Customer Churn Prediction Based on BG / NBD Model

With the rapid development of information technology, most enterprises have built e-commerce platform, which promotes the revolution of operation mode. The focus of competition gradually becomes the customers rather than the products under the increasingly fierce market competition of the E-commerce model. Because of the non-contractual relationship between the customers and the e-commerce platform, maintaining the stable customer relationship becomes the necessary condition for the e-commerce enterprises to get profit. So predicting the customer churn accurately plays an important role in the development of e-commerce enterprises. In this paper, the BG / NBD model is used to analyze the historical transaction records of an e-commerce platform in order to analyze and predict the purchase behavior of the existing customers, and identify the pre-losing customers, which helps the enterprises to implement the more effective strategies of CRM and restore the pre-loss customers timely

2,2′-[Ethane-1,2-diylbis(sulfanedi­yl)]bis­(pyridine N-oxide)

The tile compound, C12H12N2O2S2, lies on an inversion center. The two pyridyl rings are parallel to each other. The structure is devoid of any classical hydrogen bonds due to lack of appropriate donors and acceptors for such bonds. However, non-classical hydrogen bonds of the types C—H⋯O and C—H⋯S stabilize the structure

Authigenesis, biomineralization, and carbon-sulfur cycling in the Ediacaran ocean

Fossil record of the Ediacaran Period (635-541 Ma) reveals unprecedented rise of early animal life (metazoan) in Earth history. Coupled with this evolutionary milestone, the Earth’s atmosphere and hydrosphere experienced dramatic redox fluctuations. In order to better constrain the redox architecture of the Ediacaran ocean margin, an integrated chemostratigraphic correlation of the Doushantuo Formation in basin scale was conducted (see Chapter 2). The revised redox model suggests that euxinic conditions on the platforms were mainly restricted in lagoonal settings, which helps us to better understand Ediacaran fossil distributions and fluctuated δ13C records in the Ediacaran strata in South China. One of the most distinct features of the Ediacaran chemostratigraphy is the δ13C negative excursion (i.e. Shuram Excursion, or SE) reported globally, which is the largest known C cycle anomaly in Earth history. In order to understand the biogeochemical processes that gave rise to the SE expressed in the upper Doushantuo Formation, systematic petrographic and geochemical investigations were conducted for the outer shelf sections in the Yangtze block (see Chapter 3). Methane-derived authigenic calcite cements and nodules with extreme 13C-depletion were discovered and interpreted as the first empirical evidence of authigenic mineralization associated with the SE. In light of these novel observations, it is proposed that the globally distributed SE may be formed by widespread syndeposition of authigenic carbonates in a sulfate-methane transitional zone positioned at the sediment-water interface in response to a global seawater sulfate increase. Finally, to provide environmental context for the terminal Ediacaran biomineralization of animals, we conducted a high-resolution elemental and isotopic study of the richly fossiliferous Gaojiashan Member (see Chapter 4). Coincident with the first appearance of Cloudina are significant C-S-Ca-Sr cycle anomalies. It is proposed that the onset of calcarious biomineralization of animals may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin. Enhanced concentration of Ca ion in seawater may have promoted the calcarious biomineralization of the early animals. Integrated chemo-, bio- and litho-stratigraphy of the Doushantuo and Dengying formations presented in this dissertation emphasized intimate co-evolution of Earth-life system during the Ediacaran Period

[μ2-Bis(diphenyl­phosphanyl)methane][μ3-bis­(diphenyl­phosphanyl)meth­yl]trichlorido­tetra­gold(I) tetra­hydro­furan disolvate

