Fluidal pyroclasts reveal the intensity of peralkaline rhyolite pumice cone eruptions.

Peralkaline rhyolites are medium to low viscosity, volatile-rich magmas typically associated with rift zones and extensional settings. The dynamics of peralkaline rhyolite eruptions remain elusive with no direct observations recorded, significantly hindering the assessment of hazard and risk. Here we describe uniquely-preserved, fluidal-shaped pyroclasts found within pumice cone deposits at Aluto, a peralkaline rhyolite caldera in the Main Ethiopian Rift. We use a combination of field-observations, geochemistry, X-ray computed microtomography (XCT) and thermal-modelling to investigate how these pyroclasts are formed. We find that they deform during flight and, depending on size, quench prior to deposition or continue to inflate then quench in-situ. These findings reveal important characteristics of the eruptions that gave rise to them: that despite the relatively low viscosity of these magmas, and similarities to basaltic scoria-cone deposits, moderate to intense, unstable, eruption columns are developed; meaning that such eruptions can generate extensive tephra-fall and pyroclastic density currents.

Textural and geochemical constraints on andesitic plug emplacement prior to the 2004-2010 vulcanian explosions at Galeras volcano, Colombia.

Hazardous sequences of vulcanian explosions are thought to result from the repeated emplacement and destruction of degassed, highly crystalline magma plugs in the shallow conduit of arc volcanoes. The processes governing the timing and magnitude of these explosions are thought to be related to magma ascent rate and efficiency of degassing and crystallisation. We study a rare suite of time-constrained ballistic bombs from the 2004-2010 period of activity of Galeras volcano to reconstruct magma plug architecture prior to six individual vulcanian explosions. We find that each plug was vertically stratified with respect to crystallinity, vesicularity and melt volatile content, melt composition and viscosity. We interpret this structure as resulting from multiple bubble nucleation events and degassing-driven crystallisation during multi-step ascent of the magma forming the plug, followed by spatially variable crystallisation within the plug under contrasting conditions of effective undercooling created by degassing. We propose that the shallow conduit evolved from more open degassing conditions during 2004-2008 to more closed conditions during 2009-2010. This resulted in explosions becoming smaller and less frequent over time during 2004-2008, then larger and more frequent over time during 2009-2010. This evolution was controlled by changing average ascent rates and is recorded by systematic changes in plagioclase microlite textures. Our results suggest that small volume vulcanian explosions (~ 105 m3) should generally be associated with longer repose times (hundreds of days) and produce ballistics characterised by small numbers of large, prismatic plagioclase microlites. Larger volume vulcanian explosions (~ 106 m3) should be associated with shorter repose times (tens of days) and produce ballistics characterised by high numbers of small, more tabular plagioclase microlites.

Crystal and melt inclusion timescales reveal the evolution of magma migration before eruption.

Volatile element concentrations measured in melt inclusions are a key tool used to understand magma migration and degassing, although their original values may be affected by different re-equilibration processes. Additionally, the inclusion-bearing crystals can have a wide range of origins and ages, further complicating the interpretation of magmatic processes. To clarify some of these issues, here we combined olivine diffusion chronometry and melt inclusion data from the 2008 eruption of Llaima volcano (Chile). We found that magma intrusion occurred about 4 years before the eruption at a minimum depth of approximately 8 km. Magma migration and reaction became shallower with time, and about 6 months before the eruption magma reached 3-4 km depth. This can be linked to reported seismicity and ash emissions. Although some ambiguities of interpretation still remain, crystal zoning and melt inclusion studies allow a more complete understanding of magma ascent, degassing, and volcano monitoring data.

Identifying Connectome Module Patterns via New Balanced Multi-Graph Normalized Cut.

Computational tools for the analysis of complex biological networks are lacking in human connectome research. Especially, how to discover the brain network patterns shared by a group of subjects is a challenging computational neuroscience problem. Although some single graph clustering methods can be extended to solve the multi-graph cases, the discovered network patterns are often imbalanced, e.g. isolated points. To address these problems, we propose a novel indicator constrained and balanced multi-graph normalized cut method to identify the connectome module patterns from the connectivity brain networks of the targeted subject group. We evaluated our method by analyzing the weighted fiber connectivity networks.

Is ultrasound guidance superior to conventional nerve stimulation for coracoid infraclavicular brachial plexus block?

