Conventional Two-stage Research Articles

An efficient photochemical bleaching of kraft pulps using total halogen-free reducing reagents

Total chlorine-free bleaching of kraft pulps was conducted by a reductive photochemical process at room temperature. Reducing reagents were screened, and bleaching conditions were optimized using excimer lasers. The laser used in the best bleaching condition was then substituted by conventional light sources to make the process more easily accessible. The most favorable condition for the bleaching of kraft pulps was irradiation with a low-pressure mercury lamp in the presence of aqueous sodium borohydride solution, which gave bleaching efficiency and the properties of pulps similar to those obtained by a conventional two-stage, elemental chlorine-free process. The photochemical background of the bleaching is discussed.

Immediate Loading

I should begin by differentiating this concept from Immediate Placement (non-exact osteotomy with bone regenerative techniques) in conjunction with Immediate Loading. Immediate load as discussed in this essay refers to an interim or temporary restoration on a “just placed” implant fixture. While attending a formal oral implantology fellowship at the University of Pittsburgh in 1986, we were taught to understand and appreciate the efforts and accomplishments of those pioneers dedicated to the desire to help those patients whom conventional dental education and techniques could not satisfy. We hear how history has a way of repeating itself (that’s why it should be studied) and that few ideas are actually new. This is one of those ideas. Turning a two-stage protocol, as we understand it, into a one-stage technique is just turning the clock back from 1982 to 1972 and presenting this idea in 2002! This history, along with the evolution of implant materials and better bone physiology understanding, bring the need for, and practicality of, immediate loading to the forefront. The desire and demand for implant restorations have grown tremendously. Single-tooth restorative dentistry, often achieved via dental implants, is more predictable and successful than complex and advanced restorative dentistry requiring multiple abutments, pontics, and precision attachments. With the concept of interceptive prosthodontics, immediate load protocol is our most current challenge. This challenge must be approached with a scientific basis and understanding to be resolved. Applied research as it relates to a predictable outcome for our patients must be a science that applies to all clinicians, not a skill that can be mastered by only a few. We must separate our desire to help our patients from the actual bone physiology of healing. The big question is whether we are able to handle any prosthetic issues during healing (ie, occlusion, esthetics, function, etc.) without compromising the bone’s ability to stabilize the implant fixture as it osseointegrates. For predictable clinical dentistry we must calculate risks and minimize errors. In private practice communities, who will be responsible for the added failures? If we accept a 5 to 10% failure rate with immediate implant loading, when we are accustomed to a 1% failure rate with conventional two-stage implant protocol, then who explains and absorbs the costs of money and time? Private dental practice is not a research situation that is grant-based or state subsidized, but is patient-based relying on the judgment and expertise of the dental implant team. Who will place, reline, and adjust the interim prosthesis at the time of surgery before closure? By immediately loading the implant, are we evolving away from the team concept to a one-stop shop concept? Are we potentially disillusioning patients by presenting a possible “immediate gratification” that may prove to diminish the long-term quality of the treatment outcome? Immediate load concepts are further limited in implant overdenture prosthetics as the support bar is either prefabricated or designed by connecting the implants over the existing ridge. With a two-stage approach, the implant bar is created to develop a “new ridge” that can support the intended tooth position. With this approach, the implant bar can be fabricated in the proper buccolingual, anterioposterior, and vertical location to properly support the prosthesis. Prosthetic techniques used with immediate loading may give patients “teeth in a day,” but isn’t the profession more directed toward benefits for a lifetime? Patients are paying higher fees for less time and receiving less than desired results. The philosophy of a two-stage dental implant protocol has provided a predictable, scientifically based method for patient care and brought implant dentistry out of the “dark ages.” It has provided the opportunity to change the philosophy of restorative dentistry. It has given patients and practitioners new hope with excellent results. Studies have shown that primary bone stabilization of the implant fixture may occur 2 months after initial placement. I present that as a first step toward reaching immediate loading. We should first look at indexing of the implant at the time of first stage surgery, then place a provisional restoration at uncovery 2 months later. I believe we must be comfortable with this approach initially, doing it routinely and achieving excellent results. This technique allows everyone in the implant team to develop their skills, improve their communication, decrease risks, and evaluate their results. Currently, I feel that possible indications for using immediate dental implant loading (with associated risks) are as follows: Teeth receiving minimal load (eg, maxillary lateral incisors, teeth with no opposing occlusion, etc.). The ability to temporarily splint the provisional implant restoration to adjacent teeth or integrated implants. Dense Type II bone. I look forward to and believe that Immediate Loading will continue to evolve and mature and that scientific research will clarify its predictability in our implant treatment plans. ** John P. Davliakos, DMD

