Two Models for K-12 Hypermediated Earth System Science Lessons Based on Internet Resources

An immense collection of daily and archived earth and space science digital images and database information sources are readily accessible to K-12 teachers through the Internet and the World Wide Web. However, these abundant electronic resources are designed for scientists and often need to be modified to benefit students. Advances in hypermedia as an instructional tool for earth system science education provide a mechanism for designing user-friendly and structured classroom units based on this available data. Two models proposed as a foundation for materials development are the Learning Cycle Model and the Investigation/Experimentation Model. A high demand for Internet-based curricular materials development to take advantage of the current technology suggests an educational research agenda to determine which lesson formats are most effective for learners.     

The Properties of a cellulolytic microbial community growing on pure cellulose and lignocellulose

A microbial community capable of degrading pure cellulose has been isolated from soil using a continuous flow chemostat. The component organisms have been identified as Penicillium nigricans, Paecilomyces liliacinus, Fusarium oxysporum (3 strains), Aspergillus fumigatus, Gliocladium roseum, and Penicillium simplicissimum. Extracellular enzyme production (exoglucanase, endoglucanase, and (Β-glucosidase) and cellulose breakdown by the whole community and the component organisms in pure culture was measured during growth on pure cellulose in batch culture. After 30 d, 50–60% degradation was achieved by Penicillium simplicissimum, Aspergillus fumigatus, and the mixed culture. These cultures also produced the highest levels of extracellular endo- and exoglucanase and were able to produce the full enzyme complex necessary for the degradation of crystalline cellulose. The other isolates were capable of 0–20% degradation and produced lower levels of enzyme activity. Most were unable to produce the full enzyme complex. The results indicated that the whole community was no better at degrading pure cellulose than two members in pure culture. Since the full potential of the community may not be expressed on pure cellulose, breakdown and enzyme production was investigated during growth on lignocellulose. A large proportion of lignocellulosic material consists of xylan and enzymes capable of degrading this component were investigated. The highest percentage degradation and enzyme production (with the exception of Β-glucosidase) after 15 d growth on straw was achieved by the same three cultures. Studies of their growth on hay and straw were extended over a 60-d period. The rate and extent of degradation of hay by P. simplicissimum and A. fumigatus was similar to that of the mixed culture, more than 40% degradation occurring in 40 d. However, differences in levels of enzyme activity were observed. The mixed culture produced lower levels of enzyme activity (with the exception of Β-glucosidase) particularly during the initial states of degradation. Differences in enzyme production by A. fumigatus and P. simplicissimum were also observed. A. fumigatus produced high levels of xylanase and endoglucanase while P. simplicissimum produced high levels of exoglucanase. Similar results were observed on straw. The composition of the lignocellulosic material was measured by sequential chemical extraction of the solubles, hemicellulose, cellulose, and lignin. Changes in the composition during degradation were investigated. During the growth of all three cultures on hay, the total percentage of hemicellulose and cellulose decreased from 84% to less than 45% in 40 d. Despite significant differences in the enzyme activity, P. simplicissimum, A. fumigatus and the mixed culture were capable of degrading lignocellulosic material at the same rate. The production of a full cellulase complex appears to be more important than the production of high levels of individual enzymes.     

Path coverings of the vertices of a tree

Consider a collection of disjoint paths in graph G such that every vertex is on one of these paths. The size of the smallest such collection is denoted i(G). A procedure for forming such collections is established. Restricting attention to trees, the range of values for the sizes of the collections obtained is examined, and a constructive characterization of trees T for which one always obtains a collection of size i(T) is presented.     

Accretion centers: A generalization of branch weight centroids

An ordered n-tuple (v_i1,v_i2,…,v_in) is called a sequential labelling of graph G if {v_i1,v_i2,…,v_in} = V(G) and the subgraph induced by {v_i1,v_i2,…, v_ij} is connected for 1≤j≤n. Let σ(v;G) denote the number of sequential labellings of G with v_i1=v. Vertex v is defined to be an accretion center of G if σ is maximized at v. This is shown to generalize the concept of a branch weight centroid of a tree since a vertex in a tree is an accretion center if and only if it is a centroid vertex. It is not, however, a generalization of the concept of a median since for a general graph an accretion center is not necessarily a vertex of minimum distance. A method for computing σ(v;G) based upon edge contractions is described.     

Calculation of the magnetization and total energy of vanadium as a function of lattice parameter

Self-consistent spin-polarized APW calculations have been performed to determine the energy band structure of metallic vanadium in an assumed ferromagnetic b.c.c. structure as a function of lattice parameter. The statistical exchange (‘Xα’) and muffin-tin approximations were used. At each lattice parameter for which a calculation was performed, the Xα cohesive energy, the pressure, and the magnetization were calculated. The calculated cohesive energy and pressure agree fairly well with experiment. The calculations also correctly predict the absence of a magnetic moment for vanadium at its equilibrium lattice constant. However, a nonmagnetic-to-magnetic transition is found to occur abruptly at a lattice constant which is about a factor of 1·25 larger than the equilibrium value, and which is in good qualitative agreement with the appearance of a local magnetic moment in certain vanadium alloys.     

Counterexamples to randić's conjecture on distance degree sequences for trees

As counterexamples to a conjecture of Randi?, pairs of nonisomorphic trees with the same collections of distance degree sequences are presented.     

On graphs containing a given graph as center

We examine the problem of embedding a graph H as the center of a supergraph G, and we consider what properties one can restrict G to have. Letting A(H) denote the smallest difference ∣V(G)∣ - ∣V(H)∣ over graphs G having center isomorphic to H it is demonstrated that A(H) ≤ 4 for all H, and for 0 ≤ i ≤ 4 we characterize the class of trees T with A(T) = i. for n ≥ 2 and any graph H, we demonstrate a graph G with point and edge connectivity equal to n, with chromatic number X(G) = n + X(H), and whose center is isomorphic to H. Finally, if ∣V(H)∣ ≥ 9 and k ≥ ∣V(H)∣ + 1, then for n sufficiently large (with n even when k is odd) we can construct a k-regular graph on n vertices whose center is isomorphic to H.     

A limit on the lepton-family number violating process π → μe

A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π⁰ → μ^±e using π⁰'s produced from K_L → π⁰π⁰π⁰ decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on

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was determined to be 8.6 × 10⁻⁹.     

Metal-metal interactions in dinuclear ruthenium complexes containing bridging 4,5-di(2-pyridyl)imidazolates and related ligands

The dinuclear bis(2,2'-bipyridine)ruthenium complex of 4,5-di(2-pyridyl)imidazolate has been prepared and separated into its (meso and rac) diastereoisomers. The 2-phenyl substituted analogue forms the meso isomer selectively. All three complexes have been characterised by 1H NMR and X-ray crystallography. Electrochemical measurements and spectroelectrochemistry of the mixed-valence states reveal strong metal-metal interactions and IVCT bands that are highly dependent on the electrolyte.