BACKGROUND AND OBJECTIVES: In different peripheral nerve blocks, it has been speculated that needle guidance by ultrasound improves onset time and success rate compared with the more frequently used nerve stimulation-guided technique. In the present study, we tested the hypothesis that ultrasound guidance improves onset time of coracoid infraclavicular brachial plexus block (IBPB) when compared with a nerve stimulation-guided technique. METHODS: Seventy patients scheduled for hand or forearm surgery were randomly assigned to receive coracoid IBPB using either ultrasound guidance (group U, n = 35), or nerve stimulation (group S, n = 35). Patients were assessed for sensory and motor block every 5 mins after injection of local anesthetic. Onset time, the primary end point, was defined as the time required for complete sensory and motor block. Time required to perform the block, success rate, and time to resolution of motor blockade were also recorded (secondary end points). RESULTS: Onset of complete sensory and motor blockade was similar in the 2 groups (17 mins [8 mins] in group U and 19 mins [8 mins] in group S; P = 0.321). Time required to perform the block was shorter in group U (3 mins [1 min]) as compared with group S (6 mins [2 mins]; P < 0.0001). No differences were observed in success rate (89% in group U and 91% in group S; P = 0.881) and time to resolution of motor blockade (237 mins [45 mins] in group U and 247 mins [57 mins] in group S; P = 0.418). CONCLUSIONS: The present investigation demonstrates that ultrasound guidance and nerve stimulation provide similar onset time, success rate, and duration of motor blockade for coracoid IBPB; however, ultrasound guidance reduces the time required to perform the block.

Comparison of continuous infusion versus automated bolus for postoperative patient-controlled analgesia with popliteal sciatic nerve catheters.

BACKGROUND: This investigation was designed to compare a new methodology of automated regular bolus with a continuous infusion of local anesthetic for continuous popliteal sciatic block; both regimens were combined with patient-controlled analgesia (PCA). METHODS: Fifty patients undergoing hallux valgus repair were randomly allocated to receive an infusion of 0.125% levobupivacaine administered through a popliteal catheter as an automated regular bolus (n = 25) or as a continuous infusion (n = 25), both combined with PCA. Postoperative pain scores, incremental doses delivered by the PCA, local anesthetic consumed per hour, and the need for rescue tramadol analgesia were recorded. RESULTS: Both dosing regimens provided similar postoperative analgesia. Consumption of local anesthetic (5.14 ml/h, 5-5.75 ml/h) and dose request from the PCA (1, 0-5.4) was lower in the automated bolus group as compared to the continuous infusion group (5.9 ml/h, 5.05-7.8 ml/h; doses by PCA: 6.5, 0-20.5; P < 0.05). The need for rescue tramadol was similar in the two groups. CONCLUSION: In continuous popliteal sciatic block, local anesthetic administered as an automated regular bolus in conjunction with PCA provided similar pain relief as a continuous infusion technique combined with PCA; however, the new dosing regimen reduced the need for additional PCA and the overall consumption of local anesthetic.

Low volume and high concentration of local anesthetic is more efficacious than high volume and low concentration in Labat's sciatic nerve block: a prospective, randomized comparison.

BACKGROUND: Various factors markedly affect the onset time and success rate, of peripheral nerve blockade. This prospective, randomized, double-blind study, compared a dose of mepivacaine 300 mg, in a 20 or 30 mL injection volume for sciatic nerve blockade using Labat's posterior approach. METHODS: A total of 90 patients undergoing foot surgery were randomly allocated to receive sciatic nerve block with 20 mL of 1.5% mepivacaine (n = 45) or 30 mL of 1% mepivacaine (n = 45). All blocks were performed with the use of a nerve stimulator (stimulation frequency 2 Hz; intensity 1.5-0.5 mA). In the two groups, appropriate nerve stimulation was elicited at <0.5 mA and the targeted evoked motor response was plantar flexion of the foot. Time required for onset of sensory and motor block in the distribution of the tibial and common peroneal nerves were recorded. A successful block was defined as a complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot. RESULTS: A greater success rate was observed with 20 mL of 1.5% mepivacaine (96.6%) than with 30 mL of 1% mepivacaine (68.9%; P < 0.05). Time to onset of complete sensory and motor block was shorter after injection of 20 mL of 1.5% mepivacaine (11 +/- 6 min and 13 +/- 7 min, respectively) than after 30 mL of 1% mepivacaine (17 +/- 8 min and 19 +/- 8 min, respectively, P < 0.05). CONCLUSION: In Labat's sciatic nerve blockade, administering a low volume and a high concentration of local anesthetic (1.5% mepivacaine) is associated with a higher success rate and a shorter onset time than a high volume and a low concentration of solution (1% mepivacaine).