Synthesis and Properties of 1,4-Bis(4-aminophenoxy)naphthalene and Its Polyimides

A new diamine 1,4-bis(4-aminophenoxy)naphthalene (1,4-BAPON) was prepared through the nucleophilic displacement of 1,4-dihydroxynaphthalene with p-fluoronitrobenzene in the presence of K2CO3 in N,N-dimethylacetamide (DMAc), followed by catalytic reduction with hydrazine and Pd/C in ethanol. A series of novel aromatic polyimides containing 1,4-bis(aminophenoxy)naphthalene units was synthesized from 1,4-BAPON and various aromatic tetracarboxylic dianhydrides by the conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as DMAc, to give poly(amic acid)s, followed by thermal cyclodehydration to polyimides. Depending on the dianhydrides used, the poly(amic acid)s obtained had inherent viscosities of 0.81–1.33 dL g−1. All the poly(amic acid)s could be solution cast and thermally converted into transparent, flexible, and tough polyimide films. These polyimides had glass transition temperatures between 247–281°C. Thermogravimetric analyses established that these polymers were fairly stable up to 500°C, and 10% weight loss temperatures were recorded in the range of 521–581°C in nitrogen and 517–575°C in air atmosphere.

Synthesis and evaluation of novel polyimides derived from spirobichroman diether anhydride

A spirobichroman structure-containing diether anhydride (SBCDA), 6,6′-bis(3,4-dicarboxyphenoxy)-4,4,4′,4′,7,7′-hexamethyl-2,2′-spirobichroman dianhydride, was prepared by the nucleophilic nitrodisplacement of 4-nitrophthalonitrile with the phenolate ion of 6,6′-dihydroxy-4,4,4′,4′,7,7′-hexamethyl-2,2′-spirobichroman, followed by alkaline hydrolysis of the intermediate tetranitrile and dehydration of the resulting tetraacid. A series of high molecular weight poly(ether imide)s with inherent viscosities between 0.45 and 1.28 dL/g were synthesized from SBCDA and various aromatic diamines via a conventional two-stage procedure that included ring-opening polyaddition in N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by thermal cyclization to poly(ether imide)s. The intermediate poly(amic acid)s had inherent viscosities of 0.70–1.50 dL/g. Except for the poly(ether imide) obtained from p-phenylenediamine, the other poly(ether imide)s were soluble in various organic solvents and could be solution-cast into transparent, flexible, and tough films. These poly(ether imide)s had glass transition temperatures in the range 175–262°C and showed no significant decomposition below 420°C, with 10% weight loss being recorded above 446°C in nitrogen or air. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2801–2809, 1997

Synthesis and properties of polyimides derived from 3,3′,5,5′-tetramethyl-bis[4-(4-aminophenoxy)phenyl]sulfone

The novel diamine containing methyl-substituted arylene sulfone ether, 3,3′5,5′-tetramethylbis[4-(4-aminophenoxy)phenyl]sulfone (TBAPS), was used as a monomer with various aromatic tetracarboxylic dianhydrides to synthesize polyimides via a conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by cyclodehydration to polyimides. The diamine was prepared through the nucleophilic displacement of bis(4-hydroxy-3,5-dimethylphenyl)sulfone with p-chloronitrobenzene in the presence of K 2 CO 3, followed by catalytic reduction. Depending on the dianhydrides used, the poly(amic acid)s obtained had inherent viscosities of 0.80−1.72 dL g −1. All the poly(amic acid)s could be cast from DMAc solutions and thermally converted into transparent, flexible and tough polyimide films. The polyimide films had a high tensile strength range 81–118 MPa, an elongation range at break 5–9% and a tensile modulus range 1.78–2.49 GPa. The polyimide derived from 4,4′-hexafluoroisopropylidenebis-phathalic anhydride had better solubility than the other polyimides. These polyimides had glass transition temperatures between 291–339 °C and 10% mass loss temperatures were recorded in the range 550–591 °C in nitrogen and 556–588 °C in air atmosphere.

