molybdemum oxide catalysts

Carbon-supported iron-molybdenum sulphide catalysts were characterized by means of Mössbauer spectroscopy at temperatures down to 4.2 K. Thiophene hydrodesulphurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The molybdenum content was 9.5 wt.-% whereas the iron content varied from 0.6 to 9.0 wt.-%. Sequential deposition (Molybdenum first) by pore-volume impregnation was employed to prepare oxidic catalyst precursors. The oxidic catalyst precursors were dried at 293 K in an air flow, followed by an additional hydrogen treatment up to 393 K. The type and relative particle sizes of the iron compounds present in the oxidic precursors and in the sulphided and reoxidized catalysts were determined by Mössbauer spectroscopy. It was demonstrated that after sulphidation for 4 h at 623 K, the composition of the sulphide catalyst depends on the iron content. Sulphided Fe-Mo/C catalysts contain a mixed "FeMoS" phase and "Fe-sulphide". The former is responsible for the observed promoting effect toward thiophene HDS. From the temperature dependence of the resonant absorption areas, it was concluded that the iron atoms in the "FeMoS" phase are located at the surface of MoS2 microcrystals. The amount of "Fe-sulphide" present in the catalyst was found to increase with increasing iron content. This "Fe-sulphide" might partly cover the "FeMoS" phase, thus causing a decrease in the promoting effect