A "new" automated bolus technique for continuous popliteal block: a prospective, randomized comparison with a continuous infusion technique.

BACKGROUND: We designed the present, prospective, randomized, double-blind study to compare the administration of an automated intermittent bolus dose with a conventional technique of continuous infusion of local anesthetic for postoperative analgesia in continuous popliteal sciatic nerve blockade. METHODS: Forty-four patients undergoing hallux valgus repair were randomly assigned to receive either a continuous infusion of 0.125% levobupivacaine with an infusion rate of 5 mL/h (continuous infusion group, n=22) or automated bolus doses of 5 mL every hour of the same local anesthetic (automated bolus group, n=22) for 24 h. Postoperative pain scores were assessed using a verbal rating pain score. The amount of rescue tramadol medication for pain was also recorded. RESULTS: In patients of the automated bolus group there was a reduction in pain scores (P<0.05) during the postoperative period, when compared to patients of the continuous infusion group. Five patients in the automated bolus group (24%) and 11 patients of the continuous group (52%) required rescue tramadol analgesia (P=0.055). CONCLUSION: The present investigation demonstrated that local anesthetic administered by an automated bolus technique provided better postoperative pain relief than a continuous infusion technique for continuous popliteal nerve block after foot surgery.

Interpretation of the experimental data on the reduction reaction of NO by CO on rhodium by Monte Carlo simulations and by solving the kinetic equations of the reaction mechanism.

Some mechanisms of the reduction reaction of NO by CO on rhodium are analyzed and discussed, solving the kinetics equations and using Monte Carlo simulations, in terms of its ability to interpret the recent experiments of Zaera et al., who used a molecular beam method to study experimentally the kinetics of the reaction. Critical use is also made of the information on rate constants available for this system in the literature. Uniform catalytic surfaces and the statistical incipient percolation cluster (IPC) fractal are considered in the simulations.

Apical suction leads to severe ischemia of the ventricular apex.

OBJECTIVE: Apical suction devices allow displacement of the heart in off-pump coronary artery surgery. However, high vacuum pressure may injure the suctioned myocardium. It has been demonstrated that partial pressure of oxygen in the myocardium (ptiO(2)) is a sensitive and rapid indicator of myocardial ischemia. The purpose of this study is to evaluate the effect of apical suction on the ptiO(2) as an indirect measure of myocardial perfusion of the ventricular apex. METHODS: Twenty-six patients undergoing elective off-pump coronary surgery were studied. Intramyocardial ptiO(2) was continuously measured using a flexible catheter microprobe (Licox GMS mbH, Kiel, Germany). Patients were divided into two groups. In one group (Group A; n=14), the microprobe was intraoperatively inserted into the myocardium of the left ventricular apex. In the second group (Group B; n=12), the probe was inserted in the anterior wall of the left ventricle. Intramyocardial ptiO(2) monitoring was made with the heart in the resting position and after placing the apical suction device. RESULTS: In Group A, basal ptiO(2) was 15.3+/-7.4 mmHg. One minute after placing the apical suction device, the ptiO(2) significantly decreased to 2.3+/-1 mmHg (p<0.001). A progressive increase of ptiO(2) was observed immediately after the Xpose suction device was removed. ptiO(2) was 13.6+/-9.1 mmHg 5 min after releasing the suction cup and increased to 27.2+/-12.6 mmHg 20 min later. In Group B, basal ptiO(2) was 17+/-10.3 mmHg. No significant changes were observed in Group B after placing and removing the suction cup. CONCLUSIONS: Apical suction devices lead to severe ischemia of the suctioned myocardium. Collapse of coronary vessels due to vacuum pressure is a possible mechanism. Reperfusion occurs immediately after removing the suction cup and a significant reactive hyperemia is observed.