The title tetra­nuclear complex, [Au4(C25H21P2)Cl3(C25H22P2)]·2C4H8O, features two non-equivalent Ph2PCPPh2 fragments, one of which represents the ‘complete’ mol­ecule (with two H atoms at the central C atom); each of the two P atoms of this mol­ecule is coordinated by an Au atom [Au—P = 2.2256 (13) and 2.2710 (13) Å], and these two Au atoms form an Au—Au bond [3.2945 (3) Å], thus closing the five-membered Au2P2C ring. The first of these Au atoms has a terminal chlorido ligand [Au—Cl = 2.2806 (12) Å], whereas the second Au atom forms a covalent bond with the central C atom of the bis­(diphenyl­phosphino)methyl group [Au—C = 2.114 (5) Å]; the latter group in turn coordinates with its P atoms the gold atoms of the Cl–Au–Au–Cl group [Au—P = 2.2356 (13) and 2.2338 (13), Au—Au = 3.3177 (3), Au—Cl = 2.3091 (12) and 2.2950 (13) Å], thus closing the second Au2P2C ring. The two such rings have different chemical functions, but both exhibit envelope conformations. However, the first (with different substituents at the Au atoms) is non-symmetrical with one of the P atoms in the flap position of the envelope; the other one has a conformation with mirror symmetry, and the gold-substituted C atom is displaced by 0.740 (5) Å from the almost exactly planar (r.m.s. deviation = 0.0038 Å) Au2P2 group

Dimethyl 4,4′-(pyridine-2,6-diyl)dibenzoate

The title mol­ecule, C21H17NO4, reveals axial symmetry, with the pyridine N atom located on a crystallographic twofold axis. The mol­ecule is dish-shaped, with dihedral angles between the benzene and pyridine rings of 24.643 (1) and 24.797 (1)°, respectively. The –COO plane and the benzene ring are almost coplanar [dihedral angle = 5.286 (1)°]

Bis[μ-4-methyl-2-(2-pyridyl­methyl­sulfan­yl)pyrimidine-κN 1]bis­[(trifluoro­methanesulfonato-κO)silver(I)]

In the centrosymmetric dinuclear title complex, [Ag2(CF3SO3)2(C11H11N3S)2], the AgI atom is coordinated by two N atoms from two 4-methyl-2-(2-pyridyl­methyl­sulfan­yl)pyrimidine ligands and one O atom from a trifluoro­methane­sulfonate anion in a distorted T-type coordination geometry. The ligand adopts a bidentate bridging coordination mode through one pyridyl N atom and one pyrimidine N atom. In the crystal structure, π–π inter­actions are present between adjacent pyrimidine rings, with a centroid-to-centroid distance of 3.875 (7) Å

Diaqua­bis­(2-oxo-2H-chromene-3-carboxyl­ato)copper(II)

In the title compound, [Cu(C10H5O4)2(H2O)2], the CuII atom lies on a crystallographic inversion center and exhibits an octa­hedral coordination defined by two O atoms from water mol­ecules in the axial positions and by four O atoms from two deprotonated coumarin-3-carb­oxy­lic acid ligands in the equatorial positions. The angles around the CuII atom vary between 85.32 (6) and 94.68 (6)°. The Cu—O bond distances between the CuII atom and the O atoms vary between 1.9424 (14) and 2.3229 (15) Å. The layers inter­digitate via face-to-face aromatic inter­actions [3.6490 (8) Å] between coumarin moieties such that the inter­layer separation is 10.460 (2) Å, i.e. the length of the c axis. O—H⋯O hydrogen bonds between the H atoms of coordinated water mol­ecules and the O atoms of carboxyl­ate groups link the complex mol­ecules into layers parallel to the ab plane

Diaqua­bis­(2-oxo-2H-chromene-3-carboxyl­ato-κ2 O 2,O 3)manganese(II)

In the title compound, [Mn(C10H5O4)2(H2O)2], the MnII atom lies on a crystallographic inversion center and is six-coordinated by two O atoms from water mol­ecules in the axial positions and four O atoms from two deprotonated coumarin-3-carb­oxy­lic acid ligands in the equatorial plane. The overall coordination geometry is slightly distorted octa­hedral. The Mn—O bond distances vary between 2.0931 (12) and 2.2315 (13) Å. O—H⋯O hydrogen bonds between the H atoms of coordinated water mol­ecules and the O atoms of the carboxyl­ate groups link the complex mol­ecules into two-dimensional layers parallel to the ab plane