Synthesis and properties of polyimides derived from 1,4-Bis(4-Aminophenoxy)2,5-di-tert-Butylbenzene

Novel aromatic polyimides containing symmetric, bulky di-tert-butyl substituents unit were synthesized from 1,4-bis(4-aminophenoxy)2,5-di-tert-butylbenzene (BADTB) and various aromatic tetracarboxylic dianhydrides by the conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide to give poly(amic acid)s, followed by cyclodehydration to polyimides. The diamine was prepared through the nucleophilic displacement of 2,5-di-tert-butylhydroquinone with p-chloronitrobenzene in the presence of K2CO3, followed by catalytic reduction. Depending on the dianhydrides used, the poly(amic acid)s obtained had inherent viscosities of 0.83–1.88 dL g−1. Most of the polyimides formed transparent, flexible, and tough films. Tensile strength and elongation at break of the BADTB-based polyimide films ranged from 68–93 MPa and 7–11%, respectively. The polyimide derived from 4,4′-hexafluoro-isopropylidenebisphathalic anhydride had better solubility than the other polyimides. These polyimides had glass transition temperatures between 242–298°C and 10% mass loss temperatures were recorded in the range of 481–520°C in nitrogen. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1527–1534, 1997

Synthesis and Properties of Polyimides Derived from 1,4-Bis(4-aminophenoxy)-2-tert-butylbenzene

The novel diamine containing bulky tert-butyl substituent, 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene (BATB) was used as monomer with various aromatic tetracarboxylic dianhydrides to synthesize polyimides via a conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by cyclodehydration to polyimides. BATB(II) was prepared through the nucleophilic displacement of tert-butylhydroquinone with p-chloronitrobenzene in the presence of K2CO3, followed by catalytic reduction. Depending on the dianhydride used, the poly(amic acid)s obtained had inherent viscosities of 0.76–1.79 dL g−1. All poly(amic acid)s could be cast from the DMAc solutions and thermally converted to transparent, fiexible, and tough polyimide films. The polyimide films had high tensile strength of 122–208 MPa, an elongation at breaks of 3–9%, and a tensile modulus of 1.92–2.68 GPa. Polyimides from 4,4′-sulfonyldiphthalic anhydride and 4,4′-hexafluoro-isopropylidenediphathalic anhydride had better solubility than the other polyimides. These polyimides had glass transition temperatures between 240–268°C and 10% mass loss temperatures were recorded at 479–522°C in nitrogen.

Design of suspension systems for measurement of high-Q pendulums

Laser interferometer gravitational wave detectors require the use of massive ultra-high-Q test mass pendulums to minimize thermal noise. The verification of ultra-high Q-factors in pendulums is difficult due to the coupling of support structure recoil losses into the pendulum stage. We present a numerical analysis of three different pendulum suspension systems to assess their performance. We show that conventional two-stage and three-stage suspension systems cannot be expected to verify Q-factors beyond 108 due to recoil losses, but that a twin pendulum system can allow Q-factors of 1010 to be observed.

Considerations for fast settling operational amplifiers

The design considerations for fast-settling operational amplifiers (op amps) are significantly different between sampled-data switched-capacitor (SC) and conventional continuous-time applications. In SC circuits, the shape of the output voltage waveform of an op amp is of no consequence provided that the output settles to within a specified tolerance of its steady-state value prior to the next sampling instant. This feature allows for an optimum op amp frequency shaping to obtain a minimum small-signal settling time. The theory applies to any op amp that is well approximated by a two-pole model, including the conventional two-stage and single-stage folded-cascode topologies. As the commonly used equivalent-circuit Miller-effect model for frequency compensation has generally been improperly applied to two-stage transconductance amplifiers, it does not provide sufficient accuracy to achieve the optimum phase margin condition. Therefore, the use of equivalent-circuit models has been refined to provide greater accuracy and to eliminate some previous misconceptions. >