Pituitary adenylate cyclase-activating peptide/vasoactive intestinal peptide receptors in human normal mammary gland and breast cancer tissue.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) bind similarly to VPAC1 and VPAC2 receptors, whereas PACAP binds with higher affinity than VIP to PAC1 receptors. Here we demonstrate by different approaches the expression of the three subclasses of PACAP/VIP receptors in human normal and malignant breast tissue. At the mRNA level, reverse transcription-polymerase chain reaction experiments showed VPAC1 and VPAC2 receptors as well as various isoforms (null, hip/hop) of PAC1 receptors due to alternative splicing. At the protein level, Western blot experiments revealed the three subclasses of receptor although no conclusive differences could be established when comparing control, peritumoral and tumoral tissue samples. Immunohistochemistry showed the distribution of these receptors: they were located at epithelial cells in normal and cancer conditions but also in leukocytes at the stromal level in carcinomatous tissue. A weaker immunostaining of PAC1 receptors in normal tissue and a strong density of the three PACAP/VIP receptor subclasses in cancer tissue may be related to differential expression patterns during breast tumor progression but more samples need to be studied to validate this hypothesis. PAC1, VPAC1 and VPAC2 receptors were functional, as shown by their coupling to adenylate cyclase stimulation: VIP, PACAP-27 and PACAP-38 behaved similarly at this level, whereas both VPAC receptors acted alike as shown by means of specific peptide agonists and antagonists. The present results together with the known presence of PACAP and VIP in the mammary gland support a paracrine/autocrine involvement of both peptides at this level in physiological and pathological conditions, i.e. during malignant transformation.

Monte Carlo studies of the dynamic behavior of the reduction reaction of NO by CO over a surface of clusters supported on a fractal.

A Monte Carlo simulation study is made of the dynamic behavior of the reduction reaction of NO by CO, assuming an experimentally representative mechanism, over a catalytic substrate consisting of clusters of active sites supported on a fractal. Various empirical laws are found for the evolution in time of production over various cyclic graphs or trees that represent the various clusters of catalytic sites on the surface. An analysis is made of the phase diagrams and the production achieved versus concentration of the gas phase at different temperatures.

Plantar flexion seems more reliable than dorsiflexion with Labat's sciatic nerve block: a prospective, randomized comparison.

Labat's classic approach to the sciatic nerve has not been able to show which motor response of the foot provides a more frequent rate of complete sensory and motor block. In this prospective, randomized, double-blind study, we compared plantar flexion with dorsiflexion with regard to onset time and efficacy of sciatic nerve block using the classic posterior approach. A total of 80 patients undergoing hallux valgus repair were randomly allocated to receive sciatic nerve block after evoked plantar flexion (n=40) or dorsiflexion (n=40). Twenty milliliters of 0.75% ropivacaine was injected after the motor response was elicited at <0.5 mA. Success rate was defined as complete sensory and motor block in all sciatic nerve distributions associated with a pain-free surgery. Time required for onset of sensory and motor block of the foot was recorded. Success was more frequent after elicited plantar flexion (87.5%) than dorsiflexion (55%; P <0.05). Onset of complete sensory and motor block of the foot was faster after elicited plantar flexion (10 +/- 10 min and 13 +/- 10 min, respectively) compared with dorsiflexion (20 +/- 11 min and 24 +/- 12 min; P <0.05). We conclude that plantar flexion of the foot predicts a shorter onset time and a more frequent success rate than dorsiflexion with Labat's classic posterior sciatic nerve block.

Sciatic nerve block via posterior Labat approach is more efficient than lateral popliteal approach using a double-injection technique: a prospective, randomized comparison.

BACKGROUND: For peripheral nerve blockade, the double-injection technique proved to be superior to a single injection in previous investigations. The current study was designed to compare onset time and efficacy of two different double-injection approaches for sciatic nerve block with 0.75% ropivacaine. METHODS: A total of 50 patients undergoing foot surgery were randomly assigned to receive sciatic nerve blockade by means of the classic (Labat) posterior approach (n = 25) or a lateral popliteal approach (n = 25). All blocks were performed with the use of a nerve stimulator, and both major components of the sciatic nerve (tibial and common peroneal nerves) received separately 10 ml ropivacaine, 0.75%. Success rate was defined as a complete sensory and motor block associated with pain-free surgery. RESULTS: A greater success rate was observed in the classic group (96%) as compared with the popliteal group (68%; P < 0.05). A general anesthetic became necessary in six patients (24%) with the lateral popliteal approach and none with the classic approach (P < 0.05). The onset of complete sensory and motor blockade was significantly faster in the classic group (12 +/- 6 min) as compared with the popliteal group (26 +/- 10 min; P < 0.05). CONCLUSION: A double injection with a relatively low volume of 0.75% ropivacaine generated a higher success rate and a shorter onset time of sensory and motor blockade after the classic Labat approach than after a lateral popliteal approach.

PACAP expression and distribution in human breast cancer and healthy tissue.

Pituitary adenylate cyclase-activating peptide (PACAP) is involved in various biological processes including cell growth, proliferation and differentiation. Here, we demonstrate for the first time the presence of both PACAP mRNA and PACAP immunoreactivity in human normal breast and breast carcinoma. Control, peritumoral and tumoral tissue pieces expressed preproPACAP mRNA since reverse transcription-polymerase chain reaction analysis gave an amplification product of the expected size (226 bp), which was further identified by analysis of the sequence. A main 19.9-kDa product (preproPACAP protein) was identified by Western blot in the three classes of breast tissue together with a small amount of a 14.6-kDa product (conceivably a result of partial processing by proprotein convertases). However, the mature peptide PACAP-38 was absent. The levels of both PACAP mRNA and PACAP immunoreactivity increased from normal to peritumoral and tumoral breast tissues but more patients must be considered to reinforce this feature. Immunohistochemistry showed the localization of PACAP immunoreactivity in alveolar epithelial cells in normal and carcinomatous tissues but also, at high density, in duct-like structures and in leucocytes in the connective tissue from breast cancer pieces. The results suggest that PACAP may play a role by autocrine/paracrine mechanisms in both normal human breast physiology and breast tumorigenesis.

Luteinizing hormone-releasing hormone antagonist Cetrorelix regulates the expression of Galphas and Galphai protein subunits and adenylate cyclase activity in rat ovary, breast and pituitary.

The mechanisms by which luteinizing hormone-releasing hormone (LH-RH) antagonists act on extra-pituitary tissues are poorly understood. In view of extensive use of Cetrorelix in gynecology and oncology, we investigated its effects on signal transduction pathways of G-protein coupled receptors and adenylate cyclase which are involved in a huge array of cellular events including normal and pathological cell proliferation. Thirty days after a single i.m. injection of 3 mg Cetrorelix pamoate depot to female rats, normal or ovariectomized, we evaluated the effects of this chronic treatment on the expression of alphas and alphai G-protein subunits in the ovary, breast and pituitary, as well as the adenylate cyclase response in vitro to LH-RH, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP). Varied patterns of response to Cetrorelix, depending on the gland and estrogenic status were observed. Western blot analysis showed a modest decrease of alphas and a modest increase of alphai G-protein subunit levels in ovary, a marked increase of alphas and alphai levels in breast, and a lack of effect on alphas/alphai levels in pituitary. In the ovary, adenylate cyclase activity was not changed by in vitro addition of LH-RH, but the responses to VIP and PACAP increased after Cetrorelix treatment. In the breast, chronic administration of the LH-RH antagonist decreased the adenylate cyclase response to PACAP, which returned to normal after ovariectomy. In the pituitary, Cetrorelix abolished the stimulatory effect of VIP upon adenylate cyclase activity. Thus, the LH-RH antagonist Cetrorelix exerted selective modifications at different steps of the G-protein coupled receptors/adenylate cyclase system of signal transduction in the rat ovary, breast and pituitary.

The effects of three different approaches on the onset time of sciatic nerve blocks with 0.75% ropivacaine.

UNLABELLED: We studied three different injection techniques of sciatic nerve block in terms of block onset time and efficacy with 0.75% ropivacaine. A total of 75 patients undergoing foot surgery were randomly allocated to receive sciatic nerve blockade by means of the classic posterior approach (group classic; n = 25), a modified subgluteus posterior approach (group subgluteus; n = 25), or a lateral popliteal approach (group popliteal; n = 25). All blocks were performed with the use of a nerve stimulator (stimulation frequency, 2 Hz; intensity, 2-0.5 mA) and 30 mL of 0.75% ropivacaine. Onset of nerve block was defined as complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot. In the three groups, an appropriate sciatic stimulation was elicited at <0.5 mA. The failure rate was similar in the three groups (group popliteal: 4% versus group classic: 4% versus group subgluteus: 8%). The onset of nerve block was slower in group popliteal (25 +/- 5 min) compared with group classic (16 +/- 4 min) and group subgluteus (17 +/- 4 min; P < 0.001). There was no significant difference in the onset of nerve block between group classic and group subgluteus. No differences in the degree of pain measured at the first postoperative administration of pain medication were observed among the three groups. We conclude that the three approaches resulted in clinically acceptable anesthesia in the distribution of the sciatic nerve. The subgluteus and classic posterior approaches generated a significantly faster onset of anesthesia than the lateral popliteal approach. IMPLICATIONS: Comparing three different approaches to the sciatic nerve with 0.75% ropivacaine, the classic and subgluteal approaches exhibited a faster onset time of sensory and motor blockade than the lateral popliteal approach.

Lateral approach to the sciatic nerve in the popliteal fossa: a comparison between 1.5% mepivacaine and 0.75% ropivacaine.

BACKGROUND AND OBJECTIVES: Ropivacaine and mepivacaine are commonly used local anesthetics for peripheral nerve blockade. The purpose of the present study was to compare onset time, quality of anesthesia, and duration of analgesia with ropivacaine 0.75% and mepivacaine 1.5% for lateral popliteal nerve block. METHODS: Fifty American Society of Anesthesiologists (ASA) physical status I or II patients scheduled for foot and ankle surgery with calf tourniquet under lateral popliteal sciatic nerve block were randomly assigned to receive 30 mL of either ropivacaine 0.75% or mepivacaine 1.5%. Time required for onset of sensory and motor block, resolution of motor blockade, onset of postsurgical pain, and time of first analgesic medication were recorded. RESULTS: The 2 groups were similar with regard to demographic variables and duration of surgery. Onset of sensory and motor block was significantly shorter in the mepivacaine group (9.9 +/- 3.3 min and 14.7 +/- 3.6 min, respectively) than in the ropivacaine group (18.1 +/- 6.1 min and 23.6 +/- 5.5 min, respectively) (P < 0.001). Resolution of motor block occurred later in the ropivacaine group than in the mepivacaine group (P < 0.001), and duration of postoperative analgesia was significantly longer in the ropivacaine group (19 +/- 3.4 h) compared with the mepivacaine group (5.9 +/- 1.1 h) (P < 0.001). Analgesic requirements were higher in mepivacaine group than in the ropivacaine group (P < 0.001). There were 2 failed blocks, one in each group. CONCLUSIONS: Both ropivacaine and mepivacaine provided effective sciatic nerve blockade. Mepivacaine 1.5% displayed a significantly shorter onset time than ropivacaine 0.75%. Postoperatively, ropivacaine 0.75% resulted in longer-lasting analgesia and less need for oral pain medication.

Structural effects in the kinetic behavior of the monomer-dimer surface reaction over nondeterministic fractal surfaces.

A study is made of the segregation effect of adsorbed species related to the inner structure of two bidimensional adsorbent fractals, the incipient percolation cluster (IPC) and the backbone of the IPC, and their connection with the rate-determining step of the kinetic mechanism of the monomer-dimer (MD) surface reaction on those fractals. Production, R(AB), is proportional to the concentration of A in the gas phase y(A) and to the fraction of vacant superficial sites x(E) (R(AB)=y(A)x(E)), and it is shown that adsorption of the monomer is the rate-controlling step of the reaction mechanism.

Brosilow-Ziff model for the CO-NO surface reaction on disordered two- and three-dimensional substrates.

The Brosilow-Ziff model, which for a uniform lattice shows superficial poisoning by the "checkerboard mechanism" for simplified Langmuir-Hinshelwood kinetics of the reduction reaction of NO by CO, has been studied in the case of various disordered substrates: two-dimensional (2D) incipient percolation cluster, backbone, and diffusion-limited aggregate (2D) fractals, together with a deterministic fractal and a statistical substrate, both three-dimensional. Some additional effects such as diffusion, nearest-next-neighbor sites, and desorption are also considered. The systems were found to be nonreactive and pseudoreactive in all the cases which showed the checkerboard mechanism. Otherwise, a reactive zone (window) related directly to the geometric structure of the substrate is seen.